diff --git a/CHANGELOG.md b/CHANGELOG.md
index 4d38d8f0df..ba2a0b5c2b 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -71,6 +71,7 @@
 - Cleanup: remove tracking of uncurried state in parser/printer. https://github.com/rescript-lang/rescript-compiler/pull/6888
 - Remove `%opaque` primitive. https://github.com/rescript-lang/rescript-compiler/pull/6892
 - Reunify JsxC/JsxU -> Jsx etc. https://github.com/rescript-lang/rescript-compiler/pull/6895
+- Remove the transformation of `foo(1,2)` into `Js.Internal.opaqueFullApply(Internal.opaque(f), 1, 2)`, and change the back-end to treat all applications as uncurried. https://github.com/rescript-lang/rescript-compiler/pull/6893
 
 #### :nail_care: Polish
 
diff --git a/jscomp/core/lam_compile.ml b/jscomp/core/lam_compile.ml
index 8161894bf9..4065d9c27f 100644
--- a/jscomp/core/lam_compile.ml
+++ b/jscomp/core/lam_compile.ml
@@ -1531,15 +1531,10 @@ and compile_prim (prim_info : Lam.prim_info)
          check the arity of fn before wrapping it
          we need mark something that such eta-conversion can not be simplified in some cases
       *)
-  | {
-   primitive = Pjs_unsafe_downgrade { name = property; setter };
-   args = [ obj ];
-  } -> (
-      (*
-       either a getter {[ x #. height ]} or {[ x ## method_call ]}
-    *)
-      assert (not setter);
-
+  | { primitive = Pjs_unsafe_downgrade { name = property; setter=false };
+      args = [ obj ];
+    } -> (
+      (* getter {[ x #. height ]} *)
       match
         compile_lambda { lambda_cxt with continuation = NeedValue Not_tail } obj
       with
@@ -1555,18 +1550,10 @@ and compile_prim (prim_info : Lam.prim_info)
           in
           Js_output.output_of_block_and_expression lambda_cxt.continuation
             blocks ret)
-  | {
-   primitive = Pfull_apply;
-   args =
-     [
-       Lprim
-         {
-           primitive = Pjs_unsafe_downgrade { name = property; setter = true };
-           args = [ obj ];
-         };
-       setter_val;
-     ];
-  } -> (
+  | { primitive = Pjs_unsafe_downgrade { name = property; setter = true };
+      args = [ obj; setter_val ];
+    }  -> (
+      (* setter {[ x ## method_call ]} *)
       let need_value_no_return_cxt =
         { lambda_cxt with continuation = NeedValue Not_tail }
       in
@@ -1589,10 +1576,7 @@ and compile_prim (prim_info : Lam.prim_info)
           | Some (obj_code, obj) ->
               cont obj_block arg_block (Some obj_code)
                 (E.seq (E.assign (E.dot (E.var obj) property) value) E.unit)))
-  | {
-   primitive = Pfull_apply;
-   args = Lprim { primitive = Pjs_unsafe_downgrade { setter = true } } :: _;
-  } ->
+  | { primitive = Pjs_unsafe_downgrade _; args } ->
       assert false
   | { primitive = Pfull_apply | Pvoid_run; args; loc } -> (
       (* 1. uncurried call should not do eta-conversion
diff --git a/jscomp/core/lam_convert.ml b/jscomp/core/lam_convert.ml
index 3131bedcd0..442dfe4ab1 100644
--- a/jscomp/core/lam_convert.ml
+++ b/jscomp/core/lam_convert.ml
@@ -161,7 +161,7 @@ let unit = Lam.unit
 let lam_prim ~primitive:(p : Lambda.primitive) ~args loc : Lam.t =
   match p with
   | Pidentity -> Ext_list.singleton_exn args
-  | Puncurried_apply | Pccall _ -> assert false
+  | Pccall _ -> assert false
   | Prevapply -> assert false
   | Pdirapply -> assert false
   | Ploc _ -> assert false (* already compiled away here*)
@@ -527,11 +527,29 @@ let convert (exports : Set_ident.t) (lam : Lambda.lambda) :
     match lam with
     | Lvar x -> Lam.var (Hash_ident.find_default alias_tbl x x)
     | Lconst x -> Lam.const (Lam_constant_convert.convert_constant x)
+    | Lapply { ap_func = ((Lsend (name, obj, loc))); ap_args } when Ext_string.ends_with name Literals.setter_suffix ->
+      let obj = convert_aux obj in
+      let args = obj :: (Ext_list.map ap_args convert_aux) in
+      let property =
+          (String.sub name 0
+              (String.length name - Literals.setter_suffix_len))
+      in
+      prim
+        ~primitive:(Pjs_unsafe_downgrade { name = property; setter=true })
+        ~args loc
+    | Lsend (name, obj, loc) ->
+        let obj = convert_aux obj in
+        let args = [ obj ] in
+        let setter = Ext_string.ends_with name Literals.setter_suffix in
+        let _ = assert (not setter) in
+        prim
+          ~primitive:(Pjs_unsafe_downgrade { name; setter })
+          ~args loc
     | Lapply { ap_func = fn; ap_args = args; ap_loc = loc; ap_inlined } ->
         (* we need do this eargly in case [aux fn] add some wrapper *)
         Lam.apply (convert_aux fn)
           (Ext_list.map args convert_aux)
-          { ap_loc = loc; ap_inlined; ap_status = App_na }
+          { ap_loc = loc; ap_inlined; ap_status = App_uncurry }
     | Lfunction { params; body; attr } ->
         let new_map, body =
           rename_optional_parameters Map_ident.empty params body
@@ -566,16 +584,6 @@ let convert (exports : Set_ident.t) (lam : Lambda.lambda) :
           may_depend may_depends (Lam_module_ident.of_ml ~dynamic_import id);
           assert (args = []);
           Lam.global_module ~dynamic_import id)
-    | Lprim
-        ( Puncurried_apply,
-          [ Lapply { ap_func; ap_args } ],
-          loc ) ->
-        let ap_func = convert_aux ap_func in
-        let ap_args = Ext_list.map ap_args convert_aux in
-        prim ~primitive:Pfull_apply ~args:(ap_func :: ap_args) loc
-        (* There may be some optimization opportunities here
-           for cases like `(fun [@bs] a b -> a + b ) 1 2 [@bs]` *)
-    | Lprim (Puncurried_apply, _, _) -> assert false
     | Lprim (primitive, args, loc) ->
         let args = Ext_list.map args (convert_aux ~dynamic_import) in
         lam_prim ~primitive ~args loc
@@ -611,19 +619,6 @@ let convert (exports : Set_ident.t) (lam : Lambda.lambda) :
     | Lfor (id, from_, to_, dir, loop) ->
         Lam.for_ id (convert_aux from_) (convert_aux to_) dir (convert_aux loop)
     | Lassign (id, body) -> Lam.assign id (convert_aux body)
-    | Lsend (name, obj, loc) ->
-        let obj = convert_aux obj in
-        let args = [ obj ] in
-        let setter = Ext_string.ends_with name Literals.setter_suffix in
-        let property =
-          if setter then
-            (String.sub name 0
-                (String.length name - Literals.setter_suffix_len))
-          else name
-        in
-        prim
-          ~primitive:(Pjs_unsafe_downgrade { name = property; setter })
-          ~args loc
   and convert_let (kind : Lam_compat.let_kind) id (e : Lambda.lambda) body :
       Lam.t =
     match (kind, e) with
diff --git a/jscomp/frontend/ast_literal.ml b/jscomp/frontend/ast_literal.ml
index 5ee13ec6aa..af71328945 100644
--- a/jscomp/frontend/ast_literal.ml
+++ b/jscomp/frontend/ast_literal.ml
@@ -49,10 +49,6 @@ module Lid = struct
 
   let type_bool : t = Lident "bool" (* use *predef* *)
 
-  (* TODO should be renamed in to {!Js.fn} *)
-  (* TODO should be moved into {!Js.t} Later *)
-  let js_internal : t = Ldot (Lident "Js", "Internal")
-
   let js_oo : t = Lident "Js_OO"
 
   let js_meth_callback : t = Ldot (js_oo, "Callback")
diff --git a/jscomp/frontend/ast_literal.mli b/jscomp/frontend/ast_literal.mli
index 9e8d1cbdee..059b178dac 100644
--- a/jscomp/frontend/ast_literal.mli
+++ b/jscomp/frontend/ast_literal.mli
@@ -56,8 +56,6 @@ module Lid : sig
   val js_null_undefined : t
 
   val js_re_id : t
-
-  val js_internal : t
 end
 
 type expression_lit = Parsetree.expression lit
diff --git a/jscomp/gentype_tests/typescript-react-example/src/ImmutableArray.res.js b/jscomp/gentype_tests/typescript-react-example/src/ImmutableArray.res.js
index 630eccaa40..8f0f909427 100644
--- a/jscomp/gentype_tests/typescript-react-example/src/ImmutableArray.res.js
+++ b/jscomp/gentype_tests/typescript-react-example/src/ImmutableArray.res.js
@@ -18,13 +18,9 @@ function size(a) {
   return a.length;
 }
 
-function get(a, x) {
-  return Belt_Array.get(a, x);
-}
+let get = Belt_Array.get;
 
-function getExn(a, x) {
-  return Belt_Array.getExn(a, x);
-}
+let getExn = Belt_Array.getExn;
 
 function getUnsafe(a, x) {
   return a[x];
@@ -34,13 +30,9 @@ function getUndefined(a, x) {
   return a[x];
 }
 
-function shuffle(x) {
-  return Belt_Array.shuffle(x);
-}
+let shuffle = Belt_Array.shuffle;
 
-function reverse(x) {
-  return Belt_Array.reverse(x);
-}
+let reverse = Belt_Array.reverse;
 
 function makeUninitialized(x) {
   return new Array(x);
@@ -50,21 +42,13 @@ function makeUninitializedUnsafe(x) {
   return new Array(x);
 }
 
-function make(x, y) {
-  return Belt_Array.make(x, y);
-}
+let make = Belt_Array.make;
 
-function range(x, y) {
-  return Belt_Array.range(x, y);
-}
+let range = Belt_Array.range;
 
-function rangeBy(x, y, step) {
-  return Belt_Array.rangeBy(x, y, step);
-}
+let rangeBy = Belt_Array.rangeBy;
 
-function makeByU(c, f) {
-  return Belt_Array.makeByU(c, f);
-}
+let makeByU = Belt_Array.makeByU;
 
 function makeBy(c, f) {
   return Belt_Array.makeBy(c, (function (x) {
@@ -72,9 +56,7 @@ function makeBy(c, f) {
   }));
 }
 
-function makeByAndShuffleU(c, f) {
-  return Belt_Array.makeByAndShuffleU(c, f);
-}
+let makeByAndShuffleU = Belt_Array.makeByAndShuffleU;
 
 function makeByAndShuffle(c, f) {
   return Belt_Array.makeByAndShuffle(c, (function (x) {
@@ -82,13 +64,9 @@ function makeByAndShuffle(c, f) {
   }));
 }
 
-function zip(a1, a2) {
-  return Belt_Array.zip(a1, a2);
-}
+let zip = Belt_Array.zip;
 
-function zipByU(a1, a2, f) {
-  return Belt_Array.zipByU(a1, a2, f);
-}
+let zipByU = Belt_Array.zipByU;
 
 function zipBy(a1, a2, f) {
   return Belt_Array.zipBy(a1, a2, (function (x, y) {
@@ -96,33 +74,21 @@ function zipBy(a1, a2, f) {
   }));
 }
 
-function unzip(a) {
-  return Belt_Array.unzip(a);
-}
+let unzip = Belt_Array.unzip;
 
-function concat(a1, a2) {
-  return Belt_Array.concat(a1, a2);
-}
+let concat = Belt_Array.concat;
 
-function concatMany(a) {
-  return Belt_Array.concatMany(a);
-}
+let concatMany = Belt_Array.concatMany;
 
-function slice(a, offset, len) {
-  return Belt_Array.slice(a, offset, len);
-}
+let slice = Belt_Array.slice;
 
-function sliceToEnd(a, b) {
-  return Belt_Array.sliceToEnd(a, b);
-}
+let sliceToEnd = Belt_Array.sliceToEnd;
 
 function copy(a) {
   return a.slice(0);
 }
 
-function forEachU(a, f) {
-  Belt_Array.forEachU(a, f);
-}
+let forEachU = Belt_Array.forEachU;
 
 function forEach(a, f) {
   Belt_Array.forEach(a, (function (x) {
@@ -130,9 +96,7 @@ function forEach(a, f) {
   }));
 }
 
-function mapU(a, f) {
-  return Belt_Array.mapU(a, f);
-}
+let mapU = Belt_Array.mapU;
 
 function map(a, f) {
   return Belt_Array.map(a, (function (x) {
@@ -140,9 +104,7 @@ function map(a, f) {
   }));
 }
 
-function keepWithIndexU(a, f) {
-  return Belt_Array.keepWithIndexU(a, f);
-}
+let keepWithIndexU = Belt_Array.keepWithIndexU;
 
 function keepWithIndex(a, f) {
   return Belt_Array.keepWithIndex(a, (function (x, y) {
@@ -150,9 +112,7 @@ function keepWithIndex(a, f) {
   }));
 }
 
-function keepMapU(a, f) {
-  return Belt_Array.keepMapU(a, f);
-}
+let keepMapU = Belt_Array.keepMapU;
 
 function keepMap(a, f) {
   return Belt_Array.keepMap(a, (function (x) {
@@ -160,9 +120,7 @@ function keepMap(a, f) {
   }));
 }
 
-function forEachWithIndexU(a, f) {
-  Belt_Array.forEachWithIndexU(a, f);
-}
+let forEachWithIndexU = Belt_Array.forEachWithIndexU;
 
 function forEachWithIndex(a, f) {
   Belt_Array.forEachWithIndex(a, (function (x, y) {
@@ -170,9 +128,7 @@ function forEachWithIndex(a, f) {
   }));
 }
 
-function mapWithIndexU(a, f) {
-  return Belt_Array.mapWithIndexU(a, f);
-}
+let mapWithIndexU = Belt_Array.mapWithIndexU;
 
 function mapWithIndex(a, f) {
   return Belt_Array.mapWithIndex(a, (function (x, y) {
@@ -180,9 +136,7 @@ function mapWithIndex(a, f) {
   }));
 }
 
-function partitionU(a, f) {
-  return Belt_Array.partitionU(a, f);
-}
+let partitionU = Belt_Array.partitionU;
 
 function partition(a, f) {
   return Belt_Array.partition(a, (function (x) {
@@ -190,9 +144,7 @@ function partition(a, f) {
   }));
 }
 
-function reduceU(a, b, f) {
-  return Belt_Array.reduceU(a, b, f);
-}
+let reduceU = Belt_Array.reduceU;
 
 function reduce(a, b, f) {
   return Belt_Array.reduce(a, b, (function (x, y) {
@@ -200,9 +152,7 @@ function reduce(a, b, f) {
   }));
 }
 
-function reduceReverseU(a, b, f) {
-  return Belt_Array.reduceReverseU(a, b, f);
-}
+let reduceReverseU = Belt_Array.reduceReverseU;
 
 function reduceReverse(a, b, f) {
   return Belt_Array.reduceReverse(a, b, (function (x, y) {
@@ -210,9 +160,7 @@ function reduceReverse(a, b, f) {
   }));
 }
 
-function reduceReverse2U(a1, a2, c, f) {
-  return Belt_Array.reduceReverse2U(a1, a2, c, f);
-}
+let reduceReverse2U = Belt_Array.reduceReverse2U;
 
 function reduceReverse2(a1, a2, c, f) {
   return Belt_Array.reduceReverse2(a1, a2, c, (function (x, y, z) {
@@ -220,9 +168,7 @@ function reduceReverse2(a1, a2, c, f) {
   }));
 }
 
-function someU(a, f) {
-  return Belt_Array.someU(a, f);
-}
+let someU = Belt_Array.someU;
 
 function some(a, f) {
   return Belt_Array.some(a, (function (x) {
@@ -230,9 +176,7 @@ function some(a, f) {
   }));
 }
 
-function everyU(a, f) {
-  return Belt_Array.everyU(a, f);
-}
+let everyU = Belt_Array.everyU;
 
 function every(a, f) {
   return Belt_Array.every(a, (function (x) {
@@ -240,9 +184,7 @@ function every(a, f) {
   }));
 }
 
-function every2U(a1, a2, f) {
-  return Belt_Array.every2U(a1, a2, f);
-}
+let every2U = Belt_Array.every2U;
 
 function every2(a1, a2, f) {
   return Belt_Array.every2(a1, a2, (function (x, y) {
@@ -250,9 +192,7 @@ function every2(a1, a2, f) {
   }));
 }
 
-function some2U(a1, a2, f) {
-  return Belt_Array.some2U(a1, a2, f);
-}
+let some2U = Belt_Array.some2U;
 
 function some2(a1, a2, f) {
   return Belt_Array.some2(a1, a2, (function (x, y) {
@@ -260,9 +200,7 @@ function some2(a1, a2, f) {
   }));
 }
 
-function cmpU(a1, a2, f) {
-  return Belt_Array.cmpU(a1, a2, f);
-}
+let cmpU = Belt_Array.cmpU;
 
 function cmp(a1, a2, f) {
   return Belt_Array.cmp(a1, a2, (function (x, y) {
@@ -270,9 +208,7 @@ function cmp(a1, a2, f) {
   }));
 }
 
-function eqU(a1, a2, f) {
-  return Belt_Array.eqU(a1, a2, f);
-}
+let eqU = Belt_Array.eqU;
 
 function eq(a1, a2, f) {
   return Belt_Array.eq(a1, a2, (function (x, y) {
diff --git a/jscomp/gentype_tests/typescript-react-example/src/Records.res.js b/jscomp/gentype_tests/typescript-react-example/src/Records.res.js
index 04f88e58dd..36bff49322 100644
--- a/jscomp/gentype_tests/typescript-react-example/src/Records.res.js
+++ b/jscomp/gentype_tests/typescript-react-example/src/Records.res.js
@@ -19,12 +19,10 @@ function coord2d(x, y) {
   };
 }
 
-function getOpt(opt, $$default, foo) {
-  return Belt_Option.mapWithDefault(opt, $$default, foo);
-}
+let getOpt = Belt_Option.mapWithDefault;
 
 function findAddress(business) {
-  return getOpt(business.address, /* [] */0, (function (a) {
+  return Belt_Option.mapWithDefault(business.address, /* [] */0, (function (a) {
     return {
       hd: a,
       tl: /* [] */0
@@ -34,13 +32,13 @@ function findAddress(business) {
 
 function findAllAddresses(businesses) {
   return Belt_List.toArray(Belt_List.flatten(Belt_List.fromArray(Belt_Array.map(businesses, (function (business) {
-    return Belt_List.concat(getOpt(business.address, /* [] */0, (function (a) {
+    return Belt_List.concat(Belt_Option.mapWithDefault(business.address, /* [] */0, (function (a) {
       return {
         hd: a,
         tl: /* [] */0
       };
-    })), getOpt(business.owner, /* [] */0, (function (p) {
-      return getOpt(p.address, /* [] */0, (function (a) {
+    })), Belt_Option.mapWithDefault(business.owner, /* [] */0, (function (p) {
+      return Belt_Option.mapWithDefault(p.address, /* [] */0, (function (a) {
         return {
           hd: a,
           tl: /* [] */0
@@ -77,7 +75,7 @@ function getPayloadRecordPlusOne(param) {
 }
 
 function findAddress2(business) {
-  return getOpt(Caml_option.nullable_to_opt(business.address2), /* [] */0, (function (a) {
+  return Belt_Option.mapWithDefault(Caml_option.nullable_to_opt(business.address2), /* [] */0, (function (a) {
     return {
       hd: a,
       tl: /* [] */0
diff --git a/jscomp/ml/lambda.ml b/jscomp/ml/lambda.ml
index 64dec28df1..8b7489402f 100644
--- a/jscomp/ml/lambda.ml
+++ b/jscomp/ml/lambda.ml
@@ -266,7 +266,6 @@ type primitive =
   | Pasrbint of boxed_integer
   | Pbintcomp of boxed_integer * comparison
   | Pctconst of compile_time_constant
-  | Puncurried_apply
   | Pcreate_extension of string
 and comparison =
     Ceq | Cneq | Clt | Cgt | Cle | Cge
diff --git a/jscomp/ml/lambda.mli b/jscomp/ml/lambda.mli
index 37452ed423..87125870c5 100644
--- a/jscomp/ml/lambda.mli
+++ b/jscomp/ml/lambda.mli
@@ -233,7 +233,6 @@ type primitive =
   | Pasrbint of boxed_integer
   | Pbintcomp of boxed_integer * comparison
   | Pctconst of compile_time_constant
-  | Puncurried_apply
   | Pcreate_extension of string
 and comparison =
     Ceq | Cneq | Clt | Cgt | Cle | Cge
diff --git a/jscomp/ml/printlambda.ml b/jscomp/ml/printlambda.ml
index dfb7203b30..4dc4e7705e 100644
--- a/jscomp/ml/printlambda.ml
+++ b/jscomp/ml/printlambda.ml
@@ -121,7 +121,6 @@ let print_taginfo ppf = function
     -> fprintf ppf "[%s]" (String.concat ";" (Array.to_list ss) )
 
 let primitive ppf = function
-  | Puncurried_apply -> fprintf ppf "@app"
   | Pidentity -> fprintf ppf "id"
   | Pbytes_to_string -> fprintf ppf "bytes_to_string"
   | Pignore -> fprintf ppf "ignore"
@@ -253,7 +252,6 @@ let primitive ppf = function
   | Pbintcomp(bi, Cge) -> print_boxed_integer ">=" ppf bi
   | Pcreate_extension s -> fprintf ppf "extension[%s]" s   
 let name_of_primitive = function
-  | Puncurried_apply -> "Puncurried_apply"
   | Pidentity -> "Pidentity"
   | Pbytes_to_string -> "Pbytes_to_string"
   | Pignore -> "Pignore"
diff --git a/jscomp/ml/translcore.ml b/jscomp/ml/translcore.ml
index 6723662971..c0f72ed7f3 100644
--- a/jscomp/ml/translcore.ml
+++ b/jscomp/ml/translcore.ml
@@ -422,7 +422,6 @@ let primitives_table =
       ("%int64_to_int32", Pcvtbint (Pint64, Pint32));
       ("%int64_of_bigint", Pcvtbint (Pbigint, Pint64));
       ("%int64_to_bigint", Pcvtbint (Pint64, Pbigint));
-      ("%uncurried_apply", Puncurried_apply);
     ]
 
 let find_primitive prim_name = Hashtbl.find primitives_table prim_name
@@ -1037,14 +1036,8 @@ and transl_cases_try cases =
   List.map transl_case_try cases
 
 and transl_apply ?(inlined = Default_inline) ?(uncurried_partial_application=None) lam sargs loc =
-  let lapply funct args =
-    match funct with
-    (* Attention: This may not be what we need to change the application arity*)
-    | Lapply ap -> Lapply { ap with ap_args = ap.ap_args @ args; ap_loc = loc }
-    | lexp ->
-        Lapply
-          { ap_loc = loc; ap_func = lexp; ap_args = args; ap_inlined = inlined }
-  in
+  let lapply ap_func ap_args =
+    Lapply { ap_loc = loc; ap_func; ap_args; ap_inlined = inlined } in
   let rec build_apply lam args = function
     | (None, optional) :: l ->
         let defs = ref [] in
@@ -1101,11 +1094,10 @@ and transl_apply ?(inlined = Default_inline) ?(uncurried_partial_application=Non
     let extra_args = Ext_list.map extra_ids (fun id -> Lvar id) in
     let ap_args = args @ extra_args in
     let l0 = Lapply { ap_func = lam; ap_args; ap_inlined = inlined; ap_loc = loc } in
-    let l1 = Lprim (Puncurried_apply, [l0], loc) in
     Lfunction
       {
         params = List.rev_append !none_ids extra_ids ;
-        body = l1;
+        body = l0;
         attr = default_function_attribute;
         loc;
       }
diff --git a/jscomp/ml/typecore.ml b/jscomp/ml/typecore.ml
index c6f20c1706..7a76507dc4 100644
--- a/jscomp/ml/typecore.ml
+++ b/jscomp/ml/typecore.ml
@@ -2153,18 +2153,6 @@ and type_expect_ ?type_clash_context ?in_function ?(recarg=Rejected) env sexp ty
       end_def ();
       unify_var env (newvar()) funct.exp_type;
 
-      let mk_exp ?(loc=Location.none) exp_desc exp_type =
-        { exp_desc;
-          exp_loc = loc; exp_extra = [];
-          exp_type;
-          exp_attributes = [];
-          exp_env = env } in
-      let apply_internal name e =
-        let lid:Longident.t = Ldot (Ldot (Lident "Js", "Internal"), name) in
-        let (path, desc) = Env.lookup_value lid env in
-        let id = mk_exp (Texp_ident(path, {txt=lid; loc=Location.none}, desc)) desc.val_type in
-        mk_exp ~loc:e.exp_loc (Texp_apply(id, [(Nolabel, Some e)])) e.exp_type in
-        
       let mk_apply funct args =
         rue {
           exp_desc = Texp_apply(funct, args);
@@ -2178,7 +2166,7 @@ and type_expect_ ?type_clash_context ?in_function ?(recarg=Rejected) env sexp ty
         | _ -> false in
 
       if fully_applied && not is_primitive then
-        rue (apply_internal "opaqueFullApply" (mk_apply funct args))
+        rue (mk_apply funct args)
       else
         rue (mk_apply funct args)
   | Pexp_match(sarg, caselist) ->
diff --git a/jscomp/others/js.res b/jscomp/others/js.res
index 862e8a8f52..10ce264026 100644
--- a/jscomp/others/js.res
+++ b/jscomp/others/js.res
@@ -77,13 +77,6 @@ Prefer `Js.Array2` over `Js.Array`, `Js.String2` over `Js.String`, etc. The latt
 /** JS object type */
 type t<'a> = {..} as 'a
 
-module Internal = {
-  external opaqueFullApply: 'a => 'a = "%uncurried_apply"
-
-  /* Use opaque instead of [._n] to prevent some optimizations happening */
-  external run: ((. unit) => 'a) => 'a = "#run"
-}
-
 /**
   Nullable value of this type can be either null or 'a. This type is equivalent to Js.Null.t.
 */
diff --git a/jscomp/runtime/js.res b/jscomp/runtime/js.res
index 8356872162..420be9c836 100644
--- a/jscomp/runtime/js.res
+++ b/jscomp/runtime/js.res
@@ -77,13 +77,6 @@ Prefer `Js.Array2` over `Js.Array`, `Js.String2` over `Js.String`, etc. The latt
 /** JS object type */
 type t<'a> = {..} as 'a
 
-module Internal = {
-  external opaqueFullApply: 'a => 'a = "%uncurried_apply"
-
-  /* Use opaque instead of [._n] to prevent some optimizations happening */
-  external run: ((. unit) => 'a) => 'a = "#run"
-}
-
 /**
   Nullable value of this type can be either null or 'a. This type is equivalent to Js.Null.t.
 */
diff --git a/jscomp/test/UncurriedAlways.js b/jscomp/test/UncurriedAlways.js
index 6180b31cac..4b284ff2ca 100644
--- a/jscomp/test/UncurriedAlways.js
+++ b/jscomp/test/UncurriedAlways.js
@@ -72,7 +72,11 @@ function ptl$1(none, extra) {
   ];
 }
 
-let a1 = ptl$1("x", "z");
+let a1 = [
+  "x",
+  "y",
+  "z"
+];
 
 console.log("a1:", a1);
 
@@ -158,21 +162,17 @@ function fn(cb) {
   return cb();
 }
 
-((function (s) {
-    console.log({
-      NAME: "foo",
-      VAL: s
-    });
-  })());
+console.log({
+  NAME: "foo",
+  VAL: undefined
+});
 
 function fn1(a, b, param) {
   return a() + b | 0;
 }
 
 function a$1(__x) {
-  return fn1((function () {
-    return 1;
-  }), 2, __x);
+  return 3;
 }
 
 function f3(x, y, z) {
@@ -224,12 +224,10 @@ function f(a, b, c) {
 
 function f2(a, b, c, d, e) {
   let __tuple_internal_obj = a(b);
-  let param = [
-    c(__tuple_internal_obj, d),
-    d(__tuple_internal_obj, 1, 2),
-    e(__tuple_internal_obj)
-  ];
-  return (param[0] + param[1] | 0) + param[2] | 0;
+  let param_0 = c(__tuple_internal_obj, d);
+  let param_1 = d(__tuple_internal_obj, 1, 2);
+  let param_2 = e(__tuple_internal_obj);
+  return (param_0 + param_1 | 0) + param_2 | 0;
 }
 
 function f3$1(foo, x) {
diff --git a/jscomp/test/a_filename_test.js b/jscomp/test/a_filename_test.js
index 309864fbda..5fe5fd915f 100644
--- a/jscomp/test/a_filename_test.js
+++ b/jscomp/test/a_filename_test.js
@@ -44,49 +44,49 @@ if (process.platform !== "win32") {
     "/a/tmp.txt",
     "/a/tmp.txt/subdir/file.txt"
   ]);
-  eq("File \"a_filename_test.res\", line 28, characters 5-12", test({
+  eq("File \"a_filename_test.res\", line 28, characters 5-12", Ext_filename_test.node_relative_path(true, {
     NAME: "File",
     VAL: "./a/b.c"
   }, {
     NAME: "File",
     VAL: "./a/u/g.c"
   }), "./u/g.c");
-  eq("File \"a_filename_test.res\", line 31, characters 4-11", test({
+  eq("File \"a_filename_test.res\", line 31, characters 4-11", Ext_filename_test.node_relative_path(true, {
     NAME: "File",
     VAL: "./a/b.c"
   }, {
     NAME: "File",
     VAL: "xxxghsoghos/ghsoghso/node_modules/buckle-stdlib/list.js"
   }), "buckle-stdlib/list.js");
-  eq("File \"a_filename_test.res\", line 37, characters 4-11", test({
+  eq("File \"a_filename_test.res\", line 37, characters 4-11", Ext_filename_test.node_relative_path(true, {
     NAME: "File",
     VAL: "./a/b.c"
   }, {
     NAME: "File",
     VAL: "xxxghsoghos/ghsoghso/node_modules//buckle-stdlib/list.js"
   }), "buckle-stdlib/list.js");
-  eq("File \"a_filename_test.res\", line 43, characters 4-11", test({
+  eq("File \"a_filename_test.res\", line 43, characters 4-11", Ext_filename_test.node_relative_path(true, {
     NAME: "File",
     VAL: "./a/b.c"
   }, {
     NAME: "File",
     VAL: "xxxghsoghos/ghsoghso/node_modules/./buckle-stdlib/list.js"
   }), "buckle-stdlib/list.js");
-  eq("File \"a_filename_test.res\", line 48, characters 5-12", test({
+  eq("File \"a_filename_test.res\", line 48, characters 5-12", Ext_filename_test.node_relative_path(true, {
     NAME: "File",
     VAL: "./a/c.js"
   }, {
     NAME: "File",
     VAL: "./a/b"
   }), "./b");
-  eq("File \"a_filename_test.res\", line 49, characters 5-12", test({
+  eq("File \"a_filename_test.res\", line 49, characters 5-12", Ext_filename_test.node_relative_path(true, {
     NAME: "File",
     VAL: "./a/c"
   }, {
     NAME: "File",
     VAL: "./a/b.js"
   }), "./b.js");
-  eq("File \"a_filename_test.res\", line 50, characters 5-12", test({
+  eq("File \"a_filename_test.res\", line 50, characters 5-12", Ext_filename_test.node_relative_path(true, {
     NAME: "Dir",
     VAL: "./a/"
   }, {
diff --git a/jscomp/test/a_recursive_type.js b/jscomp/test/a_recursive_type.js
index e46f155b06..7727b37026 100644
--- a/jscomp/test/a_recursive_type.js
+++ b/jscomp/test/a_recursive_type.js
@@ -11,9 +11,7 @@ let loop = g({
   _0: g
 });
 
-let non_terminate = (function (x) {
-  return x._0(x);
-})({
+let non_terminate = g({
   TAG: "A",
   _0: g
 });
diff --git a/jscomp/test/a_scope_bug.js b/jscomp/test/a_scope_bug.js
index 353958d34b..f80dcfef42 100644
--- a/jscomp/test/a_scope_bug.js
+++ b/jscomp/test/a_scope_bug.js
@@ -13,9 +13,7 @@ function odd(_z) {
   };
 }
 
-function even(y) {
-  return odd(y);
-}
+let even = odd;
 
 exports.odd = odd;
 exports.even = even;
diff --git a/jscomp/test/ari_regress_test.js b/jscomp/test/ari_regress_test.js
index 55e9383ea1..da79d0742c 100644
--- a/jscomp/test/ari_regress_test.js
+++ b/jscomp/test/ari_regress_test.js
@@ -3,9 +3,7 @@
 
 let Mt = require("./mt.js");
 
-let g = (function (extra) {
-  return 3 + extra | 0;
-})(4);
+let g = 7;
 
 let h = {
   contents: 0
@@ -21,9 +19,7 @@ function g1(x, y) {
 
 let u = 8;
 
-let x = (function (z) {
-  return u + z | 0;
-})(6);
+let x = u + 6 | 0;
 
 function v(__x) {
   return g1(3, 4)(6, __x);
@@ -85,4 +81,4 @@ let suites = {
 
 Mt.from_pair_suites("Ari_regress_test", suites);
 
-/* g Not a pure module */
+/*  Not a pure module */
diff --git a/jscomp/test/arity_deopt.js b/jscomp/test/arity_deopt.js
index 9424711c78..72352a0e4b 100644
--- a/jscomp/test/arity_deopt.js
+++ b/jscomp/test/arity_deopt.js
@@ -52,17 +52,11 @@ function f3(x) {
 
 eq("File \"arity_deopt.res\", line 47, characters 11-18", 6, 6);
 
-eq("File \"arity_deopt.res\", line 48, characters 11-18", 6, (function (y, z) {
-  return (1 + y | 0) + z | 0;
-})(2, 3));
+eq("File \"arity_deopt.res\", line 48, characters 11-18", 6, 6);
 
-eq("File \"arity_deopt.res\", line 49, characters 11-18", 6, (function (z) {
-  return 3 + z | 0;
-})(3));
+eq("File \"arity_deopt.res\", line 49, characters 11-18", 6, 6);
 
-eq("File \"arity_deopt.res\", line 50, characters 11-18", 6, (function (y, z) {
-  return (1 + y | 0) + z | 0;
-})(2, 3));
+eq("File \"arity_deopt.res\", line 50, characters 11-18", 6, 6);
 
 Mt.from_pair_suites("Arity_deopt", suites.contents);
 
diff --git a/jscomp/test/async_inline.js b/jscomp/test/async_inline.js
index 423dc97bb3..e08f9e8df5 100644
--- a/jscomp/test/async_inline.js
+++ b/jscomp/test/async_inline.js
@@ -27,9 +27,7 @@ async function doSomethingAsync(someAsyncFunction) {
   return await someAsyncFunction();
 }
 
-function broken(someAsyncFunction) {
-  return doSomethingAsync(someAsyncFunction);
-}
+let broken = doSomethingAsync;
 
 let M = {
   broken: broken
@@ -39,9 +37,7 @@ async function broken$1(someAsyncFunction) {
   return await someAsyncFunction();
 }
 
-function broken$2(someAsyncFunction) {
-  return broken$1(someAsyncFunction);
-}
+let broken$2 = broken$1;
 
 function curriedId(x) {
   return x;
diff --git a/jscomp/test/bdd.js b/jscomp/test/bdd.js
index 71c28192b9..db7281675d 100644
--- a/jscomp/test/bdd.js
+++ b/jscomp/test/bdd.js
@@ -338,16 +338,16 @@ function xor(n1, n2) {
 function hwb(n) {
   let h = function (i, j) {
     if (i === j) {
-      return mkVar(i);
+      return mkNode("Zero", i, "One");
     } else {
-      return xor(and2(not(mkVar(j)), h(i, j - 1 | 0)), and2(mkVar(j), g(i, j - 1 | 0)));
+      return xor(and2(not(mkNode("Zero", j, "One")), h(i, j - 1 | 0)), and2(mkNode("Zero", j, "One"), g(i, j - 1 | 0)));
     }
   };
   let g = function (i, j) {
     if (i === j) {
-      return mkVar(i);
+      return mkNode("Zero", i, "One");
     } else {
-      return xor(and2(not(mkVar(i)), h(i + 1 | 0, j)), and2(mkVar(i), g(i + 1 | 0, j)));
+      return xor(and2(not(mkNode("Zero", i, "One")), h(i + 1 | 0, j)), and2(mkNode("Zero", i, "One"), g(i + 1 | 0, j)));
     }
   };
   return h(0, n - 1 | 0);
diff --git a/jscomp/test/bs_array_test.js b/jscomp/test/bs_array_test.js
index 9190d85d7f..c2abc8919b 100644
--- a/jscomp/test/bs_array_test.js
+++ b/jscomp/test/bs_array_test.js
@@ -194,11 +194,7 @@ let u = Belt_Array.shuffle(v$5);
 
 neq("File \"bs_array_test.res\", line 85, characters 6-13", u, v$5);
 
-function sum(x) {
-  return Belt_Array.reduce(x, 0, add);
-}
-
-eq("File \"bs_array_test.res\", line 87, characters 5-12", sum(u), sum(v$5));
+eq("File \"bs_array_test.res\", line 87, characters 5-12", Belt_Array.reduce(u, 0, add), Belt_Array.reduce(v$5, 0, add));
 
 b("File \"bs_array_test.res\", line 92, characters 4-11", Caml_obj.equal(Belt_Array.range(0, 3), [
   0,
diff --git a/jscomp/test/bs_hashmap_test.js b/jscomp/test/bs_hashmap_test.js
index 41e07fbb6e..e44cd0452e 100644
--- a/jscomp/test/bs_hashmap_test.js
+++ b/jscomp/test/bs_hashmap_test.js
@@ -9,6 +9,7 @@ let Belt_Array = require("../../lib/js/belt_Array.js");
 let Belt_HashMap = require("../../lib/js/belt_HashMap.js");
 let Belt_SortArray = require("../../lib/js/belt_SortArray.js");
 let Array_data_util = require("./array_data_util.js");
+let Belt_internalBucketsType = require("../../lib/js/belt_internalBucketsType.js");
 
 let suites = {
   contents: /* [] */0
@@ -30,15 +31,13 @@ function eq(x, y) {
   return x === y;
 }
 
-function hash(x) {
-  return Hashtbl.hash(x);
-}
+let hash = Hashtbl.hash;
 
 let cmp = Caml.int_compare;
 
 let Y = Belt_Id.hashable(hash, eq);
 
-let empty = Belt_HashMap.make(30, Y);
+let empty = Belt_internalBucketsType.make(Y.hash, Y.eq, 30);
 
 function add(prim0, prim1) {
   return prim0 + prim1 | 0;
@@ -79,7 +78,7 @@ eqx("File \"bs_hashmap_test.res\", line 42, characters 6-13", Belt_SortArray.sta
 
 let u$1 = Belt_Array.concat(Array_data_util.randomRange(0, 100000), Array_data_util.randomRange(0, 100));
 
-let v$1 = Belt_HashMap.make(40, Y);
+let v$1 = Belt_internalBucketsType.make(Y.hash, Y.eq, 40);
 
 Belt_HashMap.mergeMany(v$1, Belt_Array.zip(u$1, u$1));
 
diff --git a/jscomp/test/bs_hashset_int_test.js b/jscomp/test/bs_hashset_int_test.js
index c7647d3d44..3abb87e389 100644
--- a/jscomp/test/bs_hashset_int_test.js
+++ b/jscomp/test/bs_hashset_int_test.js
@@ -7,6 +7,7 @@ let Belt_SetInt = require("../../lib/js/belt_SetInt.js");
 let Array_data_util = require("./array_data_util.js");
 let Belt_HashSetInt = require("../../lib/js/belt_HashSetInt.js");
 let Belt_SortArrayInt = require("../../lib/js/belt_SortArrayInt.js");
+let Belt_internalBucketsType = require("../../lib/js/belt_internalBucketsType.js");
 
 let suites = {
   contents: /* [] */0
@@ -54,7 +55,7 @@ eq("File \"bs_hashset_int_test.res\", line 25, characters 5-12", sum2(v), 6825);
 
 let u$1 = Belt_Array.concat(Array_data_util.randomRange(0, 100000), Array_data_util.randomRange(0, 100));
 
-let v$1 = Belt_HashSetInt.make(40);
+let v$1 = Belt_internalBucketsType.make(undefined, undefined, 40);
 
 Belt_HashSetInt.mergeMany(v$1, u$1);
 
diff --git a/jscomp/test/bs_hashtbl_string_test.js b/jscomp/test/bs_hashtbl_string_test.js
index ab60ab5044..7b5b7014be 100644
--- a/jscomp/test/bs_hashtbl_string_test.js
+++ b/jscomp/test/bs_hashtbl_string_test.js
@@ -10,6 +10,7 @@ let Belt_HashMapInt = require("../../lib/js/belt_HashMapInt.js");
 let Belt_HashSetInt = require("../../lib/js/belt_HashSetInt.js");
 let Belt_HashMapString = require("../../lib/js/belt_HashMapString.js");
 let Caml_hash_primitive = require("../../lib/js/caml_hash_primitive.js");
+let Belt_internalBucketsType = require("../../lib/js/belt_internalBucketsType.js");
 
 function hash_string(s) {
   return Caml_hash_primitive.hash_final_mix(Caml_hash_primitive.hash_mix_string(0, s));
@@ -42,7 +43,7 @@ let Int = Belt_Id.hashable(Hashtbl.hash, (function (x, y) {
   return x === y;
 }));
 
-let empty = Belt_HashMap.make(500000, Int);
+let empty = Belt_internalBucketsType.make(Int.hash, Int.eq, 500000);
 
 function bench() {
   for(let i = 0; i <= 1000000; ++i){
@@ -67,7 +68,7 @@ function bench() {
 }
 
 function bench2(m) {
-  let empty = Belt_HashMap.make(1000000, m);
+  let empty = Belt_internalBucketsType.make(m.hash, m.eq, 1000000);
   for(let i = 0; i <= 1000000; ++i){
     Belt_HashMap.set(empty, String(i), i);
   }
@@ -147,7 +148,7 @@ function bench3(m) {
 let Sx = Belt_Id.comparable(Caml.string_compare);
 
 function bench4() {
-  let table = Belt_HashMapString.make(1000000);
+  let table = Belt_internalBucketsType.make(undefined, undefined, 1000000);
   for(let i = 0; i <= 1000000; ++i){
     Belt_HashMapString.set(table, String(i), i);
   }
@@ -185,7 +186,7 @@ function bench4() {
 }
 
 function bench5() {
-  let table = Belt_HashMap.make(1000000, Int);
+  let table = Belt_internalBucketsType.make(Int.hash, Int.eq, 1000000);
   console.time("bs_hashtbl_string_test.res 112");
   for(let i = 0; i <= 1000000; ++i){
     Belt_HashMap.set(table, i, i);
@@ -229,7 +230,7 @@ function bench5() {
 }
 
 function bench6() {
-  let table = Belt_HashMapInt.make(1000000);
+  let table = Belt_internalBucketsType.make(undefined, undefined, 1000000);
   for(let i = 0; i <= 1000000; ++i){
     Belt_HashMapInt.set(table, i, i);
   }
@@ -267,7 +268,7 @@ function bench6() {
 }
 
 function bench7() {
-  let table = Belt_HashSetInt.make(2000000);
+  let table = Belt_internalBucketsType.make(undefined, undefined, 2000000);
   for(let i = 0; i <= 1000000; ++i){
     Belt_HashSetInt.add(table, i);
   }
diff --git a/jscomp/test/bs_list_test.js b/jscomp/test/bs_list_test.js
index 52d626d882..3d5f260957 100644
--- a/jscomp/test/bs_list_test.js
+++ b/jscomp/test/bs_list_test.js
@@ -110,11 +110,7 @@ eq("File \"bs_list_test.res\", line 33, characters 5-12", Belt_List.getBy({
   return x % 5 === 0;
 })), undefined);
 
-function $eq$tilde(extra, extra$1) {
-  return eq("FLATTEN", extra, extra$1);
-}
-
-$eq$tilde(Belt_List.flatten({
+eq("FLATTEN", Belt_List.flatten({
   hd: {
     hd: 1,
     tl: /* [] */0
@@ -163,9 +159,9 @@ $eq$tilde(Belt_List.flatten({
   }
 });
 
-$eq$tilde(Belt_List.flatten(/* [] */0), /* [] */0);
+eq("FLATTEN", Belt_List.flatten(/* [] */0), /* [] */0);
 
-$eq$tilde(Belt_List.flatten({
+eq("FLATTEN", Belt_List.flatten({
   hd: /* [] */0,
   tl: {
     hd: /* [] */0,
@@ -203,11 +199,7 @@ $eq$tilde(Belt_List.flatten({
   }
 });
 
-function $eq$tilde$1(extra, extra$1) {
-  return eq("CONCATMANY", extra, extra$1);
-}
-
-$eq$tilde$1(Belt_List.concatMany([
+eq("CONCATMANY", Belt_List.concatMany([
   {
     hd: 1,
     tl: /* [] */0
@@ -247,9 +239,9 @@ $eq$tilde$1(Belt_List.concatMany([
   }
 });
 
-$eq$tilde$1(Belt_List.concatMany([]), /* [] */0);
+eq("CONCATMANY", Belt_List.concatMany([]), /* [] */0);
 
-$eq$tilde$1(Belt_List.concatMany([
+eq("CONCATMANY", Belt_List.concatMany([
   /* [] */0,
   /* [] */0,
   {
@@ -276,7 +268,7 @@ $eq$tilde$1(Belt_List.concatMany([
   }
 });
 
-$eq$tilde$1(Belt_List.concatMany([
+eq("CONCATMANY", Belt_List.concatMany([
   /* [] */0,
   /* [] */0,
   {
@@ -309,7 +301,7 @@ $eq$tilde$1(Belt_List.concatMany([
   }
 });
 
-$eq$tilde$1(Belt_List.concatMany([{
+eq("CONCATMANY", Belt_List.concatMany([{
     hd: 1,
     tl: {
       hd: 2,
@@ -339,11 +331,7 @@ eq("File \"bs_list_test.res\", line 66, characters 2-9", Belt_List.toArray(Belt_
   return i;
 }))));
 
-function $eq$tilde$2(extra, extra$1) {
-  return eq("APPEND", extra, extra$1);
-}
-
-$eq$tilde$2(Belt_List.concat({
+eq("APPEND", Belt_List.concat({
   hd: 1,
   tl: /* [] */0
 }, /* [] */0), {
@@ -351,7 +339,7 @@ $eq$tilde$2(Belt_List.concat({
   tl: /* [] */0
 });
 
-$eq$tilde$2(Belt_List.concat(/* [] */0, {
+eq("APPEND", Belt_List.concat(/* [] */0, {
   hd: 1,
   tl: /* [] */0
 }), {
@@ -359,11 +347,7 @@ $eq$tilde$2(Belt_List.concat(/* [] */0, {
   tl: /* [] */0
 });
 
-function $eq$tilde$3(extra, extra$1) {
-  return eq("ZIP", extra, extra$1);
-}
-
-$eq$tilde$3(Belt_List.zip({
+eq("ZIP", Belt_List.zip({
   hd: 1,
   tl: {
     hd: 2,
@@ -392,14 +376,14 @@ $eq$tilde$3(Belt_List.zip({
   }
 });
 
-$eq$tilde$3(Belt_List.zip(/* [] */0, {
+eq("ZIP", Belt_List.zip(/* [] */0, {
   hd: 1,
   tl: /* [] */0
 }), /* [] */0);
 
-$eq$tilde$3(Belt_List.zip(/* [] */0, /* [] */0), /* [] */0);
+eq("ZIP", Belt_List.zip(/* [] */0, /* [] */0), /* [] */0);
 
-$eq$tilde$3(Belt_List.zip({
+eq("ZIP", Belt_List.zip({
   hd: 1,
   tl: {
     hd: 2,
@@ -410,7 +394,7 @@ $eq$tilde$3(Belt_List.zip({
   }
 }, /* [] */0), /* [] */0);
 
-$eq$tilde$3(Belt_List.zip({
+eq("ZIP", Belt_List.zip({
   hd: 1,
   tl: {
     hd: 2,
@@ -456,11 +440,7 @@ function evenIndex(_x, i) {
   return i % 2 === 0;
 }
 
-function $eq$tilde$4(extra, extra$1) {
-  return eq("PARTITION", extra, extra$1);
-}
-
-$eq$tilde$4(Belt_List.partition({
+eq("PARTITION", Belt_List.partition({
   hd: 1,
   tl: {
     hd: 2,
@@ -501,7 +481,7 @@ $eq$tilde$4(Belt_List.partition({
   }
 ]);
 
-$eq$tilde$4(Belt_List.partition({
+eq("PARTITION", Belt_List.partition({
   hd: 2,
   tl: {
     hd: 2,
@@ -530,7 +510,7 @@ $eq$tilde$4(Belt_List.partition({
   /* [] */0
 ]);
 
-$eq$tilde$4(Belt_List.partition({
+eq("PARTITION", Belt_List.partition({
   hd: 2,
   tl: {
     hd: 2,
@@ -561,21 +541,17 @@ $eq$tilde$4(Belt_List.partition({
   }
 ]);
 
-$eq$tilde$4(Belt_List.partition(/* [] */0, mod2), [
+eq("PARTITION", Belt_List.partition(/* [] */0, mod2), [
   /* [] */0,
   /* [] */0
 ]);
 
-function $eq$tilde$5(extra, extra$1) {
-  return eq("UNZIP", extra, extra$1);
-}
-
-$eq$tilde$5(Belt_List.unzip(/* [] */0), [
+eq("UNZIP", Belt_List.unzip(/* [] */0), [
   /* [] */0,
   /* [] */0
 ]);
 
-$eq$tilde$5(Belt_List.unzip({
+eq("UNZIP", Belt_List.unzip({
   hd: [
     1,
     2
@@ -592,7 +568,7 @@ $eq$tilde$5(Belt_List.unzip({
   }
 ]);
 
-$eq$tilde$5(Belt_List.unzip({
+eq("UNZIP", Belt_List.unzip({
   hd: [
     1,
     2
@@ -621,11 +597,7 @@ $eq$tilde$5(Belt_List.unzip({
   }
 ]);
 
-function $eq$tilde$6(extra, extra$1) {
-  return eq("FILTER", extra, extra$1);
-}
-
-$eq$tilde$6(Belt_List.keep({
+eq("FILTER", Belt_List.keep({
   hd: 1,
   tl: {
     hd: 2,
@@ -645,7 +617,7 @@ $eq$tilde$6(Belt_List.keep({
   }
 });
 
-$eq$tilde$6(Belt_List.keep({
+eq("FILTER", Belt_List.keep({
   hd: 1,
   tl: {
     hd: 3,
@@ -656,9 +628,9 @@ $eq$tilde$6(Belt_List.keep({
   }
 }, mod2), /* [] */0);
 
-$eq$tilde$6(Belt_List.keep(/* [] */0, mod2), /* [] */0);
+eq("FILTER", Belt_List.keep(/* [] */0, mod2), /* [] */0);
 
-$eq$tilde$6(Belt_List.keep({
+eq("FILTER", Belt_List.keep({
   hd: 2,
   tl: {
     hd: 2,
@@ -690,13 +662,9 @@ $eq$tilde$6(Belt_List.keep({
   }
 });
 
-function $eq$tilde$7(extra, extra$1) {
-  return eq("FILTER2", extra, extra$1);
-}
-
-$eq$tilde$7(Belt_List.keepWithIndex(/* [] */0, evenIndex), /* [] */0);
+eq("FILTER2", Belt_List.keepWithIndex(/* [] */0, evenIndex), /* [] */0);
 
-$eq$tilde$7(Belt_List.keepWithIndex({
+eq("FILTER2", Belt_List.keepWithIndex({
   hd: 1,
   tl: {
     hd: 2,
@@ -716,7 +684,7 @@ $eq$tilde$7(Belt_List.keepWithIndex({
   }
 });
 
-$eq$tilde$7(Belt_List.keepWithIndex({
+eq("FILTER2", Belt_List.keepWithIndex({
   hd: 0,
   tl: {
     hd: 1,
@@ -758,11 +726,7 @@ function id(x) {
   return x;
 }
 
-function $eq$tilde$8(extra, extra$1) {
-  return eq("MAP", extra, extra$1);
-}
-
-$eq$tilde$8(Belt_List.map(Belt_List.makeBy(5, id), (function (x) {
+eq("MAP", Belt_List.map(Belt_List.makeBy(5, id), (function (x) {
   return (x << 1);
 })), {
   hd: 0,
@@ -781,9 +745,9 @@ $eq$tilde$8(Belt_List.map(Belt_List.makeBy(5, id), (function (x) {
   }
 });
 
-$eq$tilde$8(Belt_List.map(/* [] */0, id), /* [] */0);
+eq("MAP", Belt_List.map(/* [] */0, id), /* [] */0);
 
-$eq$tilde$8(Belt_List.map({
+eq("MAP", Belt_List.map({
   hd: 1,
   tl: /* [] */0
 }, (function (x) {
@@ -801,33 +765,25 @@ let length_10_id = Belt_List.makeBy(10, id);
 
 let length_8_id = Belt_List.makeBy(8, id);
 
-function $eq$tilde$9(extra, extra$1) {
-  return eq("MAP2", extra, extra$1);
-}
-
 let d = Belt_List.makeBy(10, (function (x) {
   return (x << 1);
 }));
 
-function map2_add(x, y) {
-  return Belt_List.zipBy(x, y, add);
-}
-
-$eq$tilde$9(map2_add(length_10_id, length_10_id), d);
+eq("MAP2", Belt_List.zipBy(length_10_id, length_10_id, add), d);
 
-$eq$tilde$9(map2_add(/* [] */0, {
+eq("MAP2", Belt_List.zipBy(/* [] */0, {
   hd: 1,
   tl: /* [] */0
-}), /* [] */0);
+}, add), /* [] */0);
 
-$eq$tilde$9(map2_add({
+eq("MAP2", Belt_List.zipBy({
   hd: 1,
   tl: /* [] */0
-}, /* [] */0), /* [] */0);
+}, /* [] */0, add), /* [] */0);
 
-$eq$tilde$9(map2_add(/* [] */0, /* [] */0), /* [] */0);
+eq("MAP2", Belt_List.zipBy(/* [] */0, /* [] */0, add), /* [] */0);
 
-$eq$tilde$9(map2_add(length_10_id, length_10_id), Belt_List.concat(Belt_List.map(length_8_id, (function (x) {
+eq("MAP2", Belt_List.zipBy(length_10_id, length_10_id, add), Belt_List.concat(Belt_List.map(length_8_id, (function (x) {
   return (x << 1);
 })), {
   hd: 16,
@@ -837,11 +793,11 @@ $eq$tilde$9(map2_add(length_10_id, length_10_id), Belt_List.concat(Belt_List.map
   }
 }));
 
-$eq$tilde$9(map2_add(length_10_id, length_8_id), Belt_List.mapWithIndex(length_8_id, (function (i, x) {
+eq("MAP2", Belt_List.zipBy(length_10_id, length_8_id, add), Belt_List.mapWithIndex(length_8_id, (function (i, x) {
   return i + x | 0;
 })));
 
-$eq$tilde$9(Belt_List.reverse(Belt_List.mapReverse2(length_10_id, length_10_id, add)), Belt_List.map(length_10_id, (function (x) {
+eq("MAP2", Belt_List.reverse(Belt_List.mapReverse2(length_10_id, length_10_id, add)), Belt_List.map(length_10_id, (function (x) {
   return (x << 1);
 })));
 
@@ -849,9 +805,9 @@ let xs = Belt_List.reverse(Belt_List.mapReverse2(length_8_id, length_10_id, add)
 
 eq("File \"bs_list_test.res\", line 163, characters 5-12", Belt_List.length(xs), 8);
 
-$eq$tilde$9(xs, Belt_List.zipBy(length_10_id, length_8_id, add));
+eq("MAP2", xs, Belt_List.zipBy(length_10_id, length_8_id, add));
 
-$eq$tilde$9(Belt_List.mapReverse2({
+eq("MAP2", Belt_List.mapReverse2({
   hd: 1,
   tl: {
     hd: 2,
@@ -876,11 +832,7 @@ $eq$tilde$9(Belt_List.mapReverse2({
   }
 });
 
-function $eq$tilde$10(extra, extra$1) {
-  return eq("TAKE", extra, extra$1);
-}
-
-$eq$tilde$10(Belt_List.take({
+eq("TAKE", Belt_List.take({
   hd: 1,
   tl: {
     hd: 2,
@@ -897,9 +849,9 @@ $eq$tilde$10(Belt_List.take({
   }
 });
 
-$eq$tilde$10(Belt_List.take(/* [] */0, 1), undefined);
+eq("TAKE", Belt_List.take(/* [] */0, 1), undefined);
 
-$eq$tilde$10(Belt_List.take({
+eq("TAKE", Belt_List.take({
   hd: 1,
   tl: {
     hd: 2,
@@ -907,7 +859,7 @@ $eq$tilde$10(Belt_List.take({
   }
 }, 3), undefined);
 
-$eq$tilde$10(Belt_List.take({
+eq("TAKE", Belt_List.take({
   hd: 1,
   tl: {
     hd: 2,
@@ -921,19 +873,15 @@ $eq$tilde$10(Belt_List.take({
   }
 });
 
-$eq$tilde$10(Belt_List.take(length_10_id, 8), length_8_id);
+eq("TAKE", Belt_List.take(length_10_id, 8), length_8_id);
 
-$eq$tilde$10(Belt_List.take(length_10_id, 0), /* [] */0);
+eq("TAKE", Belt_List.take(length_10_id, 0), /* [] */0);
 
-$eq$tilde$10(Belt_List.take(length_8_id, -2), undefined);
+eq("TAKE", Belt_List.take(length_8_id, -2), undefined);
 
-function $eq$tilde$11(extra, extra$1) {
-  return eq("DROP", extra, extra$1);
-}
-
-$eq$tilde$11(Belt_List.drop(length_10_id, 10), /* [] */0);
+eq("DROP", Belt_List.drop(length_10_id, 10), /* [] */0);
 
-$eq$tilde$11(Belt_List.drop(length_10_id, 8), {
+eq("DROP", Belt_List.drop(length_10_id, 8), {
   hd: 8,
   tl: {
     hd: 9,
@@ -941,26 +889,22 @@ $eq$tilde$11(Belt_List.drop(length_10_id, 8), {
   }
 });
 
-$eq$tilde$11(Belt_List.drop(length_10_id, 0), length_10_id);
+eq("DROP", Belt_List.drop(length_10_id, 0), length_10_id);
 
-$eq$tilde$11(Belt_List.drop(length_8_id, -1), undefined);
-
-function $eq$tilde$12(extra, extra$1) {
-  return eq("SPLIT", extra, extra$1);
-}
+eq("DROP", Belt_List.drop(length_8_id, -1), undefined);
 
 let a = Belt_List.makeBy(5, id);
 
-$eq$tilde$12(Belt_List.splitAt(/* [] */0, 1), undefined);
+eq("SPLIT", Belt_List.splitAt(/* [] */0, 1), undefined);
 
-$eq$tilde$12(Belt_List.splitAt(a, 6), undefined);
+eq("SPLIT", Belt_List.splitAt(a, 6), undefined);
 
-$eq$tilde$12(Belt_List.splitAt(a, 5), [
+eq("SPLIT", Belt_List.splitAt(a, 5), [
   a,
   /* [] */0
 ]);
 
-$eq$tilde$12(Belt_List.splitAt(a, 4), [
+eq("SPLIT", Belt_List.splitAt(a, 4), [
   {
     hd: 0,
     tl: {
@@ -980,7 +924,7 @@ $eq$tilde$12(Belt_List.splitAt(a, 4), [
   }
 ]);
 
-$eq$tilde$12(Belt_List.splitAt(a, 3), [
+eq("SPLIT", Belt_List.splitAt(a, 3), [
   {
     hd: 0,
     tl: {
@@ -1000,7 +944,7 @@ $eq$tilde$12(Belt_List.splitAt(a, 3), [
   }
 ]);
 
-$eq$tilde$12(Belt_List.splitAt(a, 2), [
+eq("SPLIT", Belt_List.splitAt(a, 2), [
   {
     hd: 0,
     tl: {
@@ -1020,7 +964,7 @@ $eq$tilde$12(Belt_List.splitAt(a, 2), [
   }
 ]);
 
-$eq$tilde$12(Belt_List.splitAt(a, 1), [
+eq("SPLIT", Belt_List.splitAt(a, 1), [
   {
     hd: 0,
     tl: /* [] */0
@@ -1040,21 +984,17 @@ $eq$tilde$12(Belt_List.splitAt(a, 1), [
   }
 ]);
 
-$eq$tilde$12(Belt_List.splitAt(a, 0), [
+eq("SPLIT", Belt_List.splitAt(a, 0), [
   /* [] */0,
   a
 ]);
 
-$eq$tilde$12(Belt_List.splitAt(a, -1), undefined);
+eq("SPLIT", Belt_List.splitAt(a, -1), undefined);
 
 function succx(x) {
   return x + 1 | 0;
 }
 
-function $eq$tilde$13(extra, extra$1) {
-  return eq("REMOVEASSOQ", extra, extra$1);
-}
-
 function eqx(x, y) {
   return x === y;
 }
@@ -1125,7 +1065,7 @@ b("File \"bs_list_test.res\", line 207, characters 4-11", Belt_List.hasAssoc({
   return (x + 1 | 0) === y;
 })));
 
-$eq$tilde$13(Belt_List.removeAssoc({
+eq("REMOVEASSOQ", Belt_List.removeAssoc({
   hd: [
     1,
     "1"
@@ -1159,7 +1099,7 @@ $eq$tilde$13(Belt_List.removeAssoc({
   }
 });
 
-$eq$tilde$13(Belt_List.removeAssoc({
+eq("REMOVEASSOQ", Belt_List.removeAssoc({
   hd: [
     1,
     "1"
@@ -1193,7 +1133,7 @@ $eq$tilde$13(Belt_List.removeAssoc({
   }
 });
 
-$eq$tilde$13(Belt_List.removeAssoc({
+eq("REMOVEASSOQ", Belt_List.removeAssoc({
   hd: [
     1,
     "1"
@@ -1227,7 +1167,7 @@ $eq$tilde$13(Belt_List.removeAssoc({
   }
 });
 
-$eq$tilde$13(Belt_List.removeAssoc({
+eq("REMOVEASSOQ", Belt_List.removeAssoc({
   hd: [
     1,
     "1"
@@ -1267,7 +1207,7 @@ $eq$tilde$13(Belt_List.removeAssoc({
   }
 });
 
-$eq$tilde$13(Belt_List.removeAssoc({
+eq("REMOVEASSOQ", Belt_List.removeAssoc({
   hd: [
     1,
     "1"
@@ -1299,7 +1239,7 @@ $eq$tilde$13(Belt_List.removeAssoc({
   }
 });
 
-$eq$tilde$13(Belt_List.removeAssoc({
+eq("REMOVEASSOQ", Belt_List.removeAssoc({
   hd: [
     1,
     "1"
@@ -1331,7 +1271,7 @@ $eq$tilde$13(Belt_List.removeAssoc({
   }
 });
 
-$eq$tilde$13(Belt_List.removeAssoc({
+eq("REMOVEASSOQ", Belt_List.removeAssoc({
   hd: [
     1,
     "1"
@@ -1363,7 +1303,7 @@ $eq$tilde$13(Belt_List.removeAssoc({
   }
 });
 
-$eq$tilde$13(Belt_List.removeAssoc(/* [] */0, 2, eqx), /* [] */0);
+eq("REMOVEASSOQ", Belt_List.removeAssoc(/* [] */0, 2, eqx), /* [] */0);
 
 let ll = {
   hd: [
@@ -2354,15 +2294,11 @@ makeTest(2);
 
 makeTest(3);
 
-function $eq$tilde$14(extra, extra$1) {
-  return eq("SORT", extra, extra$1);
-}
-
 function cmp(a, b) {
   return a - b | 0;
 }
 
-$eq$tilde$14(Belt_List.sort({
+eq("SORT", Belt_List.sort({
   hd: 5,
   tl: {
     hd: 4,
@@ -2388,7 +2324,7 @@ $eq$tilde$14(Belt_List.sort({
   }
 });
 
-$eq$tilde$14(Belt_List.sort({
+eq("SORT", Belt_List.sort({
   hd: 3,
   tl: {
     hd: 9,
diff --git a/jscomp/test/bs_map_set_dict_test.js b/jscomp/test/bs_map_set_dict_test.js
index c3b367a6f5..0f22228a21 100644
--- a/jscomp/test/bs_map_set_dict_test.js
+++ b/jscomp/test/bs_map_set_dict_test.js
@@ -65,7 +65,7 @@ let m2 = {
   data: undefined
 };
 
-let data = undefined;
+let data;
 
 Belt_Map.getId(m2);
 
@@ -75,11 +75,13 @@ for(let i = 0; i <= 100000; ++i){
   data = Belt_MapDict.set(data, i, i, m_dict.cmp);
 }
 
+let data$1 = data;
+
 let newm_cmp = m_dict.cmp;
 
 let newm = {
   cmp: newm_cmp,
-  data: data
+  data: data$1
 };
 
 console.log(newm);
@@ -92,13 +94,13 @@ let m_dict$1 = Belt_Map.getId(m);
 
 let cmp = m_dict$1.cmp;
 
-let data$1 = undefined;
+let data$2;
 
 for(let i$1 = 0; i$1 <= 100000; ++i$1){
-  data$1 = Belt_SetDict.add(data$1, i$1, cmp);
+  data$2 = Belt_SetDict.add(data$2, i$1, cmp);
 }
 
-console.log(data$1);
+console.log(data$2);
 
 function f(none) {
   return Belt_Map.fromArray(none, Icmp);
@@ -110,14 +112,12 @@ function $eq$tilde(a, b) {
   };
 }
 
-let none = Belt_Array.map(Array_data_util.randomRange(0, 39), (function (x) {
+let u0 = Belt_Map.fromArray(Belt_Array.map(Array_data_util.randomRange(0, 39), (function (x) {
   return [
     x,
     x
   ];
-}));
-
-let u0 = Belt_Map.fromArray(none, Icmp);
+})), Icmp);
 
 let u1 = Belt_Map.set(u0, 39, 120);
 
@@ -151,14 +151,12 @@ eq("File \"bs_map_set_dict_test.res\", line 84, characters 5-12", Belt_Map.get(u
 
 eq("File \"bs_map_set_dict_test.res\", line 85, characters 5-12", Belt_Map.get(u1, 39), 120);
 
-let none$1 = Belt_Array.makeByAndShuffle(10000, (function (x) {
+let u = Belt_Map.fromArray(Belt_Array.makeByAndShuffle(10000, (function (x) {
   return [
     x,
     x
   ];
-}));
-
-let u = Belt_Map.fromArray(none$1, Icmp);
+})), Icmp);
 
 eq("File \"bs_map_set_dict_test.res\", line 90, characters 5-12", Belt_Array.makeBy(10000, (function (x) {
   return [
diff --git a/jscomp/test/bs_map_test.js b/jscomp/test/bs_map_test.js
index dd79a0faba..689645a29f 100644
--- a/jscomp/test/bs_map_test.js
+++ b/jscomp/test/bs_map_test.js
@@ -47,13 +47,9 @@ function b(loc, v) {
   };
 }
 
-function mapOfArray(x) {
-  return Belt_MapInt.fromArray(x);
-}
+let mapOfArray = Belt_MapInt.fromArray;
 
-function setOfArray(x) {
-  return Belt_SetInt.fromArray(x);
-}
+let setOfArray = Belt_SetInt.fromArray;
 
 function emptyMap() {
   
diff --git a/jscomp/test/bs_mutable_set_test.js b/jscomp/test/bs_mutable_set_test.js
index 615216b6a4..16d171bb1f 100644
--- a/jscomp/test/bs_mutable_set_test.js
+++ b/jscomp/test/bs_mutable_set_test.js
@@ -55,7 +55,7 @@ for(let i = 0 ,i_finish = r.length; i < i_finish; ++i){
   Belt_MutableSetInt.remove(u, r[i]);
 }
 
-b("File \"bs_mutable_set_test.res\", line 33, characters 8-15", u.data === undefined);
+b("File \"bs_mutable_set_test.res\", line 33, characters 8-15", Belt_MutableSetInt.isEmpty(u));
 
 Belt_MutableSetInt.add(u, 0);
 
@@ -67,13 +67,13 @@ Belt_MutableSetInt.add(u, 0);
 
 eq("File \"bs_mutable_set_test.res\", line 38, characters 9-16", Belt_internalAVLset.size(u.data), 3);
 
-b("File \"bs_mutable_set_test.res\", line 39, characters 8-15", u.data !== undefined);
+b("File \"bs_mutable_set_test.res\", line 39, characters 8-15", !Belt_MutableSetInt.isEmpty(u));
 
 for(let i$1 = 0; i$1 <= 3; ++i$1){
   Belt_MutableSetInt.remove(u, i$1);
 }
 
-b("File \"bs_mutable_set_test.res\", line 43, characters 8-15", u.data === undefined);
+b("File \"bs_mutable_set_test.res\", line 43, characters 8-15", Belt_MutableSetInt.isEmpty(u));
 
 Belt_MutableSetInt.mergeMany(u, Array_data_util.randomRange(0, 20000));
 
@@ -101,11 +101,11 @@ Belt_MutableSetInt.removeMany(u, Array_data_util.randomRange(10000, 19999));
 
 eq("File \"bs_mutable_set_test.res\", line 56, characters 9-16", Belt_internalAVLset.size(u.data), 1);
 
-b("File \"bs_mutable_set_test.res\", line 57, characters 8-15", Belt_MutableSetInt.has(u, 20000));
+b("File \"bs_mutable_set_test.res\", line 57, characters 8-15", Belt_internalSetInt.has(u.data, 20000));
 
 Belt_MutableSetInt.removeMany(u, Array_data_util.randomRange(10000, 30000));
 
-b("File \"bs_mutable_set_test.res\", line 59, characters 8-15", u.data === undefined);
+b("File \"bs_mutable_set_test.res\", line 59, characters 8-15", Belt_MutableSetInt.isEmpty(u));
 
 let xs$1 = Array_data_util.randomRange(1000, 2000);
 
@@ -145,11 +145,9 @@ eq("File \"bs_mutable_set_test.res\", line 82, characters 9-16", indeedAded, 100
 
 eq("File \"bs_mutable_set_test.res\", line 83, characters 9-16", Belt_internalAVLset.size(v.data), 1501);
 
-let d = {
+b("File \"bs_mutable_set_test.res\", line 84, characters 8-15", Belt_MutableSetInt.isEmpty({
   data: undefined
-};
-
-b("File \"bs_mutable_set_test.res\", line 84, characters 8-15", d.data === undefined);
+}));
 
 eq("File \"bs_mutable_set_test.res\", line 85, characters 9-16", Belt_internalAVLset.minimum(v.data), 500);
 
@@ -173,9 +171,9 @@ eq("File \"bs_mutable_set_test.res\", line 91, characters 9-16", Belt_internalAV
 
 Belt_internalAVLset.checkInvariantInternal(v.data);
 
-eq("File \"bs_mutable_set_test.res\", line 93, characters 9-16", Belt_MutableSetInt.get(v, 3), undefined);
+eq("File \"bs_mutable_set_test.res\", line 93, characters 9-16", Belt_internalSetInt.get(v.data, 3), undefined);
 
-eq("File \"bs_mutable_set_test.res\", line 94, characters 9-16", Belt_MutableSetInt.get(v, 1200), 1200);
+eq("File \"bs_mutable_set_test.res\", line 94, characters 9-16", Belt_internalSetInt.get(v.data, 1200), 1200);
 
 let match = Belt_MutableSetInt.split(v, 1000);
 
@@ -199,9 +197,7 @@ b("File \"bs_mutable_set_test.res\", line 99, characters 8-15", Belt_MutableSetI
 
 b("File \"bs_mutable_set_test.res\", line 100, characters 8-15", Belt_MutableSetInt.subset(bb, v));
 
-let d$1 = Belt_MutableSetInt.intersect(aa, bb);
-
-b("File \"bs_mutable_set_test.res\", line 101, characters 8-15", d$1.data === undefined);
+b("File \"bs_mutable_set_test.res\", line 101, characters 8-15", Belt_MutableSetInt.isEmpty(Belt_MutableSetInt.intersect(aa, bb)));
 
 let c = Belt_MutableSetInt.removeCheck(v, 1000);
 
@@ -229,9 +225,7 @@ b("File \"bs_mutable_set_test.res\", line 108, characters 8-15", Belt_MutableSet
 
 b("File \"bs_mutable_set_test.res\", line 109, characters 8-15", Belt_MutableSetInt.subset(bb$1, v));
 
-let d$2 = Belt_MutableSetInt.intersect(aa$1, bb$1);
-
-b("File \"bs_mutable_set_test.res\", line 110, characters 8-15", d$2.data === undefined);
+b("File \"bs_mutable_set_test.res\", line 110, characters 8-15", Belt_MutableSetInt.isEmpty(Belt_MutableSetInt.intersect(aa$1, bb$1)));
 
 let xs$2 = Array_data_util.randomRange(0, 100);
 
@@ -434,7 +428,7 @@ for(let i$2 = 0; i$2 <= 100000; ++i$2){
 Belt_internalAVLset.checkInvariantInternal(v$1.data);
 
 b("File \"bs_mutable_set_test.res\", line 188, characters 10-17", Belt_Range.every(0, 100000, (function (i) {
-  return Belt_MutableSetInt.has(v$1, i);
+  return Belt_internalSetInt.has(v$1.data, i);
 })));
 
 eq("File \"bs_mutable_set_test.res\", line 189, characters 5-12", Belt_internalAVLset.size(v$1.data), 100001);
@@ -475,7 +469,7 @@ for(let i$4 = 0 ,i_finish$2 = vv.length; i$4 < i_finish$2; ++i$4){
 
 eq("File \"bs_mutable_set_test.res\", line 216, characters 5-12", Belt_internalAVLset.size(v$3.data), 0);
 
-b("File \"bs_mutable_set_test.res\", line 217, characters 4-11", v$3.data === undefined);
+b("File \"bs_mutable_set_test.res\", line 217, characters 4-11", Belt_MutableSetInt.isEmpty(v$3));
 
 let xs$25 = Belt_Array.makeBy(30, (function (i) {
   return i;
@@ -658,11 +652,11 @@ let xs$30 = Belt_Array.map(Array_data_util.randomRange(0, 1000), (function (x) {
   return (x << 1);
 }));
 
-let d$3 = {
+let d = {
   data: Belt_internalSetInt.fromArray(xs$30)
 };
 
-let match$8 = Belt_MutableSetInt.split(d$3, 1001);
+let match$8 = Belt_MutableSetInt.split(d, 1001);
 
 let match$9 = match$8[0];
 
diff --git a/jscomp/test/bs_poly_map_test.js b/jscomp/test/bs_poly_map_test.js
index 0865fa4cc5..d0aaf258eb 100644
--- a/jscomp/test/bs_poly_map_test.js
+++ b/jscomp/test/bs_poly_map_test.js
@@ -51,8 +51,7 @@ function mergeInter(s1, s2) {
     }
     
   }));
-  let x = Belt_MapDict.keysToArray(m.data);
-  return Belt_Set.fromArray(x, Icmp);
+  return Belt_Set.fromArray(Belt_MapDict.keysToArray(m.data), Icmp);
 }
 
 function mergeUnion(s1, s2) {
@@ -62,8 +61,7 @@ function mergeUnion(s1, s2) {
     }
     
   }));
-  let x = Belt_MapDict.keysToArray(m.data);
-  return Belt_Set.fromArray(x, Icmp);
+  return Belt_Set.fromArray(Belt_MapDict.keysToArray(m.data), Icmp);
 }
 
 function mergeDiff(s1, s2) {
@@ -73,8 +71,7 @@ function mergeDiff(s1, s2) {
     }
     
   }));
-  let x = Belt_MapDict.keysToArray(m.data);
-  return Belt_Set.fromArray(x, Icmp);
+  return Belt_Set.fromArray(Belt_MapDict.keysToArray(m.data), Icmp);
 }
 
 function randomRange(i, j) {
@@ -86,33 +83,19 @@ function randomRange(i, j) {
   }));
 }
 
-let x = randomRange(0, 100);
-
-let u0 = Belt_Map.fromArray(x, Icmp);
-
-let x$1 = randomRange(30, 120);
-
-let u1 = Belt_Map.fromArray(x$1, Icmp);
-
-let x$2 = Array_data_util.range(30, 100);
-
-b("File \"bs_poly_map_test.res\", line 64, characters 4-11", Belt_Set.eq(mergeInter(u0, u1), Belt_Set.fromArray(x$2, Icmp)));
+let u0 = Belt_Map.fromArray(randomRange(0, 100), Icmp);
 
-let x$3 = Array_data_util.range(0, 120);
+let u1 = Belt_Map.fromArray(randomRange(30, 120), Icmp);
 
-b("File \"bs_poly_map_test.res\", line 65, characters 4-11", Belt_Set.eq(mergeUnion(u0, u1), Belt_Set.fromArray(x$3, Icmp)));
+b("File \"bs_poly_map_test.res\", line 64, characters 4-11", Belt_Set.eq(mergeInter(u0, u1), Belt_Set.fromArray(Array_data_util.range(30, 100), Icmp)));
 
-let x$4 = Array_data_util.range(0, 29);
+b("File \"bs_poly_map_test.res\", line 65, characters 4-11", Belt_Set.eq(mergeUnion(u0, u1), Belt_Set.fromArray(Array_data_util.range(0, 120), Icmp)));
 
-b("File \"bs_poly_map_test.res\", line 66, characters 4-11", Belt_Set.eq(mergeDiff(u0, u1), Belt_Set.fromArray(x$4, Icmp)));
+b("File \"bs_poly_map_test.res\", line 66, characters 4-11", Belt_Set.eq(mergeDiff(u0, u1), Belt_Set.fromArray(Array_data_util.range(0, 29), Icmp)));
 
-let x$5 = Array_data_util.range(101, 120);
+b("File \"bs_poly_map_test.res\", line 67, characters 4-11", Belt_Set.eq(mergeDiff(u1, u0), Belt_Set.fromArray(Array_data_util.range(101, 120), Icmp)));
 
-b("File \"bs_poly_map_test.res\", line 67, characters 4-11", Belt_Set.eq(mergeDiff(u1, u0), Belt_Set.fromArray(x$5, Icmp)));
-
-let x$6 = randomRange(0, 10);
-
-let a0 = Belt_Map.fromArray(x$6, Icmp);
+let a0 = Belt_Map.fromArray(randomRange(0, 10), Icmp);
 
 let a1 = Belt_Map.set(a0, 3, 33);
 
@@ -176,9 +159,7 @@ let a8 = Belt_Map.removeMany(a7, Array_data_util.randomRange(0, 100));
 
 b("File \"bs_poly_map_test.res\", line 101, characters 4-11", Belt_MapDict.isEmpty(a8.data));
 
-let x$7 = randomRange(0, 100);
-
-let u0$1 = Belt_Map.fromArray(x$7, Icmp);
+let u0$1 = Belt_Map.fromArray(randomRange(0, 100), Icmp);
 
 let u1$1 = Belt_Map.set(u0$1, 3, 32);
 
@@ -207,14 +188,12 @@ let m = {
 
 let m1 = acc(m, Belt_Array.concat(Array_data_util.randomRange(0, 20), Array_data_util.randomRange(10, 30)));
 
-let x$8 = Belt_Array.makeBy(31, (function (i) {
+b("File \"bs_poly_map_test.res\", line 126, characters 4-11", Belt_Map.eq(m1, Belt_Map.fromArray(Belt_Array.makeBy(31, (function (i) {
   return [
     i,
     i >= 10 && i <= 20 ? 2 : 1
   ];
-}));
-
-b("File \"bs_poly_map_test.res\", line 126, characters 4-11", Belt_Map.eq(m1, Belt_Map.fromArray(x$8, Icmp), (function (x, y) {
+})), Icmp), (function (x, y) {
   return x === y;
 })));
 
@@ -232,14 +211,12 @@ let v1 = Belt_Map.mergeMany(v0, Belt_Array.map(Array_data_util.randomRange(0, 10
   ];
 })));
 
-let x$9 = Belt_Array.map(Array_data_util.randomRange(0, 10000), (function (x) {
+let v2 = Belt_Map.fromArray(Belt_Array.map(Array_data_util.randomRange(0, 10000), (function (x) {
   return [
     x,
     x
   ];
-}));
-
-let v2 = Belt_Map.fromArray(x$9, Icmp);
+})), Icmp);
 
 b("File \"bs_poly_map_test.res\", line 150, characters 4-11", Belt_Map.eq(v1, v2, (function (x, y) {
   return x === y;
diff --git a/jscomp/test/bs_poly_mutable_map_test.js b/jscomp/test/bs_poly_mutable_map_test.js
index 3bbcd3dbfa..9563788e47 100644
--- a/jscomp/test/bs_poly_mutable_map_test.js
+++ b/jscomp/test/bs_poly_mutable_map_test.js
@@ -45,9 +45,7 @@ function randomRange(i, j) {
   }));
 }
 
-let x = randomRange(0, 10);
-
-let a0 = Belt_MutableMap.fromArray(x, Icmp);
+let a0 = Belt_MutableMap.fromArray(randomRange(0, 10), Icmp);
 
 Belt_MutableMap.set(a0, 3, 33);
 
@@ -74,11 +72,9 @@ eq("File \"bs_poly_mutable_map_test.res\", line 29, characters 5-12", Belt_inter
 
 Belt_MutableMap.removeMany(a0, Array_data_util.randomRange(0, 100));
 
-b("File \"bs_poly_mutable_map_test.res\", line 31, characters 4-11", a0.data === undefined);
-
-let x$1 = randomRange(0, 10000);
+b("File \"bs_poly_mutable_map_test.res\", line 31, characters 4-11", Belt_MutableMap.isEmpty(a0));
 
-let a0$1 = Belt_MutableMap.fromArray(x$1, Icmp);
+let a0$1 = Belt_MutableMap.fromArray(randomRange(0, 10000), Icmp);
 
 Belt_MutableMap.set(a0$1, 2000, 33);
 
diff --git a/jscomp/test/bs_poly_mutable_set_test.js b/jscomp/test/bs_poly_mutable_set_test.js
index 676ec6ca82..33a00591d1 100644
--- a/jscomp/test/bs_poly_mutable_set_test.js
+++ b/jscomp/test/bs_poly_mutable_set_test.js
@@ -39,9 +39,7 @@ function empty() {
   };
 }
 
-let none = Array_data_util.range(0, 30);
-
-let u = Belt_MutableSet.fromArray(none, IntCmp);
+let u = Belt_MutableSet.fromArray(Array_data_util.range(0, 30), IntCmp);
 
 b("File \"bs_poly_mutable_set_test.res\", line 16, characters 4-11", Belt_MutableSet.removeCheck(u, 0));
 
@@ -65,7 +63,7 @@ for(let i = 0 ,i_finish = r.length; i < i_finish; ++i){
   Belt_MutableSet.remove(u, r[i]);
 }
 
-b("File \"bs_poly_mutable_set_test.res\", line 28, characters 4-11", u.data === undefined);
+b("File \"bs_poly_mutable_set_test.res\", line 28, characters 4-11", Belt_MutableSet.isEmpty(u));
 
 Belt_MutableSet.add(u, 0);
 
@@ -77,13 +75,13 @@ Belt_MutableSet.add(u, 0);
 
 eq("File \"bs_poly_mutable_set_test.res\", line 33, characters 5-12", Belt_internalAVLset.size(u.data), 3);
 
-b("File \"bs_poly_mutable_set_test.res\", line 34, characters 4-11", u.data !== undefined);
+b("File \"bs_poly_mutable_set_test.res\", line 34, characters 4-11", !Belt_MutableSet.isEmpty(u));
 
 for(let i$1 = 0; i$1 <= 3; ++i$1){
   Belt_MutableSet.remove(u, i$1);
 }
 
-b("File \"bs_poly_mutable_set_test.res\", line 38, characters 4-11", u.data === undefined);
+b("File \"bs_poly_mutable_set_test.res\", line 38, characters 4-11", Belt_MutableSet.isEmpty(u));
 
 Belt_MutableSet.mergeMany(u, Array_data_util.randomRange(0, 20000));
 
@@ -115,11 +113,9 @@ b("File \"bs_poly_mutable_set_test.res\", line 52, characters 4-11", Belt_Mutabl
 
 Belt_MutableSet.removeMany(u, Array_data_util.randomRange(10000, 30000));
 
-b("File \"bs_poly_mutable_set_test.res\", line 54, characters 4-11", u.data === undefined);
-
-let none$1 = Array_data_util.randomRange(1000, 2000);
+b("File \"bs_poly_mutable_set_test.res\", line 54, characters 4-11", Belt_MutableSet.isEmpty(u));
 
-let v = Belt_MutableSet.fromArray(none$1, IntCmp);
+let v = Belt_MutableSet.fromArray(Array_data_util.randomRange(1000, 2000), IntCmp);
 
 let bs = Belt_Array.map(Array_data_util.randomRange(500, 1499), (function (x) {
   return Belt_MutableSet.removeCheck(v, x);
@@ -153,12 +149,10 @@ eq("File \"bs_poly_mutable_set_test.res\", line 77, characters 5-12", indeedAded
 
 eq("File \"bs_poly_mutable_set_test.res\", line 78, characters 5-12", Belt_internalAVLset.size(v.data), 1501);
 
-let d = {
+b("File \"bs_poly_mutable_set_test.res\", line 79, characters 4-11", Belt_MutableSet.isEmpty({
   cmp: IntCmp.cmp,
   data: undefined
-};
-
-b("File \"bs_poly_mutable_set_test.res\", line 79, characters 4-11", d.data === undefined);
+}));
 
 eq("File \"bs_poly_mutable_set_test.res\", line 80, characters 5-12", Belt_internalAVLset.minimum(v.data), 500);
 
@@ -208,9 +202,7 @@ b("File \"bs_poly_mutable_set_test.res\", line 94, characters 4-11", Belt_Mutabl
 
 b("File \"bs_poly_mutable_set_test.res\", line 95, characters 4-11", Belt_MutableSet.subset(bb, v));
 
-let d$1 = Belt_MutableSet.intersect(aa, bb);
-
-b("File \"bs_poly_mutable_set_test.res\", line 96, characters 4-11", d$1.data === undefined);
+b("File \"bs_poly_mutable_set_test.res\", line 96, characters 4-11", Belt_MutableSet.isEmpty(Belt_MutableSet.intersect(aa, bb)));
 
 let c = Belt_MutableSet.removeCheck(v, 1000);
 
@@ -238,52 +230,28 @@ b("File \"bs_poly_mutable_set_test.res\", line 103, characters 4-11", Belt_Mutab
 
 b("File \"bs_poly_mutable_set_test.res\", line 104, characters 4-11", Belt_MutableSet.subset(bb$1, v));
 
-let d$2 = Belt_MutableSet.intersect(aa$1, bb$1);
-
-b("File \"bs_poly_mutable_set_test.res\", line 105, characters 4-11", d$2.data === undefined);
-
-let none$2 = Array_data_util.randomRange(0, 100);
+b("File \"bs_poly_mutable_set_test.res\", line 105, characters 4-11", Belt_MutableSet.isEmpty(Belt_MutableSet.intersect(aa$1, bb$1)));
 
-let aa$2 = Belt_MutableSet.fromArray(none$2, IntCmp);
+let aa$2 = Belt_MutableSet.fromArray(Array_data_util.randomRange(0, 100), IntCmp);
 
-let none$3 = Array_data_util.randomRange(40, 120);
-
-let bb$2 = Belt_MutableSet.fromArray(none$3, IntCmp);
+let bb$2 = Belt_MutableSet.fromArray(Array_data_util.randomRange(40, 120), IntCmp);
 
 let cc = Belt_MutableSet.union(aa$2, bb$2);
 
-let none$4 = Array_data_util.randomRange(0, 120);
-
-b("File \"bs_poly_mutable_set_test.res\", line 115, characters 4-11", Belt_MutableSet.eq(cc, Belt_MutableSet.fromArray(none$4, IntCmp)));
-
-let none$5 = Array_data_util.randomRange(0, 20);
-
-let none$6 = Array_data_util.randomRange(21, 40);
+b("File \"bs_poly_mutable_set_test.res\", line 115, characters 4-11", Belt_MutableSet.eq(cc, Belt_MutableSet.fromArray(Array_data_util.randomRange(0, 120), IntCmp)));
 
-let none$7 = Array_data_util.randomRange(0, 40);
-
-b("File \"bs_poly_mutable_set_test.res\", line 118, characters 4-11", Belt_MutableSet.eq(Belt_MutableSet.union(Belt_MutableSet.fromArray(none$5, IntCmp), Belt_MutableSet.fromArray(none$6, IntCmp)), Belt_MutableSet.fromArray(none$7, IntCmp)));
+b("File \"bs_poly_mutable_set_test.res\", line 118, characters 4-11", Belt_MutableSet.eq(Belt_MutableSet.union(Belt_MutableSet.fromArray(Array_data_util.randomRange(0, 20), IntCmp), Belt_MutableSet.fromArray(Array_data_util.randomRange(21, 40), IntCmp)), Belt_MutableSet.fromArray(Array_data_util.randomRange(0, 40), IntCmp)));
 
 let dd = Belt_MutableSet.intersect(aa$2, bb$2);
 
-let none$8 = Array_data_util.randomRange(40, 100);
-
-b("File \"bs_poly_mutable_set_test.res\", line 122, characters 4-11", Belt_MutableSet.eq(dd, Belt_MutableSet.fromArray(none$8, IntCmp)));
-
-let none$9 = Array_data_util.randomRange(0, 20);
+b("File \"bs_poly_mutable_set_test.res\", line 122, characters 4-11", Belt_MutableSet.eq(dd, Belt_MutableSet.fromArray(Array_data_util.randomRange(40, 100), IntCmp)));
 
-let none$10 = Array_data_util.randomRange(21, 40);
-
-b("File \"bs_poly_mutable_set_test.res\", line 124, characters 4-11", Belt_MutableSet.eq(Belt_MutableSet.intersect(Belt_MutableSet.fromArray(none$9, IntCmp), Belt_MutableSet.fromArray(none$10, IntCmp)), {
+b("File \"bs_poly_mutable_set_test.res\", line 124, characters 4-11", Belt_MutableSet.eq(Belt_MutableSet.intersect(Belt_MutableSet.fromArray(Array_data_util.randomRange(0, 20), IntCmp), Belt_MutableSet.fromArray(Array_data_util.randomRange(21, 40), IntCmp)), {
   cmp: IntCmp.cmp,
   data: undefined
 }));
 
-let none$11 = Array_data_util.randomRange(21, 40);
-
-let none$12 = Array_data_util.randomRange(0, 20);
-
-b("File \"bs_poly_mutable_set_test.res\", line 128, characters 4-11", Belt_MutableSet.eq(Belt_MutableSet.intersect(Belt_MutableSet.fromArray(none$11, IntCmp), Belt_MutableSet.fromArray(none$12, IntCmp)), {
+b("File \"bs_poly_mutable_set_test.res\", line 128, characters 4-11", Belt_MutableSet.eq(Belt_MutableSet.intersect(Belt_MutableSet.fromArray(Array_data_util.randomRange(21, 40), IntCmp), Belt_MutableSet.fromArray(Array_data_util.randomRange(0, 20), IntCmp)), {
   cmp: IntCmp.cmp,
   data: undefined
 }));
@@ -307,41 +275,17 @@ b("File \"bs_poly_mutable_set_test.res\", line 131, characters 4-11", Belt_Mutab
   5
 ], IntCmp)));
 
-let none$13 = Array_data_util.randomRange(0, 39);
-
-b("File \"bs_poly_mutable_set_test.res\", line 132, characters 4-11", Belt_MutableSet.eq(Belt_MutableSet.diff(aa$2, bb$2), Belt_MutableSet.fromArray(none$13, IntCmp)));
-
-let none$14 = Array_data_util.randomRange(101, 120);
-
-b("File \"bs_poly_mutable_set_test.res\", line 133, characters 4-11", Belt_MutableSet.eq(Belt_MutableSet.diff(bb$2, aa$2), Belt_MutableSet.fromArray(none$14, IntCmp)));
-
-let none$15 = Array_data_util.randomRange(21, 40);
-
-let none$16 = Array_data_util.randomRange(0, 20);
-
-let none$17 = Array_data_util.randomRange(21, 40);
-
-b("File \"bs_poly_mutable_set_test.res\", line 135, characters 4-11", Belt_MutableSet.eq(Belt_MutableSet.diff(Belt_MutableSet.fromArray(none$15, IntCmp), Belt_MutableSet.fromArray(none$16, IntCmp)), Belt_MutableSet.fromArray(none$17, IntCmp)));
-
-let none$18 = Array_data_util.randomRange(0, 20);
-
-let none$19 = Array_data_util.randomRange(21, 40);
-
-let none$20 = Array_data_util.randomRange(0, 20);
-
-b("File \"bs_poly_mutable_set_test.res\", line 142, characters 4-11", Belt_MutableSet.eq(Belt_MutableSet.diff(Belt_MutableSet.fromArray(none$18, IntCmp), Belt_MutableSet.fromArray(none$19, IntCmp)), Belt_MutableSet.fromArray(none$20, IntCmp)));
-
-let none$21 = Array_data_util.randomRange(0, 20);
+b("File \"bs_poly_mutable_set_test.res\", line 132, characters 4-11", Belt_MutableSet.eq(Belt_MutableSet.diff(aa$2, bb$2), Belt_MutableSet.fromArray(Array_data_util.randomRange(0, 39), IntCmp)));
 
-let none$22 = Array_data_util.randomRange(0, 40);
+b("File \"bs_poly_mutable_set_test.res\", line 133, characters 4-11", Belt_MutableSet.eq(Belt_MutableSet.diff(bb$2, aa$2), Belt_MutableSet.fromArray(Array_data_util.randomRange(101, 120), IntCmp)));
 
-let none$23 = Array_data_util.randomRange(0, -1);
+b("File \"bs_poly_mutable_set_test.res\", line 135, characters 4-11", Belt_MutableSet.eq(Belt_MutableSet.diff(Belt_MutableSet.fromArray(Array_data_util.randomRange(21, 40), IntCmp), Belt_MutableSet.fromArray(Array_data_util.randomRange(0, 20), IntCmp)), Belt_MutableSet.fromArray(Array_data_util.randomRange(21, 40), IntCmp)));
 
-b("File \"bs_poly_mutable_set_test.res\", line 150, characters 4-11", Belt_MutableSet.eq(Belt_MutableSet.diff(Belt_MutableSet.fromArray(none$21, IntCmp), Belt_MutableSet.fromArray(none$22, IntCmp)), Belt_MutableSet.fromArray(none$23, IntCmp)));
+b("File \"bs_poly_mutable_set_test.res\", line 142, characters 4-11", Belt_MutableSet.eq(Belt_MutableSet.diff(Belt_MutableSet.fromArray(Array_data_util.randomRange(0, 20), IntCmp), Belt_MutableSet.fromArray(Array_data_util.randomRange(21, 40), IntCmp)), Belt_MutableSet.fromArray(Array_data_util.randomRange(0, 20), IntCmp)));
 
-let none$24 = Array_data_util.randomRange(0, 1000);
+b("File \"bs_poly_mutable_set_test.res\", line 150, characters 4-11", Belt_MutableSet.eq(Belt_MutableSet.diff(Belt_MutableSet.fromArray(Array_data_util.randomRange(0, 20), IntCmp), Belt_MutableSet.fromArray(Array_data_util.randomRange(0, 40), IntCmp)), Belt_MutableSet.fromArray(Array_data_util.randomRange(0, -1), IntCmp)));
 
-let a0 = Belt_MutableSet.fromArray(none$24, IntCmp);
+let a0 = Belt_MutableSet.fromArray(Array_data_util.randomRange(0, 1000), IntCmp);
 
 let a1 = Belt_MutableSet.keep(a0, (function (x) {
   return x % 2 === 0;
diff --git a/jscomp/test/bs_queue_test.js b/jscomp/test/bs_queue_test.js
index 432d8a9bdb..a57ca4a829 100644
--- a/jscomp/test/bs_queue_test.js
+++ b/jscomp/test/bs_queue_test.js
@@ -56,7 +56,7 @@ if (!(Caml_obj.equal(Belt_MutableQueue.toArray(q), []) && q.length === 0)) {
       });
 }
 
-if (!(Caml_obj.equal(Belt_MutableQueue.toArray($plus$plus(q, 1)), [1]) && q.length === 1)) {
+if (!(Caml_obj.equal(Belt_MutableQueue.toArray((Belt_MutableQueue.add(q, 1), q)), [1]) && q.length === 1)) {
   throw new Error("Assert_failure", {
         cause: {
           RE_EXN_ID: "Assert_failure",
@@ -69,7 +69,7 @@ if (!(Caml_obj.equal(Belt_MutableQueue.toArray($plus$plus(q, 1)), [1]) && q.leng
       });
 }
 
-if (!(Caml_obj.equal(Belt_MutableQueue.toArray($plus$plus(q, 2)), [
+if (!(Caml_obj.equal(Belt_MutableQueue.toArray((Belt_MutableQueue.add(q, 2), q)), [
     1,
     2
   ]) && q.length === 2)) {
@@ -85,7 +85,7 @@ if (!(Caml_obj.equal(Belt_MutableQueue.toArray($plus$plus(q, 2)), [
       });
 }
 
-if (!(Caml_obj.equal(Belt_MutableQueue.toArray($plus$plus(q, 3)), [
+if (!(Caml_obj.equal(Belt_MutableQueue.toArray((Belt_MutableQueue.add(q, 3), q)), [
     1,
     2,
     3
@@ -102,7 +102,7 @@ if (!(Caml_obj.equal(Belt_MutableQueue.toArray($plus$plus(q, 3)), [
       });
 }
 
-if (!(Caml_obj.equal(Belt_MutableQueue.toArray($plus$plus(q, 4)), [
+if (!(Caml_obj.equal(Belt_MutableQueue.toArray((Belt_MutableQueue.add(q, 4), q)), [
     1,
     2,
     3,
@@ -250,7 +250,7 @@ let q$1 = {
   last: undefined
 };
 
-if (Belt_MutableQueue.popExn($plus$plus(q$1, 1)) !== 1) {
+if (Belt_MutableQueue.popExn((Belt_MutableQueue.add(q$1, 1), q$1)) !== 1) {
   throw new Error("Assert_failure", {
         cause: {
           RE_EXN_ID: "Assert_failure",
@@ -276,7 +276,7 @@ if (!does_raise(Belt_MutableQueue.popExn, q$1)) {
       });
 }
 
-if (Belt_MutableQueue.popExn($plus$plus(q$1, 2)) !== 2) {
+if (Belt_MutableQueue.popExn((Belt_MutableQueue.add(q$1, 2), q$1)) !== 2) {
   throw new Error("Assert_failure", {
         cause: {
           RE_EXN_ID: "Assert_failure",
@@ -321,7 +321,7 @@ let q$2 = {
   last: undefined
 };
 
-if (Belt_MutableQueue.peekExn($plus$plus(q$2, 1)) !== 1) {
+if (Belt_MutableQueue.peekExn((Belt_MutableQueue.add(q$2, 1), q$2)) !== 1) {
   throw new Error("Assert_failure", {
         cause: {
           RE_EXN_ID: "Assert_failure",
@@ -334,7 +334,7 @@ if (Belt_MutableQueue.peekExn($plus$plus(q$2, 1)) !== 1) {
       });
 }
 
-if (Belt_MutableQueue.peekExn($plus$plus(q$2, 2)) !== 1) {
+if (Belt_MutableQueue.peekExn((Belt_MutableQueue.add(q$2, 2), q$2)) !== 1) {
   throw new Error("Assert_failure", {
         cause: {
           RE_EXN_ID: "Assert_failure",
@@ -347,7 +347,7 @@ if (Belt_MutableQueue.peekExn($plus$plus(q$2, 2)) !== 1) {
       });
 }
 
-if (Belt_MutableQueue.peekExn($plus$plus(q$2, 3)) !== 1) {
+if (Belt_MutableQueue.peekExn((Belt_MutableQueue.add(q$2, 3), q$2)) !== 1) {
   throw new Error("Assert_failure", {
         cause: {
           RE_EXN_ID: "Assert_failure",
@@ -1371,4 +1371,4 @@ exports.b = b;
 exports.Q = Q;
 exports.does_raise = does_raise;
 exports.$plus$plus = $plus$plus;
-/* q Not a pure module */
+/*  Not a pure module */
diff --git a/jscomp/test/bs_set_int_test.js b/jscomp/test/bs_set_int_test.js
index 83bfef16e5..80039fd7d5 100644
--- a/jscomp/test/bs_set_int_test.js
+++ b/jscomp/test/bs_set_int_test.js
@@ -52,7 +52,7 @@ let u = Belt_SetInt.intersect(Belt_SetInt.fromArray([
   5
 ]));
 
-b("File \"bs_set_int_test.res\", line 27, characters 11-18", $eq$tilde(u, [3]));
+b("File \"bs_set_int_test.res\", line 27, characters 11-18", Belt_SetInt.eq(Belt_SetInt.fromArray([3]), u));
 
 function range(i, j) {
   return $$Array.init((j - i | 0) + 1 | 0, (function (k) {
@@ -68,7 +68,9 @@ function revRange(i, j) {
 
 let v = Belt_SetInt.fromArray($$Array.append(range(100, 1000), revRange(400, 1500)));
 
-b("File \"bs_set_int_test.res\", line 37, characters 4-11", $eq$tilde(v, range(100, 1500)));
+let i = range(100, 1500);
+
+b("File \"bs_set_int_test.res\", line 37, characters 4-11", Belt_SetInt.eq(Belt_SetInt.fromArray(i), v));
 
 let match = Belt_SetInt.partition(v, (function (x) {
   return x % 3 === 0;
@@ -78,11 +80,11 @@ let l;
 
 let r;
 
-for(let i = 100; i <= 1500; ++i){
-  if (i % 3 === 0) {
-    l = Belt_SetInt.add(l, i);
+for(let i$1 = 100; i$1 <= 1500; ++i$1){
+  if (i$1 % 3 === 0) {
+    l = Belt_SetInt.add(l, i$1);
   } else {
-    r = Belt_SetInt.add(r, i);
+    r = Belt_SetInt.add(r, i$1);
   }
 }
 
@@ -94,17 +96,41 @@ b("File \"bs_set_int_test.res\", line 50, characters 4-11", Belt_SetInt.eq(match
 
 b("File \"bs_set_int_test.res\", line 51, characters 4-11", Belt_SetInt.eq(match[1], nr));
 
-b("File \"bs_set_int_test.res\", line 55, characters 2-9", $eq$tilde(Belt_SetInt.intersect(Belt_SetInt.fromArray(range(1, 100)), Belt_SetInt.fromArray(range(50, 200))), range(50, 100)));
+let i$2 = range(50, 100);
+
+let s = Belt_SetInt.intersect(Belt_SetInt.fromArray(range(1, 100)), Belt_SetInt.fromArray(range(50, 200)));
+
+b("File \"bs_set_int_test.res\", line 55, characters 2-9", Belt_SetInt.eq(Belt_SetInt.fromArray(i$2), s));
+
+let i$3 = range(1, 200);
+
+let s$1 = Belt_SetInt.union(Belt_SetInt.fromArray(range(1, 100)), Belt_SetInt.fromArray(range(50, 200)));
+
+b("File \"bs_set_int_test.res\", line 66, characters 2-9", Belt_SetInt.eq(Belt_SetInt.fromArray(i$3), s$1));
+
+let i$4 = range(1, 49);
+
+let s$2 = Belt_SetInt.diff(Belt_SetInt.fromArray(range(1, 100)), Belt_SetInt.fromArray(range(50, 200)));
+
+b("File \"bs_set_int_test.res\", line 77, characters 2-9", Belt_SetInt.eq(Belt_SetInt.fromArray(i$4), s$2));
+
+let i$5 = revRange(50, 100);
+
+let s$3 = Belt_SetInt.intersect(Belt_SetInt.fromArray(revRange(1, 100)), Belt_SetInt.fromArray(revRange(50, 200)));
+
+b("File \"bs_set_int_test.res\", line 88, characters 2-9", Belt_SetInt.eq(Belt_SetInt.fromArray(i$5), s$3));
+
+let i$6 = revRange(1, 200);
 
-b("File \"bs_set_int_test.res\", line 66, characters 2-9", $eq$tilde(Belt_SetInt.union(Belt_SetInt.fromArray(range(1, 100)), Belt_SetInt.fromArray(range(50, 200))), range(1, 200)));
+let s$4 = Belt_SetInt.union(Belt_SetInt.fromArray(revRange(1, 100)), Belt_SetInt.fromArray(revRange(50, 200)));
 
-b("File \"bs_set_int_test.res\", line 77, characters 2-9", $eq$tilde(Belt_SetInt.diff(Belt_SetInt.fromArray(range(1, 100)), Belt_SetInt.fromArray(range(50, 200))), range(1, 49)));
+b("File \"bs_set_int_test.res\", line 99, characters 2-9", Belt_SetInt.eq(Belt_SetInt.fromArray(i$6), s$4));
 
-b("File \"bs_set_int_test.res\", line 88, characters 2-9", $eq$tilde(Belt_SetInt.intersect(Belt_SetInt.fromArray(revRange(1, 100)), Belt_SetInt.fromArray(revRange(50, 200))), revRange(50, 100)));
+let i$7 = revRange(1, 49);
 
-b("File \"bs_set_int_test.res\", line 99, characters 2-9", $eq$tilde(Belt_SetInt.union(Belt_SetInt.fromArray(revRange(1, 100)), Belt_SetInt.fromArray(revRange(50, 200))), revRange(1, 200)));
+let s$5 = Belt_SetInt.diff(Belt_SetInt.fromArray(revRange(1, 100)), Belt_SetInt.fromArray(revRange(50, 200)));
 
-b("File \"bs_set_int_test.res\", line 110, characters 2-9", $eq$tilde(Belt_SetInt.diff(Belt_SetInt.fromArray(revRange(1, 100)), Belt_SetInt.fromArray(revRange(50, 200))), revRange(1, 49)));
+b("File \"bs_set_int_test.res\", line 110, characters 2-9", Belt_SetInt.eq(Belt_SetInt.fromArray(i$7), s$5));
 
 let ss = [
   1,
diff --git a/jscomp/test/bs_unwrap_test.js b/jscomp/test/bs_unwrap_test.js
index 25e7a582d8..9280a5b7ba 100644
--- a/jscomp/test/bs_unwrap_test.js
+++ b/jscomp/test/bs_unwrap_test.js
@@ -48,9 +48,7 @@ console.log(5, Caml_option.option_unwrap(some_arg));
 
 console.log(6, undefined);
 
-console.log(7, Caml_option.option_unwrap((function () {
-  console.log("trace");
-})()));
+console.log(7, Caml_option.option_unwrap((console.log("trace"), undefined)));
 
 function dyn_log3(prim0, prim1, prim2) {
   console.log(prim0.VAL, Caml_option.option_unwrap(prim1));
diff --git a/jscomp/test/caml_format_test.js b/jscomp/test/caml_format_test.js
index 6fee11065f..f184d33bb2 100644
--- a/jscomp/test/caml_format_test.js
+++ b/jscomp/test/caml_format_test.js
@@ -423,7 +423,7 @@ let of_string_data = [
   ]
 ];
 
-let extra = Pervasives.$at(suites, Pervasives.$at($$Array.to_list($$Array.mapi((function (i, param) {
+Mt.from_pair_suites("Caml_format_test", Pervasives.$at(suites, Pervasives.$at($$Array.to_list($$Array.mapi((function (i, param) {
   let str_result = param[2];
   let f = param[1];
   let fmt = param[0];
@@ -450,9 +450,7 @@ let extra = Pervasives.$at(suites, Pervasives.$at($$Array.to_list($$Array.mapi((
       };
     })
   ];
-}), of_string_data)))));
-
-Mt.from_pair_suites("Caml_format_test", extra);
+}), of_string_data))))));
 
 let float_suites = {
   hd: "float_nan",
diff --git a/jscomp/test/coercion_module_alias_test.js b/jscomp/test/coercion_module_alias_test.js
index 42b9423056..996ebb34db 100644
--- a/jscomp/test/coercion_module_alias_test.js
+++ b/jscomp/test/coercion_module_alias_test.js
@@ -24,9 +24,7 @@ let prim$2 = Char.chr(66);
 
 console.log(prim$2);
 
-function f(x) {
-  return List.length(x);
-}
+let f = List.length;
 
 function g(x) {
   return List.length(List.map((function (prim) {
diff --git a/jscomp/test/complex_if_test.js b/jscomp/test/complex_if_test.js
index 6fc7e2d7c5..ac9d60a393 100644
--- a/jscomp/test/complex_if_test.js
+++ b/jscomp/test/complex_if_test.js
@@ -127,7 +127,7 @@ let suites_0 = [
   (function (param) {
     return {
       TAG: "Eq",
-      _0: string_escaped("\x00\x01\x02\x03\x04\x05\x06\x07\b\t\n\x0b\x0c\r\x0e\x0f\x10\x11\x12\x13\x14\x15\x16\x17\x18\x19\x1a\x1b\x1c\x1d\x1e\x1f !\"#$%&'()*+,-./0123456789:;<=>?@ABCDEFGHIJKLMNOPQRSTUVWXYZ[\\]^_`abcdefghijklmnopqrstuvwxyz{|}~\x7f\x80\x81\x82\x83\x84\x85\x86\x87\x88\x89\x8a\x8b\x8c\x8d\x8e\x8f\x90\x91\x92\x93\x94\x95\x96\x97\x98\x99\x9a\x9b\x9c\x9d\x9e\x9f\xa0\xa1\xa2\xa3\xa4\xa5\xa6\xa7\xa8\xa9\xaa\xab\xac\xad\xae\xaf\xb0\xb1\xb2\xb3\xb4\xb5\xb6\xb7\xb8\xb9\xba\xbb\xbc\xbd\xbe\xbf\xc0\xc1\xc2\xc3\xc4\xc5\xc6\xc7\xc8\xc9\xca\xcb\xcc\xcd\xce\xcf\xd0\xd1\xd2\xd3\xd4\xd5\xd6\xd7\xd8\xd9\xda\xdb\xdc\xdd\xde\xdf\xe0\xe1\xe2\xe3\xe4\xe5\xe6\xe7\xe8\xe9\xea\xeb\xec\xed\xee\xef\xf0\xf1\xf2\xf3\xf4\xf5\xf6\xf7\xf8\xf9\xfa\xfb\xfc\xfd\xfe\xff"),
+      _0: Bytes.to_string(escaped(Bytes.of_string("\x00\x01\x02\x03\x04\x05\x06\x07\b\t\n\x0b\x0c\r\x0e\x0f\x10\x11\x12\x13\x14\x15\x16\x17\x18\x19\x1a\x1b\x1c\x1d\x1e\x1f !\"#$%&'()*+,-./0123456789:;<=>?@ABCDEFGHIJKLMNOPQRSTUVWXYZ[\\]^_`abcdefghijklmnopqrstuvwxyz{|}~\x7f\x80\x81\x82\x83\x84\x85\x86\x87\x88\x89\x8a\x8b\x8c\x8d\x8e\x8f\x90\x91\x92\x93\x94\x95\x96\x97\x98\x99\x9a\x9b\x9c\x9d\x9e\x9f\xa0\xa1\xa2\xa3\xa4\xa5\xa6\xa7\xa8\xa9\xaa\xab\xac\xad\xae\xaf\xb0\xb1\xb2\xb3\xb4\xb5\xb6\xb7\xb8\xb9\xba\xbb\xbc\xbd\xbe\xbf\xc0\xc1\xc2\xc3\xc4\xc5\xc6\xc7\xc8\xc9\xca\xcb\xcc\xcd\xce\xcf\xd0\xd1\xd2\xd3\xd4\xd5\xd6\xd7\xd8\xd9\xda\xdb\xdc\xdd\xde\xdf\xe0\xe1\xe2\xe3\xe4\xe5\xe6\xe7\xe8\xe9\xea\xeb\xec\xed\xee\xef\xf0\xf1\xf2\xf3\xf4\xf5\xf6\xf7\xf8\xf9\xfa\xfb\xfc\xfd\xfe\xff"))),
       _1: "\\000\\001\\002\\003\\004\\005\\006\\007\\b\\t\\n\\011\\012\\r\\014\\015\\016\\017\\018\\019\\020\\021\\022\\023\\024\\025\\026\\027\\028\\029\\030\\031 !\\\"#$%&'()*+,-./0123456789:;<=>?@ABCDEFGHIJKLMNOPQRSTUVWXYZ[\\\\]^_`abcdefghijklmnopqrstuvwxyz{|}~\\127\\128\\129\\130\\131\\132\\133\\134\\135\\136\\137\\138\\139\\140\\141\\142\\143\\144\\145\\146\\147\\148\\149\\150\\151\\152\\153\\154\\155\\156\\157\\158\\159\\160\\161\\162\\163\\164\\165\\166\\167\\168\\169\\170\\171\\172\\173\\174\\175\\176\\177\\178\\179\\180\\181\\182\\183\\184\\185\\186\\187\\188\\189\\190\\191\\192\\193\\194\\195\\196\\197\\198\\199\\200\\201\\202\\203\\204\\205\\206\\207\\208\\209\\210\\211\\212\\213\\214\\215\\216\\217\\218\\219\\220\\221\\222\\223\\224\\225\\226\\227\\228\\229\\230\\231\\232\\233\\234\\235\\236\\237\\238\\239\\240\\241\\242\\243\\244\\245\\246\\247\\248\\249\\250\\251\\252\\253\\254\\255"
     };
   })
diff --git a/jscomp/test/digest_test.js b/jscomp/test/digest_test.js
index 645a59a61f..f6f053b4cc 100644
--- a/jscomp/test/digest_test.js
+++ b/jscomp/test/digest_test.js
@@ -145,7 +145,7 @@ let ref = [
   "b325dc1c6f5e7a2b7cf465b9feab7948"
 ];
 
-let extra = Pervasives.$at({
+Mt.from_pair_suites("Digest_test", Pervasives.$at({
   hd: [
     "File \"digest_test.res\", line 9, characters 9-16",
     (function () {
@@ -228,9 +228,7 @@ let extra = Pervasives.$at({
       };
     })
   ];
-}), Ext_array_test.range(0, 129))));
-
-Mt.from_pair_suites("Digest_test", extra);
+}), Ext_array_test.range(0, 129)))));
 
 exports.f = f;
-/* extra Not a pure module */
+/*  Not a pure module */
diff --git a/jscomp/test/event_ffi.js b/jscomp/test/event_ffi.js
index c1a9fb070f..d4144f53a3 100644
--- a/jscomp/test/event_ffi.js
+++ b/jscomp/test/event_ffi.js
@@ -34,8 +34,7 @@ function h34(x) {
 }
 
 function ocaml_run(b, c) {
-  let x = 1;
-  return (x + b | 0) + c | 0;
+  return (1 + b | 0) + c | 0;
 }
 
 function a0() {
diff --git a/jscomp/test/ext_array_test.js b/jscomp/test/ext_array_test.js
index 6e74676a71..de2c274cb2 100644
--- a/jscomp/test/ext_array_test.js
+++ b/jscomp/test/ext_array_test.js
@@ -104,32 +104,32 @@ function filter_map(f, a) {
 }
 
 function range(from, to_) {
-  if (from <= to_) {
-    return $$Array.init((to_ - from | 0) + 1 | 0, (function (i) {
-      return i + from | 0;
-    }));
+  if (from > to_) {
+    throw new Error("Invalid_argument", {
+          cause: {
+            RE_EXN_ID: "Invalid_argument",
+            _1: "Ext_array_test.range"
+          }
+        });
   }
-  throw new Error("Invalid_argument", {
-        cause: {
-          RE_EXN_ID: "Invalid_argument",
-          _1: "Ext_array_test.range"
-        }
-      });
+  return $$Array.init((to_ - from | 0) + 1 | 0, (function (i) {
+    return i + from | 0;
+  }));
 }
 
 function map2i(f, a, b) {
   let len = a.length;
-  if (len === b.length) {
-    return $$Array.mapi((function (i, a) {
-      return f(i, a, b[i]);
-    }), a);
+  if (len !== b.length) {
+    throw new Error("Invalid_argument", {
+          cause: {
+            RE_EXN_ID: "Invalid_argument",
+            _1: "Ext_array_test.map2i"
+          }
+        });
   }
-  throw new Error("Invalid_argument", {
-        cause: {
-          RE_EXN_ID: "Invalid_argument",
-          _1: "Ext_array_test.map2i"
-        }
-      });
+  return $$Array.mapi((function (i, a) {
+    return f(i, a, b[i]);
+  }), a);
 }
 
 function tolist_aux(a, f, _i, _res) {
diff --git a/jscomp/test/ext_bytes_test.js b/jscomp/test/ext_bytes_test.js
index 9c496d4a89..6e333d5bf1 100644
--- a/jscomp/test/ext_bytes_test.js
+++ b/jscomp/test/ext_bytes_test.js
@@ -5,7 +5,6 @@ let Mt = require("./mt.js");
 let Caml = require("../../lib/js/caml.js");
 let Char = require("../../lib/js/char.js");
 let Bytes = require("../../lib/js/bytes.js");
-let $$String = require("../../lib/js/string.js");
 let Caml_bytes = require("../../lib/js/caml_bytes.js");
 let Caml_exceptions = require("../../lib/js/caml_exceptions.js");
 let Caml_js_exceptions = require("../../lib/js/caml_js_exceptions.js");
@@ -158,25 +157,21 @@ function starts_with(xs, prefix, p) {
   }
 }
 
-let a = Bytes.init(100, (function (i) {
-  return Char.chr(i);
-}));
+let a = Bytes.init(100, Char.chr);
 
 Bytes.blit(a, 5, a, 10, 10);
 
 eq("File \"ext_bytes_test.res\", line 116, characters 4-11", a, Bytes.of_string("\x00\x01\x02\x03\x04\x05\x06\x07\b\t\x05\x06\x07\b\t\n\x0b\x0c\r\x0e\x14\x15\x16\x17\x18\x19\x1a\x1b\x1c\x1d\x1e\x1f !\"#$%&'()*+,-./0123456789:;<=>?@ABCDEFGHIJKLMNOPQRSTUVWXYZ[\\]^_`abc"));
 
-let a$1 = Bytes.init(100, (function (i) {
-  return Char.chr(i);
-}));
+let a$1 = Bytes.init(100, Char.chr);
 
 Bytes.blit(a$1, 10, a$1, 5, 10);
 
 eq("File \"ext_bytes_test.res\", line 128, characters 4-11", a$1, Bytes.of_string("\x00\x01\x02\x03\x04\n\x0b\x0c\r\x0e\x0f\x10\x11\x12\x13\x0f\x10\x11\x12\x13\x14\x15\x16\x17\x18\x19\x1a\x1b\x1c\x1d\x1e\x1f !\"#$%&'()*+,-./0123456789:;<=>?@ABCDEFGHIJKLMNOPQRSTUVWXYZ[\\]^_`abc"));
 
-let a$2 = $$String.init(100, (function (i) {
-  return Char.chr(i);
-}));
+let f = Char.chr;
+
+let a$2 = Bytes.unsafe_to_string(Bytes.init(100, f));
 
 let b = Bytes.init(100, (function (i) {
   return /* '\000' */0;
@@ -196,7 +191,7 @@ let s2 = Bytes.of_string(s1);
 
 eq("File \"ext_bytes_test.res\", line 153, characters 5-12", s, s2);
 
-function f(a, b) {
+function f$1(a, b) {
   return [
     Caml_bytes.bytes_greaterthan(a, b),
     Caml_bytes.bytes_greaterequal(a, b),
@@ -223,6 +218,6 @@ exports.test_id = test_id;
 exports.eq = eq;
 exports.escaped = escaped;
 exports.starts_with = starts_with;
-exports.f = f;
+exports.f = f$1;
 exports.f_0 = f_0;
 /* a Not a pure module */
diff --git a/jscomp/test/ext_filename_test.js b/jscomp/test/ext_filename_test.js
index af53b2859e..b4df9c0f72 100644
--- a/jscomp/test/ext_filename_test.js
+++ b/jscomp/test/ext_filename_test.js
@@ -2,9 +2,9 @@
 'use strict';
 
 let Sys = require("../../lib/js/sys.js");
-let Lazy = require("../../lib/js/lazy.js");
 let List = require("../../lib/js/list.js");
-let $$String = require("../../lib/js/string.js");
+let $$Array = require("../../lib/js/array.js");
+let Bytes = require("../../lib/js/bytes.js");
 let Caml_sys = require("../../lib/js/caml_sys.js");
 let Filename = require("../../lib/js/filename.js");
 let Pervasives = require("../../lib/js/pervasives.js");
@@ -19,7 +19,7 @@ let node_parent = "..";
 
 let node_current = ".";
 
-let cwd = Lazy.from_fun(function () {
+let cwd = CamlinternalLazy.from_fun(function () {
   return Caml_sys.sys_getcwd();
 });
 
@@ -63,10 +63,11 @@ function chop_extension(locOpt, name) {
   catch (raw_exn){
     let exn = Caml_js_exceptions.internalToOCamlException(raw_exn);
     if (exn.RE_EXN_ID === "Invalid_argument") {
+      let s = "Filename.chop_extension ( " + loc + " : " + name + " )";
       throw new Error("Invalid_argument", {
             cause: {
               RE_EXN_ID: "Invalid_argument",
-              _1: "Filename.chop_extension ( " + loc + " : " + name + " )"
+              _1: s
             }
           });
     }
@@ -114,13 +115,13 @@ function relative_path(file_or_dir_1, file_or_dir_2) {
   };
   let ys = go(dir1, dir2);
   if (ys && ys.hd === node_parent) {
-    return $$String.concat(node_sep, ys);
+    return $$Array.of_list(ys).join(node_sep);
   }
-  let __x = {
+  let xs = {
     hd: node_current,
     tl: ys
   };
-  return $$String.concat(node_sep, __x);
+  return $$Array.of_list(xs).join(node_sep);
 }
 
 function node_relative_path(node_modules_shorten, file1, dep_file) {
@@ -146,10 +147,11 @@ function node_relative_path(node_modules_shorten, file1, dep_file) {
     while(true) {
       let i = _i;
       if (i >= len) {
+        let s = "invalid path: " + file2;
         throw new Error("Failure", {
               cause: {
                 RE_EXN_ID: "Failure",
-                _1: "invalid path: " + file2
+                _1: s
               }
             });
       }
@@ -175,10 +177,11 @@ function find_root_filename(_cwd, filename) {
       _cwd = cwd$p;
       continue;
     }
+    let s = filename + " not found from " + cwd;
     throw new Error("Failure", {
           cause: {
             RE_EXN_ID: "Failure",
-            _1: filename + " not found from " + cwd
+            _1: s
           }
         });
   };
@@ -188,17 +191,19 @@ function find_package_json_dir(cwd) {
   return find_root_filename(cwd, Test_literals.bsconfig_json);
 }
 
-let package_dir = Lazy.from_fun(function () {
+let package_dir = CamlinternalLazy.from_fun(function () {
   let cwd$1 = CamlinternalLazy.force(cwd);
   return find_root_filename(cwd$1, Test_literals.bsconfig_json);
 });
 
 function module_name_of_file(file) {
-  return $$String.capitalize_ascii(Filename.chop_extension(Filename.basename(file)));
+  let s = Filename.chop_extension(Filename.basename(file));
+  return Bytes.unsafe_to_string(Bytes.capitalize_ascii(Bytes.unsafe_of_string(s)));
 }
 
 function module_name_of_file_if_any(file) {
-  return $$String.capitalize_ascii(chop_extension_if_any(Filename.basename(file)));
+  let s = chop_extension_if_any(Filename.basename(file));
+  return Bytes.unsafe_to_string(Bytes.capitalize_ascii(Bytes.unsafe_of_string(s)));
 }
 
 function combine(p1, p2) {
@@ -254,9 +259,7 @@ function rel_normalized_absolute_path(from, to_) {
     let xss = _xss;
     if (!xss) {
       if (yss) {
-        return List.fold_left((function (acc, x) {
-          return Filename.concat(acc, x);
-        }), yss.hd, yss.tl);
+        return List.fold_left(Filename.concat, yss.hd, yss.tl);
       } else {
         return Ext_string_test.empty;
       }
@@ -275,9 +278,7 @@ function rel_normalized_absolute_path(from, to_) {
     let start = List.fold_left((function (acc, param) {
       return Filename.concat(acc, Ext_string_test.parent_dir_lit);
     }), Ext_string_test.parent_dir_lit, xs);
-    return List.fold_left((function (acc, v) {
-      return Filename.concat(acc, v);
-    }), start, yss);
+    return List.fold_left(Filename.concat, start, yss);
   };
 }
 
@@ -354,10 +355,11 @@ if (Sys.unix) {
 } else if (Sys.win32 || false) {
   simple_convert_node_path_to_os_path = Ext_string_test.replace_slash_backward;
 } else {
+  let s = "Unknown OS : " + Sys.os_type;
   throw new Error("Failure", {
         cause: {
           RE_EXN_ID: "Failure",
-          _1: "Unknown OS : " + Sys.os_type
+          _1: s
         }
       });
 }
@@ -387,4 +389,4 @@ exports.rel_normalized_absolute_path = rel_normalized_absolute_path;
 exports.normalize_absolute_path = normalize_absolute_path;
 exports.get_extension = get_extension;
 exports.simple_convert_node_path_to_os_path = simple_convert_node_path_to_os_path;
-/* cwd Not a pure module */
+/* simple_convert_node_path_to_os_path Not a pure module */
diff --git a/jscomp/test/ext_list_test.js b/jscomp/test/ext_list_test.js
index d2870ed0bd..f502e1c310 100644
--- a/jscomp/test/ext_list_test.js
+++ b/jscomp/test/ext_list_test.js
@@ -303,15 +303,15 @@ function flat_map2(f, lx, ly) {
             }
           });
     }
-    if (!ly$1) {
-      return List.rev(acc);
+    if (ly$1) {
+      throw new Error("Invalid_argument", {
+            cause: {
+              RE_EXN_ID: "Invalid_argument",
+              _1: "Ext_list_test.flat_map2"
+            }
+          });
     }
-    throw new Error("Invalid_argument", {
-          cause: {
-            RE_EXN_ID: "Invalid_argument",
-            _1: "Ext_list_test.flat_map2"
-          }
-        });
+    return List.rev(acc);
   };
 }
 
@@ -431,15 +431,15 @@ function fold_right2_last(f, l1, l2, accu) {
           }
         });
   }
-  if (!l2) {
-    return accu;
+  if (l2) {
+    throw new Error("Invalid_argument", {
+          cause: {
+            RE_EXN_ID: "Invalid_argument",
+            _1: "List.fold_right2"
+          }
+        });
   }
-  throw new Error("Invalid_argument", {
-        cause: {
-          RE_EXN_ID: "Invalid_argument",
-          _1: "List.fold_right2"
-        }
-      });
+  return accu;
 }
 
 function init(n, f) {
@@ -449,18 +449,18 @@ function init(n, f) {
 function take(n, l) {
   let arr = $$Array.of_list(l);
   let arr_length = arr.length;
-  if (arr_length >= n) {
-    return [
-      $$Array.to_list($$Array.sub(arr, 0, n)),
-      $$Array.to_list($$Array.sub(arr, n, arr_length - n | 0))
-    ];
+  if (arr_length < n) {
+    throw new Error("Invalid_argument", {
+          cause: {
+            RE_EXN_ID: "Invalid_argument",
+            _1: "Ext_list_test.take"
+          }
+        });
   }
-  throw new Error("Invalid_argument", {
-        cause: {
-          RE_EXN_ID: "Invalid_argument",
-          _1: "Ext_list_test.take"
-        }
-      });
+  return [
+    $$Array.to_list($$Array.sub(arr, 0, n)),
+    $$Array.to_list($$Array.sub(arr, n, arr_length - n | 0))
+  ];
 }
 
 function try_take(n, l) {
diff --git a/jscomp/test/ext_string_test.js b/jscomp/test/ext_string_test.js
index 53b4cc582a..9939699352 100644
--- a/jscomp/test/ext_string_test.js
+++ b/jscomp/test/ext_string_test.js
@@ -216,15 +216,15 @@ function unsafe_for_all_range(s, _start, finish, p) {
 
 function for_all_range(s, start, finish, p) {
   let len = s.length;
-  if (!(start < 0 || finish >= len)) {
-    return unsafe_for_all_range(s, start, finish, p);
+  if (start < 0 || finish >= len) {
+    throw new Error("Invalid_argument", {
+          cause: {
+            RE_EXN_ID: "Invalid_argument",
+            _1: "Ext_string_test.for_all_range"
+          }
+        });
   }
-  throw new Error("Invalid_argument", {
-        cause: {
-          RE_EXN_ID: "Invalid_argument",
-          _1: "Ext_string_test.for_all_range"
-        }
-      });
+  return unsafe_for_all_range(s, start, finish, p);
 }
 
 function for_all(p, s) {
@@ -300,27 +300,27 @@ function contain_substring(s, sub) {
 
 function non_overlap_count(sub, s) {
   let sub_len = sub.length;
-  if (sub.length !== 0) {
-    let _acc = 0;
-    let _off = 0;
-    while(true) {
-      let off = _off;
-      let acc = _acc;
-      let i = find(off, sub, s);
-      if (i < 0) {
-        return acc;
-      }
-      _off = i + sub_len | 0;
-      _acc = acc + 1 | 0;
-      continue;
-    };
+  if (sub.length === 0) {
+    throw new Error("Invalid_argument", {
+          cause: {
+            RE_EXN_ID: "Invalid_argument",
+            _1: "Ext_string_test.non_overlap_count"
+          }
+        });
   }
-  throw new Error("Invalid_argument", {
-        cause: {
-          RE_EXN_ID: "Invalid_argument",
-          _1: "Ext_string_test.non_overlap_count"
-        }
-      });
+  let _acc = 0;
+  let _off = 0;
+  while(true) {
+    let off = _off;
+    let acc = _acc;
+    let i = find(off, sub, s);
+    if (i < 0) {
+      return acc;
+    }
+    _off = i + sub_len | 0;
+    _acc = acc + 1 | 0;
+    continue;
+  };
 }
 
 function rfind(sub, s) {
@@ -553,15 +553,15 @@ function unsafe_no_char_idx(x, ch, _i, last_idx) {
 
 function no_char(x, ch, i, len) {
   let str_len = x.length;
-  if (!(i < 0 || i >= str_len || len >= str_len)) {
-    return unsafe_no_char(x, ch, i, len);
+  if (i < 0 || i >= str_len || len >= str_len) {
+    throw new Error("Invalid_argument", {
+          cause: {
+            RE_EXN_ID: "Invalid_argument",
+            _1: "Ext_string_test.no_char"
+          }
+        });
   }
-  throw new Error("Invalid_argument", {
-        cause: {
-          RE_EXN_ID: "Invalid_argument",
-          _1: "Ext_string_test.no_char"
-        }
-      });
+  return unsafe_no_char(x, ch, i, len);
 }
 
 function no_slash(x) {
diff --git a/jscomp/test/ffi_arity_test.js b/jscomp/test/ffi_arity_test.js
index 71cf9a5704..eb3eb30760 100644
--- a/jscomp/test/ffi_arity_test.js
+++ b/jscomp/test/ffi_arity_test.js
@@ -63,9 +63,7 @@ function abc(x, y, z) {
   return (x + y | 0) + z | 0;
 }
 
-function abc_u(x, y, z) {
-  return abc(x, y, z);
-}
+let abc_u = abc;
 
 fff();
 
diff --git a/jscomp/test/float_test.js b/jscomp/test/float_test.js
index 9968b2483c..7998fe9d09 100644
--- a/jscomp/test/float_test.js
+++ b/jscomp/test/float_test.js
@@ -322,7 +322,7 @@ let b = match$4[1];
 
 let a = match$4[0];
 
-let extra = Pervasives.$at({
+Mt.from_pair_suites("Float_test", Pervasives.$at({
   hd: [
     "mod_float",
     (function () {
@@ -370,9 +370,7 @@ let extra = Pervasives.$at({
       }
     }
   }
-}, Pervasives.$at(from_pairs(results), suites.contents));
-
-Mt.from_pair_suites("Float_test", extra);
+}, Pervasives.$at(from_pairs(results), suites.contents)));
 
 exports.test_id = test_id;
 exports.suites = suites;
diff --git a/jscomp/test/for_loop_test.js b/jscomp/test/for_loop_test.js
index 03b984a4c1..167938029a 100644
--- a/jscomp/test/for_loop_test.js
+++ b/jscomp/test/for_loop_test.js
@@ -164,9 +164,6 @@ function for_9() {
       tl: v.contents
     };
   };
-  let get = function () {
-    return $$Array.of_list(List.rev(v.contents));
-  };
   let vv = {
     contents: 0
   };
@@ -203,7 +200,7 @@ function for_9() {
   }), arr2);
   return [[
       vv.contents,
-      get(),
+      $$Array.of_list(List.rev(v.contents)),
       vv2.contents
     ]];
 }
diff --git a/jscomp/test/format_test.js b/jscomp/test/format_test.js
index 9c7de3c192..e7dbc96ed5 100644
--- a/jscomp/test/format_test.js
+++ b/jscomp/test/format_test.js
@@ -3,7 +3,7 @@
 
 let Mt = require("./mt.js");
 let List = require("../../lib/js/list.js");
-let $$String = require("../../lib/js/string.js");
+let Bytes = require("../../lib/js/bytes.js");
 let Pervasives = require("../../lib/js/pervasives.js");
 let Caml_format = require("../../lib/js/caml_format.js");
 
@@ -174,7 +174,9 @@ let literals = {
 
 aux_list("File \"format_test.res\", line 72, characters 18-25", literals);
 
-eq("File \"format_test.res\", line 74, characters 12-19", $$String.uppercase_ascii(Caml_format.hexstring_of_float(7.875, -1, /* '-' */45)), "0X1.F8P+2");
+let s = Caml_format.hexstring_of_float(7.875, -1, /* '-' */45);
+
+eq("File \"format_test.res\", line 74, characters 12-19", Bytes.unsafe_to_string(Bytes.uppercase_ascii(Bytes.unsafe_of_string(s))), "0X1.F8P+2");
 
 function scan_float(loc, s, expect) {
   eq(loc, Caml_format.float_of_string(s), expect);
diff --git a/jscomp/test/functors.js b/jscomp/test/functors.js
index 7af4f0d308..f56f95b996 100644
--- a/jscomp/test/functors.js
+++ b/jscomp/test/functors.js
@@ -20,7 +20,7 @@ function F(X, Y) {
     return Y.foo(X.foo(x));
   };
   let sheep = function (x) {
-    return 1 + cow(x) | 0;
+    return 1 + Y.foo(X.foo(x)) | 0;
   };
   return {
     cow: cow,
@@ -29,11 +29,8 @@ function F(X, Y) {
 }
 
 function F1(X, Y) {
-  let cow = function (x) {
-    return Y.foo(X.foo(x));
-  };
   let sheep = function (x) {
-    return 1 + cow(x) | 0;
+    return 1 + Y.foo(X.foo(x)) | 0;
   };
   return {
     sheep: sheep
@@ -41,11 +38,8 @@ function F1(X, Y) {
 }
 
 function F2(X, Y) {
-  let cow = function (x) {
-    return Y.foo(X.foo(x));
-  };
   let sheep = function (x) {
-    return 1 + cow(x) | 0;
+    return 1 + Y.foo(X.foo(x)) | 0;
   };
   return {
     sheep: sheep
@@ -54,11 +48,8 @@ function F2(X, Y) {
 
 let M = {
   F: (function (funarg, funarg$1) {
-    let cow = function (x) {
-      return funarg$1.foo(funarg.foo(x));
-    };
     let sheep = function (x) {
-      return 1 + cow(x) | 0;
+      return 1 + funarg$1.foo(funarg.foo(x)) | 0;
     };
     return {
       sheep: sheep
diff --git a/jscomp/test/gpr_1154_test.js b/jscomp/test/gpr_1154_test.js
index 96e585681a..b951f6fc97 100644
--- a/jscomp/test/gpr_1154_test.js
+++ b/jscomp/test/gpr_1154_test.js
@@ -52,7 +52,7 @@ function g2(x) {
   return Caml_int64.or_(x, (v.contents = v.contents + 1 | 0, x));
 }
 
-let a = g2(Int64.one);
+let a = Caml_int64.or_(Int64.one, (v.contents = v.contents + 1 | 0, Int64.one));
 
 eq("File \"gpr_1154_test.res\", line 28, characters 12-19", v.contents, 1);
 
diff --git a/jscomp/test/gpr_1423_app_test.js b/jscomp/test/gpr_1423_app_test.js
index fee9718e51..da8edcbc0e 100644
--- a/jscomp/test/gpr_1423_app_test.js
+++ b/jscomp/test/gpr_1423_app_test.js
@@ -40,9 +40,7 @@ function foo2(f) {
   return f("a1", undefined);
 }
 
-eq("File \"gpr_1423_app_test.res\", line 15, characters 12-19", (function (none, extra) {
-  return none + "a2";
-})("a1", undefined), "a1a2");
+eq("File \"gpr_1423_app_test.res\", line 15, characters 12-19", "a1a2", "a1a2");
 
 Mt.from_pair_suites("Gpr_1423_app_test", suites.contents);
 
diff --git a/jscomp/test/gpr_1667_test.js b/jscomp/test/gpr_1667_test.js
index 75efb35a82..a1f9c44493 100644
--- a/jscomp/test/gpr_1667_test.js
+++ b/jscomp/test/gpr_1667_test.js
@@ -28,10 +28,6 @@ function eq(loc, x, y) {
   };
 }
 
-(function (z) {
-  return 0;
-})(false) === 0;
-
 eq("File \"gpr_1667_test.res\", line 24, characters 5-12", 0, 0);
 
 Mt.from_pair_suites("Gpr_1667_test", suites.contents);
diff --git a/jscomp/test/gpr_1692_test.js b/jscomp/test/gpr_1692_test.js
index ba792ec3b4..884c49a7dc 100644
--- a/jscomp/test/gpr_1692_test.js
+++ b/jscomp/test/gpr_1692_test.js
@@ -2,10 +2,8 @@
 'use strict';
 
 
-(function (x) {
-  return function (f) {
+((function (f) {
     return 0;
-  };
-})("")("");
+  })(""));
 
 /*  Not a pure module */
diff --git a/jscomp/test/gpr_3697_test.js b/jscomp/test/gpr_3697_test.js
index 1d38845ec9..884b7b1a50 100644
--- a/jscomp/test/gpr_3697_test.js
+++ b/jscomp/test/gpr_3697_test.js
@@ -1,13 +1,14 @@
 // Generated by ReScript, PLEASE EDIT WITH CARE
 'use strict';
 
-let Lazy = require("../../lib/js/lazy.js");
 let CamlinternalLazy = require("../../lib/js/camlinternalLazy.js");
 
 function fix() {
   return {
     TAG: "Fix",
-    _0: Lazy.from_fun(fix)
+    _0: CamlinternalLazy.from_fun(function () {
+      return fix();
+    })
   };
 }
 
diff --git a/jscomp/test/gpr_3875_test.js b/jscomp/test/gpr_3875_test.js
index abb933adc3..51d9d0db8d 100644
--- a/jscomp/test/gpr_3875_test.js
+++ b/jscomp/test/gpr_3875_test.js
@@ -17,32 +17,33 @@ let Xx = {
 
 function compilerBug(a, b, c, f) {
   let exit = 0;
-  let exit$1 = 0;
-  if (a === "x") {
+  if (a !== "x") {
     exit = 2;
-  } else {
-    exit$1 = 3;
-  }
-  if (exit$1 === 3) {
-    exit = b === "x" ? 2 : 1;
   }
-  switch (exit) {
-    case 1 :
-        if (c) {
-          result.contents = "No x, c is true";
-        } else {
-          result.contents = "No x, c is false";
-        }
-        return;
-    case 2 :
-        if (f()) {
-          result.contents = "Some x, f returns true";
-        } else {
-          result.contents = "Some x, f returns false";
-        }
-        return;
+  if (exit === 2) {
+    if (b === undefined) {
+      if (c) {
+        result.contents = "No x, c is true";
+      } else {
+        result.contents = "No x, c is false";
+      }
+      return;
+    }
+    if (b !== "x") {
+      if (c) {
+        result.contents = "No x, c is true";
+      } else {
+        result.contents = "No x, c is false";
+      }
+      return;
+    }
     
   }
+  if (f()) {
+    result.contents = "Some x, f returns true";
+  } else {
+    result.contents = "Some x, f returns false";
+  }
 }
 
 let suites = {
diff --git a/jscomp/test/gpr_405_test.js b/jscomp/test/gpr_405_test.js
index a27fad4498..de96727ae0 100644
--- a/jscomp/test/gpr_405_test.js
+++ b/jscomp/test/gpr_405_test.js
@@ -125,4 +125,4 @@ function Make(funarg) {
 }
 
 exports.Make = Make;
-/* Hashtbl Not a pure module */
+/* No side effect */
diff --git a/jscomp/test/gpr_4265_test.js b/jscomp/test/gpr_4265_test.js
index f40f38c687..56b6ad3757 100644
--- a/jscomp/test/gpr_4265_test.js
+++ b/jscomp/test/gpr_4265_test.js
@@ -3,6 +3,7 @@
 
 let Mt = require("./mt.js");
 let Belt_MutableMapInt = require("../../lib/js/belt_MutableMapInt.js");
+let Belt_internalMapInt = require("../../lib/js/belt_internalMapInt.js");
 
 let suites = {
   contents: /* [] */0
@@ -37,7 +38,7 @@ add(486);
 
 Belt_MutableMapInt.remove(mockMap, 1726);
 
-let n1 = Belt_MutableMapInt.getExn(mockMap, 6667);
+let n1 = Belt_internalMapInt.getExn(mockMap.data, 6667);
 
 eq("File \"gpr_4265_test.res\", line 18, characters 3-10", n, n1);
 
@@ -51,4 +52,4 @@ exports.add = add;
 exports.remove = remove;
 exports.n = n;
 exports.n1 = n1;
-/* mockMap Not a pure module */
+/*  Not a pure module */
diff --git a/jscomp/test/hashtbl_test.js b/jscomp/test/hashtbl_test.js
index c64c09f5b9..979cf206eb 100644
--- a/jscomp/test/hashtbl_test.js
+++ b/jscomp/test/hashtbl_test.js
@@ -39,10 +39,9 @@ function g(count) {
     Hashtbl.replace(tbl, (i$1 << 1), String(i$1));
   }
   let v = to_list(tbl);
-  let v$1 = List.sort((function (param, param$1) {
+  return $$Array.of_list(List.sort((function (param, param$1) {
     return Caml.int_compare(param[0], param$1[0]);
-  }), v);
-  return $$Array.of_list(v$1);
+  }), v));
 }
 
 let suites_0 = [
diff --git a/jscomp/test/inline_string_test.js b/jscomp/test/inline_string_test.js
index 09713e1294..c81d1e60ac 100644
--- a/jscomp/test/inline_string_test.js
+++ b/jscomp/test/inline_string_test.js
@@ -22,19 +22,7 @@ console.log([
 
 console.log([
   "A",
-  (function (x) {
-    switch (x.TAG) {
-      case "A" :
-          return "A";
-      case "B" :
-          return "B";
-      default:
-        return "?";
-    }
-  })({
-    TAG: "A",
-    _0: 3
-  })
+  "A"
 ]);
 
 /*  Not a pure module */
diff --git a/jscomp/test/int64_mul_div_test.js b/jscomp/test/int64_mul_div_test.js
index 6935d118e7..0b3755be19 100644
--- a/jscomp/test/int64_mul_div_test.js
+++ b/jscomp/test/int64_mul_div_test.js
@@ -1600,7 +1600,7 @@ function from_to_string(xs) {
   }), $$Array.to_list(xs));
 }
 
-let extra = Pervasives.$at(from_pairs("random", pairs), Pervasives.$at(from_pairs("small", small_pairs), Pervasives.$at(List.mapi((function (i, param) {
+Mt.from_pair_suites("Int64_mul_div_test", Pervasives.$at(from_pairs("random", pairs), Pervasives.$at(from_pairs("small", small_pairs), Pervasives.$at(List.mapi((function (i, param) {
   let f = param[1];
   let i64 = param[0];
   return [
@@ -1676,9 +1676,7 @@ let extra = Pervasives.$at(from_pairs("random", pairs), Pervasives.$at(from_pair
       tl: /* [] */0
     }
   }
-})))))));
-
-Mt.from_pair_suites("Int64_mul_div_test", extra);
+}))))))));
 
 exports.commutative_mul = commutative_mul;
 exports.pairs = pairs;
@@ -1693,4 +1691,4 @@ exports.to_string = to_string;
 exports.int64_compare_tests = int64_compare_tests;
 exports.from_compare = from_compare;
 exports.from_to_string = from_to_string;
-/* extra Not a pure module */
+/*  Not a pure module */
diff --git a/jscomp/test/int_hashtbl_test.js b/jscomp/test/int_hashtbl_test.js
index d6c1d924b2..bf32e0b592 100644
--- a/jscomp/test/int_hashtbl_test.js
+++ b/jscomp/test/int_hashtbl_test.js
@@ -42,15 +42,12 @@ function g(H, count) {
       tl: acc
     };
   }), tbl, /* [] */0);
-  let v$1 = List.sort((function (param, param$1) {
+  return $$Array.of_list(List.sort((function (param, param$1) {
     return Caml.int_compare(param[0], param$1[0]);
-  }), v);
-  return $$Array.of_list(v$1);
+  }), v));
 }
 
-function hash(x) {
-  return Hashtbl.hash(x);
-}
+let hash = Hashtbl.hash;
 
 function equal(x, y) {
   return x === y;
diff --git a/jscomp/test/js_json_test.js b/jscomp/test/js_json_test.js
index e9533d4cbb..92bd902fb2 100644
--- a/jscomp/test/js_json_test.js
+++ b/jscomp/test/js_json_test.js
@@ -82,34 +82,21 @@ add_test("File \"js_json_test.res\", line 22, characters 11-18", (function () {
     };
   }
   let ty2 = Js_json.classify(v$1);
-  if (typeof ty2 !== "object" || ty2.TAG !== "JSONArray") {
+  if (typeof ty2 !== "object") {
     return {
       TAG: "Ok",
       _0: false
     };
-  } else {
-    return (function () {
-      return {
-        TAG: "Ok",
-        _0: true
-      };
-    })((ty2._0.forEach(function (x) {
-      let ty3 = Js_json.classify(x);
-      if (typeof ty3 !== "object") {
-        throw new Error("Assert_failure", {
-              cause: {
-                RE_EXN_ID: "Assert_failure",
-                _1: [
-                  "js_json_test.res",
-                  37,
-                  19
-                ]
-              }
-            });
-      }
-      if (ty3.TAG === "JSONNumber") {
-        return;
-      }
+  }
+  if (ty2.TAG !== "JSONArray") {
+    return {
+      TAG: "Ok",
+      _0: false
+    };
+  }
+  ty2._0.forEach(function (x) {
+    let ty3 = Js_json.classify(x);
+    if (typeof ty3 !== "object") {
       throw new Error("Assert_failure", {
             cause: {
               RE_EXN_ID: "Assert_failure",
@@ -120,8 +107,25 @@ add_test("File \"js_json_test.res\", line 22, characters 11-18", (function () {
               ]
             }
           });
-    }), undefined));
-  }
+    }
+    if (ty3.TAG === "JSONNumber") {
+      return;
+    }
+    throw new Error("Assert_failure", {
+          cause: {
+            RE_EXN_ID: "Assert_failure",
+            _1: [
+              "js_json_test.res",
+              37,
+              19
+            ]
+          }
+        });
+  });
+  return {
+    TAG: "Ok",
+    _0: true
+  };
 }));
 
 eq("File \"js_json_test.res\", line 48, characters 5-12", Js_json.test(v, "Object"), true);
@@ -740,7 +744,7 @@ function id(obj) {
 }
 
 function idtest(obj) {
-  eq("File \"js_json_test.res\", line 355, characters 23-30", obj, id(obj));
+  eq("File \"js_json_test.res\", line 355, characters 23-30", obj, Js_json.deserializeUnsafe(Js_json.serializeExn(obj)));
 }
 
 idtest(undefined);
diff --git a/jscomp/test/lazy_demo.js b/jscomp/test/lazy_demo.js
index d950f3be7d..1d4fa28466 100644
--- a/jscomp/test/lazy_demo.js
+++ b/jscomp/test/lazy_demo.js
@@ -1,15 +1,14 @@
 // Generated by ReScript, PLEASE EDIT WITH CARE
 'use strict';
 
-let Lazy = require("../../lib/js/lazy.js");
 let CamlinternalLazy = require("../../lib/js/camlinternalLazy.js");
 
-let lazy1 = Lazy.from_fun(function () {
+let lazy1 = CamlinternalLazy.from_fun(function () {
   console.log("Hello, lazy");
   return 1;
 });
 
-let lazy2 = Lazy.from_fun(function () {
+let lazy2 = CamlinternalLazy.from_fun(function () {
   return 3;
 });
 
@@ -25,4 +24,4 @@ exports.lazy1 = lazy1;
 exports.lazy2 = lazy2;
 exports.la = la;
 exports.lb = lb;
-/* lazy1 Not a pure module */
+/*  Not a pure module */
diff --git a/jscomp/test/lazy_test.js b/jscomp/test/lazy_test.js
index b8e3f1dc4e..217632df99 100644
--- a/jscomp/test/lazy_test.js
+++ b/jscomp/test/lazy_test.js
@@ -9,7 +9,7 @@ let u = {
   contents: 3
 };
 
-let v = Lazy.from_fun(function () {
+let v = CamlinternalLazy.from_fun(function () {
   u.contents = 32;
 });
 
@@ -27,7 +27,7 @@ let u_v = {
   contents: 0
 };
 
-let u$1 = Lazy.from_fun(function () {
+let u$1 = CamlinternalLazy.from_fun(function () {
   u_v.contents = 2;
 });
 
@@ -35,27 +35,31 @@ CamlinternalLazy.force(u$1);
 
 let exotic = CamlinternalLazy.force;
 
-let l_from_fun = Lazy.from_fun(function () {
+let l_from_fun = CamlinternalLazy.from_fun(function () {
   return 3;
 });
 
-let forward_test = Lazy.from_fun(function () {
+function f() {
   let u = 3;
   u = u + 1 | 0;
   return u;
+}
+
+let forward_test = CamlinternalLazy.from_fun(function () {
+  return f();
 });
 
-let f005 = Lazy.from_fun(function () {
+let f005 = CamlinternalLazy.from_fun(function () {
   return 6;
 });
 
-let f006 = Lazy.from_fun(function () {
+let f006 = CamlinternalLazy.from_fun(function () {
   return function () {
     return 3;
   };
 });
 
-let f007 = Lazy.from_fun(function () {
+let f007 = CamlinternalLazy.from_fun(function () {
   throw new Error("Not_found", {
         cause: {
           RE_EXN_ID: "Not_found"
@@ -63,18 +67,20 @@ let f007 = Lazy.from_fun(function () {
       });
 });
 
-let f008 = Lazy.from_fun(function () {
+function f$1() {
   console.log("hi");
   throw new Error("Not_found", {
         cause: {
           RE_EXN_ID: "Not_found"
         }
       });
+}
+
+let f008 = CamlinternalLazy.from_fun(function () {
+  return f$1();
 });
 
-function a2(x) {
-  return CamlinternalLazy.from_val(x);
-}
+let a2 = CamlinternalLazy.from_val;
 
 let a3 = CamlinternalLazy.from_val(3);
 
@@ -139,12 +145,11 @@ Mt.from_pair_suites("Lazy_test", {
           hd: [
             "lazy_from_val2",
             (function () {
-              let v = Lazy.from_fun(function () {
-                return 3;
-              });
               return {
                 TAG: "Eq",
-                _0: CamlinternalLazy.force(CamlinternalLazy.force(CamlinternalLazy.from_val(v))),
+                _0: CamlinternalLazy.force(CamlinternalLazy.force(CamlinternalLazy.from_val(CamlinternalLazy.from_fun(function () {
+                  return 3;
+                })))),
                 _1: 3
               };
             })
@@ -210,7 +215,7 @@ Mt.from_pair_suites("Lazy_test", {
                         (function () {
                           return {
                             TAG: "Ok",
-                            _0: !Lazy.is_val(Lazy.from_fun(function () {
+                            _0: !Lazy.is_val(CamlinternalLazy.from_fun(function () {
                               throw new Error("Not_found", {
                                     cause: {
                                       RE_EXN_ID: "Not_found"
@@ -251,4 +256,4 @@ exports.a5 = a5;
 exports.a6 = a6;
 exports.a7 = a7;
 exports.a8 = a8;
-/* v Not a pure module */
+/*  Not a pure module */
diff --git a/jscomp/test/map_find_test.js b/jscomp/test/map_find_test.js
index 10193d80f0..31ef48ae2c 100644
--- a/jscomp/test/map_find_test.js
+++ b/jscomp/test/map_find_test.js
@@ -367,36 +367,30 @@ let s = List.fold_left((function (acc, param) {
   }
 });
 
-let extra_0 = [
-  "int",
-  (function () {
-    return {
-      TAG: "Eq",
-      _0: find(10, m),
-      _1: /* 'a' */97
-    };
-  })
-];
-
-let extra_1 = {
+Mt.from_pair_suites("Map_find_test", {
   hd: [
-    "string",
+    "int",
     (function () {
       return {
         TAG: "Eq",
-        _0: find$1("10", s),
+        _0: find(10, m),
         _1: /* 'a' */97
       };
     })
   ],
-  tl: /* [] */0
-};
-
-let extra = {
-  hd: extra_0,
-  tl: extra_1
-};
-
-Mt.from_pair_suites("Map_find_test", extra);
+  tl: {
+    hd: [
+      "string",
+      (function () {
+        return {
+          TAG: "Eq",
+          _0: find$1("10", s),
+          _1: /* 'a' */97
+        };
+      })
+    ],
+    tl: /* [] */0
+  }
+});
 
 /* m Not a pure module */
diff --git a/jscomp/test/mario_game.js b/jscomp/test/mario_game.js
index e9159f4930..635e2e3132 100644
--- a/jscomp/test/mario_game.js
+++ b/jscomp/test/mario_game.js
@@ -702,7 +702,11 @@ function make_type$1(typ, ctx) {
   switch (typ) {
     case "BrickChunkL" :
     case "BrickChunkR" :
-        break;
+        return {
+          sprite: make_particle$1(typ, ctx),
+          rot: 0,
+          lifetime: 300
+        };
     default:
       return {
         sprite: make_particle$1(typ, ctx),
@@ -710,11 +714,6 @@ function make_type$1(typ, ctx) {
         lifetime: 30
       };
   }
-  return {
-    sprite: make_particle$1(typ, ctx),
-    rot: 0,
-    lifetime: 300
-  };
 }
 
 function make$1(velOpt, accOpt, part_type, pos, ctx) {
@@ -1652,10 +1651,9 @@ function process_collision(dir, c1, c2, state) {
   let o1$2;
   let t2$1;
   let o2$2;
-  let o1$3;
   switch (c1.TAG) {
     case "Player" :
-        let o1$4 = c1._2;
+        let o1$3 = c1._2;
         let s1$2 = c1._1;
         switch (c2.TAG) {
           case "Player" :
@@ -1669,14 +1667,14 @@ function process_collision(dir, c1, c2, state) {
               let typ$1 = c2._0;
               if (dir === "South") {
                 s1 = s1$2;
-                o1 = o1$4;
+                o1 = o1$3;
                 typ = typ$1;
                 s2 = s2$2;
                 o2 = o2$3;
                 exit = 1;
               } else {
                 s1$1 = s1$2;
-                o1$1 = o1$4;
+                o1$1 = o1$3;
                 t2 = typ$1;
                 s2$1 = s2$2;
                 o2$1 = o2$3;
@@ -1684,7 +1682,7 @@ function process_collision(dir, c1, c2, state) {
               }
               break;
           case "Item" :
-              o1$2 = o1$4;
+              o1$2 = o1$3;
               t2$1 = c2._0;
               o2$2 = c2._2;
               exit = 3;
@@ -1697,14 +1695,14 @@ function process_collision(dir, c1, c2, state) {
                   switch (t) {
                     case "Brick" :
                         if (c1._0 === "BigM") {
-                          collide_block(undefined, dir, o1$4);
+                          collide_block(undefined, dir, o1$3);
                           dec_health(o2$4);
                           return [
                             undefined,
                             undefined
                           ];
                         } else {
-                          collide_block(undefined, dir, o1$4);
+                          collide_block(undefined, dir, o1$3);
                           return [
                             undefined,
                             undefined
@@ -1717,7 +1715,7 @@ function process_collision(dir, c1, c2, state) {
                           undefined
                         ];
                     default:
-                      collide_block(undefined, dir, o1$4);
+                      collide_block(undefined, dir, o1$3);
                       return [
                         undefined,
                         undefined
@@ -1725,8 +1723,8 @@ function process_collision(dir, c1, c2, state) {
                   }
                 } else {
                   let updated_block = evolve_block(o2$4, context);
-                  let spawned_item = spawn_above(o1$4.dir, o2$4, t._0, context);
-                  collide_block(undefined, dir, o1$4);
+                  let spawned_item = spawn_above(o1$3.dir, o2$4, t._0, context);
+                  collide_block(undefined, dir, o1$3);
                   return [
                     spawned_item,
                     updated_block
@@ -1742,20 +1740,20 @@ function process_collision(dir, c1, c2, state) {
                       undefined
                     ];
                   }
-                  exit$1 = 5;
+                  exit$1 = 4;
                 } else {
-                  exit$1 = 5;
+                  exit$1 = 4;
                 }
-                if (exit$1 === 5) {
+                if (exit$1 === 4) {
                   if (dir === "South") {
                     state.multiplier = 1;
-                    collide_block(undefined, dir, o1$4);
+                    collide_block(undefined, dir, o1$3);
                     return [
                       undefined,
                       undefined
                     ];
                   }
-                  collide_block(undefined, dir, o1$4);
+                  collide_block(undefined, dir, o1$3);
                   return [
                     undefined,
                     undefined
@@ -1768,26 +1766,26 @@ function process_collision(dir, c1, c2, state) {
         }
         break;
     case "Enemy" :
-        let o1$5 = c1._2;
+        let o1$4 = c1._2;
         let s1$3 = c1._1;
         let t1 = c1._0;
         switch (c2.TAG) {
           case "Player" :
-              let o1$6 = c2._2;
+              let o1$5 = c2._2;
               let s1$4 = c2._1;
               if (dir === "North") {
                 s1 = s1$4;
-                o1 = o1$6;
+                o1 = o1$5;
                 typ = t1;
                 s2 = s1$3;
-                o2 = o1$5;
+                o2 = o1$4;
                 exit = 1;
               } else {
                 s1$1 = s1$4;
-                o1$1 = o1$6;
+                o1$1 = o1$5;
                 t2 = t1;
                 s2$1 = s1$3;
-                o2$1 = o1$5;
+                o2$1 = o1$4;
                 exit = 2;
               }
               break;
@@ -1839,7 +1837,7 @@ function process_collision(dir, c1, c2, state) {
                         
                       }
                       if (exit$3 === 4) {
-                        rev_dir(o1$5, t1, s1$3);
+                        rev_dir(o1$4, t1, s1$3);
                         rev_dir(o2$5, t2$2, s2$3);
                         return [
                           undefined,
@@ -1851,14 +1849,14 @@ function process_collision(dir, c1, c2, state) {
               }
               switch (exit$2) {
                 case 1 :
-                    dec_health(o1$5);
+                    dec_health(o1$4);
                     dec_health(o2$5);
                     return [
                       undefined,
                       undefined
                     ];
                 case 2 :
-                    if (o1$5.vel.x === 0) {
+                    if (o1$4.vel.x === 0) {
                       rev_dir(o2$5, t2$2, s2$3);
                       return [
                         undefined,
@@ -1873,13 +1871,13 @@ function process_collision(dir, c1, c2, state) {
                     }
                 case 3 :
                     if (o2$5.vel.x === 0) {
-                      rev_dir(o1$5, t1, s1$3);
+                      rev_dir(o1$4, t1, s1$3);
                       return [
                         undefined,
                         undefined
                       ];
                     } else {
-                      dec_health(o1$5);
+                      dec_health(o1$4);
                       return [
                         undefined,
                         undefined
@@ -1899,56 +1897,67 @@ function process_collision(dir, c1, c2, state) {
               switch (dir) {
                 case "North" :
                 case "South" :
-                    o1$3 = o1$5;
-                    exit = 4;
-                    break;
+                    collide_block(undefined, dir, o1$4);
+                    return [
+                      undefined,
+                      undefined
+                    ];
                 case "East" :
                 case "West" :
-                    exit$4 = 5;
+                    exit$4 = 4;
                     break;
                 
               }
-              if (exit$4 === 5) {
+              if (exit$4 === 4) {
                 let exit$5 = 0;
                 let typ$2;
                 switch (t1) {
                   case "GKoopaShell" :
                       if (typeof t2$3 !== "object") {
-                        exit$5 = t2$3 === "Brick" ? 7 : 6;
+                        if (t2$3 === "Brick") {
+                          dec_health(o2$6);
+                          reverse_left_right(o1$4);
+                          return [
+                            undefined,
+                            undefined
+                          ];
+                        }
+                        exit$5 = 5;
                       } else {
                         typ$2 = t2$3._0;
-                        exit$5 = 8;
+                        exit$5 = 6;
                       }
                       break;
                   case "RKoopaShell" :
                       if (typeof t2$3 !== "object") {
-                        exit$5 = t2$3 === "Brick" ? 7 : 6;
+                        if (t2$3 === "Brick") {
+                          dec_health(o2$6);
+                          reverse_left_right(o1$4);
+                          return [
+                            undefined,
+                            undefined
+                          ];
+                        }
+                        exit$5 = 5;
                       } else {
                         typ$2 = t2$3._0;
-                        exit$5 = 8;
+                        exit$5 = 6;
                       }
                       break;
                   default:
-                    exit$5 = 6;
+                    exit$5 = 5;
                 }
                 switch (exit$5) {
-                  case 6 :
-                      rev_dir(o1$5, t1, s1$3);
-                      return [
-                        undefined,
-                        undefined
-                      ];
-                  case 7 :
-                      dec_health(o2$6);
-                      reverse_left_right(o1$5);
+                  case 5 :
+                      rev_dir(o1$4, t1, s1$3);
                       return [
                         undefined,
                         undefined
                       ];
-                  case 8 :
+                  case 6 :
                       let updated_block$1 = evolve_block(o2$6, context);
-                      let spawned_item$1 = spawn_above(o1$5.dir, o2$6, typ$2, context);
-                      rev_dir(o1$5, t1, s1$3);
+                      let spawned_item$1 = spawn_above(o1$4.dir, o2$6, typ$2, context);
+                      rev_dir(o1$4, t1, s1$3);
                       return [
                         updated_block$1,
                         spawned_item$1
@@ -1979,9 +1988,11 @@ function process_collision(dir, c1, c2, state) {
               switch (dir) {
                 case "North" :
                 case "South" :
-                    o1$3 = o2$7;
-                    exit = 4;
-                    break;
+                    collide_block(undefined, dir, o2$7);
+                    return [
+                      undefined,
+                      undefined
+                    ];
                 case "East" :
                 case "West" :
                     reverse_left_right(o2$7);
@@ -1991,7 +2002,6 @@ function process_collision(dir, c1, c2, state) {
                     ];
                 
               }
-              break;
           
         }
         break;
@@ -2076,7 +2086,7 @@ function process_collision(dir, c1, c2, state) {
               ];
           case "FireFlower" :
           case "Star" :
-              exit$6 = 5;
+              exit$6 = 4;
               break;
           case "Coin" :
               state.coins = state.coins + 1 | 0;
@@ -2088,7 +2098,7 @@ function process_collision(dir, c1, c2, state) {
               ];
           
         }
-        if (exit$6 === 5) {
+        if (exit$6 === 4) {
           dec_health(o2$2);
           update_score(state, 1000);
           return [
@@ -2097,12 +2107,6 @@ function process_collision(dir, c1, c2, state) {
           ];
         }
         break;
-    case 4 :
-        collide_block(undefined, dir, o1$3);
-        return [
-          undefined,
-          undefined
-        ];
     
   }
 }
diff --git a/jscomp/test/marshal.js b/jscomp/test/marshal.js
index dc884923cd..5a1dcc9aff 100644
--- a/jscomp/test/marshal.js
+++ b/jscomp/test/marshal.js
@@ -5,27 +5,27 @@ let Bytes = require("../../lib/js/bytes.js");
 let Caml_external_polyfill = require("../../lib/js/caml_external_polyfill.js");
 
 function to_buffer(buff, ofs, len, v, flags) {
-  if (!(ofs < 0 || len < 0 || ofs > (buff.length - len | 0))) {
-    return Caml_external_polyfill.resolve("output_value_to_buffer")(buff, ofs, len, v, flags);
+  if (ofs < 0 || len < 0 || ofs > (buff.length - len | 0)) {
+    throw new Error("Invalid_argument", {
+          cause: {
+            RE_EXN_ID: "Invalid_argument",
+            _1: "Marshal.to_buffer: substring out of bounds"
+          }
+        });
   }
-  throw new Error("Invalid_argument", {
-        cause: {
-          RE_EXN_ID: "Invalid_argument",
-          _1: "Marshal.to_buffer: substring out of bounds"
-        }
-      });
+  return Caml_external_polyfill.resolve("output_value_to_buffer")(buff, ofs, len, v, flags);
 }
 
 function data_size(buff, ofs) {
-  if (!(ofs < 0 || ofs > (buff.length - 20 | 0))) {
-    return Caml_external_polyfill.resolve("marshal_data_size")(buff, ofs);
+  if (ofs < 0 || ofs > (buff.length - 20 | 0)) {
+    throw new Error("Invalid_argument", {
+          cause: {
+            RE_EXN_ID: "Invalid_argument",
+            _1: "Marshal.data_size"
+          }
+        });
   }
-  throw new Error("Invalid_argument", {
-        cause: {
-          RE_EXN_ID: "Invalid_argument",
-          _1: "Marshal.data_size"
-        }
-      });
+  return Caml_external_polyfill.resolve("marshal_data_size")(buff, ofs);
 }
 
 function total_size(buff, ofs) {
@@ -42,15 +42,15 @@ function from_bytes(buff, ofs) {
         });
   }
   let len = Caml_external_polyfill.resolve("marshal_data_size")(buff, ofs);
-  if (ofs <= (buff.length - (20 + len | 0) | 0)) {
-    return Caml_external_polyfill.resolve("input_value_from_string")(buff, ofs);
+  if (ofs > (buff.length - (20 + len | 0) | 0)) {
+    throw new Error("Invalid_argument", {
+          cause: {
+            RE_EXN_ID: "Invalid_argument",
+            _1: "Marshal.from_bytes"
+          }
+        });
   }
-  throw new Error("Invalid_argument", {
-        cause: {
-          RE_EXN_ID: "Invalid_argument",
-          _1: "Marshal.from_bytes"
-        }
-      });
+  return Caml_external_polyfill.resolve("input_value_from_string")(buff, ofs);
 }
 
 function from_string(buff, ofs) {
diff --git a/jscomp/test/mpr_6033_test.js b/jscomp/test/mpr_6033_test.js
index a0b19a29a0..9c1d14ef49 100644
--- a/jscomp/test/mpr_6033_test.js
+++ b/jscomp/test/mpr_6033_test.js
@@ -2,7 +2,6 @@
 'use strict';
 
 let Mt = require("./mt.js");
-let Lazy = require("../../lib/js/lazy.js");
 let CamlinternalLazy = require("../../lib/js/camlinternalLazy.js");
 
 let suites = {
@@ -34,7 +33,7 @@ function f(x) {
   return CamlinternalLazy.force(x) + "abc";
 }
 
-let x = Lazy.from_fun(function () {
+let x = CamlinternalLazy.from_fun(function () {
   return "def";
 });
 
@@ -51,4 +50,4 @@ exports.test_id = test_id;
 exports.eq = eq;
 exports.f = f;
 exports.u = u;
-/* x Not a pure module */
+/*  Not a pure module */
diff --git a/jscomp/test/number_lexer.js b/jscomp/test/number_lexer.js
index 74309374ea..abd9c0a68c 100644
--- a/jscomp/test/number_lexer.js
+++ b/jscomp/test/number_lexer.js
@@ -120,10 +120,6 @@ let __ocaml_lex_tables = {
   lex_code: ""
 };
 
-function token(l, lexbuf) {
-  __ocaml_lex_token_rec(l, lexbuf, 0);
-}
-
 function __ocaml_lex_token_rec(l, lexbuf, ___ocaml_lex_state) {
   while(true) {
     let __ocaml_lex_state = ___ocaml_lex_state;
@@ -131,33 +127,42 @@ function __ocaml_lex_token_rec(l, lexbuf, ___ocaml_lex_state) {
     switch (__ocaml_lex_state$1) {
       case 0 :
           l("new line");
-          return token(l, lexbuf);
+          ___ocaml_lex_state = 0;
+          continue;
       case 1 :
           l("number");
           l(Lexing.lexeme(lexbuf));
-          return token(l, lexbuf);
+          ___ocaml_lex_state = 0;
+          continue;
       case 2 :
           l("ident");
           l(Lexing.lexeme(lexbuf));
-          return token(l, lexbuf);
+          ___ocaml_lex_state = 0;
+          continue;
       case 3 :
           l("+");
-          return token(l, lexbuf);
+          ___ocaml_lex_state = 0;
+          continue;
       case 4 :
           l("-");
-          return token(l, lexbuf);
+          ___ocaml_lex_state = 0;
+          continue;
       case 5 :
           l("*");
-          return token(l, lexbuf);
+          ___ocaml_lex_state = 0;
+          continue;
       case 6 :
           l("/");
-          return token(l, lexbuf);
+          ___ocaml_lex_state = 0;
+          continue;
       case 7 :
           l("(");
-          return token(l, lexbuf);
+          ___ocaml_lex_state = 0;
+          continue;
       case 8 :
           l(")");
-          return token(l, lexbuf);
+          ___ocaml_lex_state = 0;
+          continue;
       case 9 :
           return l("eof");
       default:
@@ -168,6 +173,10 @@ function __ocaml_lex_token_rec(l, lexbuf, ___ocaml_lex_state) {
   };
 }
 
+function token(l, lexbuf) {
+  __ocaml_lex_token_rec(l, lexbuf, 0);
+}
+
 exports.l = l;
 exports.__ocaml_lex_tables = __ocaml_lex_tables;
 exports.token = token;
diff --git a/jscomp/test/ocaml_re_test.js b/jscomp/test/ocaml_re_test.js
index 4db87f87cc..dfcd0828f2 100644
--- a/jscomp/test/ocaml_re_test.js
+++ b/jscomp/test/ocaml_re_test.js
@@ -211,10 +211,6 @@ function single(c) {
   };
 }
 
-function add(c, l) {
-  return union(single(c), l);
-}
-
 function seq(c, c$p) {
   if (Caml_obj.lessequal(c, c$p)) {
     return {
@@ -384,7 +380,7 @@ function bal(l, x, d, r) {
       });
 }
 
-function add$1(x, data, param) {
+function add(x, data, param) {
   if (typeof param !== "object") {
     return {
       TAG: "Node",
@@ -415,14 +411,14 @@ function add$1(x, data, param) {
     }
   }
   if (c < 0) {
-    let ll = add$1(x, data, l);
+    let ll = add(x, data, l);
     if (l === ll) {
       return param;
     } else {
       return bal(ll, v, d, r);
     }
   }
-  let rr = add$1(x, data, r);
+  let rr = add(x, data, r);
   if (r === rr) {
     return param;
   } else {
@@ -430,10 +426,6 @@ function add$1(x, data, param) {
   }
 }
 
-function fold_right(t, init, f) {
-  return List.fold_right(f, t, init);
-}
-
 let cany = {
   hd: [
     0,
@@ -586,7 +578,7 @@ function bal$1(l, v, r) {
       });
 }
 
-function add$2(x, param) {
+function add$1(x, param) {
   if (typeof param !== "object") {
     return {
       TAG: "Node",
@@ -604,14 +596,14 @@ function add$2(x, param) {
     return param;
   }
   if (c < 0) {
-    let ll = add$2(x, l);
+    let ll = add$1(x, l);
     if (l === ll) {
       return param;
     } else {
       return bal$1(ll, v, r);
     }
   }
-  let rr = add$2(x, r);
+  let rr = add$1(x, r);
   if (r === rr) {
     return param;
   } else {
@@ -781,20 +773,6 @@ function rep(ids, kind, sem, x) {
   });
 }
 
-function mark(ids, m) {
-  return mk_expr(ids, {
-    TAG: "Mark",
-    _0: m
-  });
-}
-
-function pmark(ids, i) {
-  return mk_expr(ids, {
-    TAG: "Pmark",
-    _0: i
-  });
-}
-
 function erase(ids, m, m$p) {
   return mk_expr(ids, {
     TAG: "Erase",
@@ -803,20 +781,6 @@ function erase(ids, m, m$p) {
   });
 }
 
-function before(ids, c) {
-  return mk_expr(ids, {
-    TAG: "Before",
-    _0: c
-  });
-}
-
-function after(ids, c) {
-  return mk_expr(ids, {
-    TAG: "After",
-    _0: c
-  });
-}
-
 function rename(ids, x) {
   let l = x.def;
   if (typeof l !== "object") {
@@ -1109,7 +1073,12 @@ function split_at_match_rec(_l$p, _x) {
       switch (x$1.TAG) {
         case "TSeq" :
         case "TExp" :
-            break;
+            _x = x.tl;
+            _l$p = {
+              hd: x$1,
+              tl: l$p
+            };
+            continue;
         case "TMatch" :
             return [
               List.rev(l$p),
@@ -1117,23 +1086,18 @@ function split_at_match_rec(_l$p, _x) {
             ];
         
       }
-      _x = x.tl;
-      _l$p = {
-        hd: x$1,
-        tl: l$p
-      };
-      continue;
+    } else {
+      throw new Error("Assert_failure", {
+            cause: {
+              RE_EXN_ID: "Assert_failure",
+              _1: [
+                "ocaml_re_test.res",
+                816,
+                16
+              ]
+            }
+          });
     }
-    throw new Error("Assert_failure", {
-          cause: {
-            RE_EXN_ID: "Assert_failure",
-            _1: [
-              "ocaml_re_test.res",
-              816,
-              16
-            ]
-          }
-        });
   };
 }
 
@@ -1380,7 +1344,7 @@ function delta_1(marks, c, next_cat, prev_cat, x, rem) {
         }
     case "Pmark" :
         let marks_marks$1 = marks.marks;
-        let marks_pmarks$1 = add$2(s._0, marks.pmarks);
+        let marks_pmarks$1 = add$1(s._0, marks.pmarks);
         let marks$2 = {
           marks: marks_marks$1,
           pmarks: marks_pmarks$1
@@ -1768,7 +1732,7 @@ function scan_str(info, s, initial_state, groups) {
 }
 
 function cadd(c, s) {
-  return add(c, s);
+  return union(single(c), s);
 }
 
 function trans_set(cache, cm, s) {
@@ -1803,10 +1767,10 @@ function trans_set(cache, cm, s) {
   catch (raw_exn){
     let exn = Caml_js_exceptions.internalToOCamlException(raw_exn);
     if (exn.RE_EXN_ID === "Not_found") {
-      let l = fold_right(s, /* [] */0, (function (param, l) {
+      let l = List.fold_right((function (param, l) {
         return union(seq(Caml_bytes.get(cm, param[0]), Caml_bytes.get(cm, param[1])), l);
-      }));
-      cache.contents = add$1(v, l, cache.contents);
+      }), s, /* [] */0);
+      cache.contents = add(v, l, cache.contents);
       return l;
     }
     throw new Error(exn.RE_EXN_ID, {
@@ -1836,7 +1800,7 @@ function is_charset(_x) {
       case "Alternative" :
       case "Intersection" :
       case "Complement" :
-          break;
+          return List.for_all(is_charset, x._0);
       case "Difference" :
           if (!is_charset(x._0)) {
             return false;
@@ -1846,7 +1810,6 @@ function is_charset(_x) {
       default:
         return false;
     }
-    return List.for_all(is_charset, x._0);
   };
 }
 
@@ -1893,7 +1856,13 @@ let cdigit = seq(/* '0' */48, /* '9' */57);
 
 let calnum = union(calpha, cdigit);
 
-let cword = add(/* '_' */95, calnum);
+let cword = union({
+  hd: [
+    /* '_' */95,
+    /* '_' */95
+  ],
+  tl: /* [] */0
+}, calnum);
 
 function colorize(c, regexp) {
   let lnl = {
@@ -2334,31 +2303,67 @@ function translate(ids, kind, _ign_group, ign_case, _greedy, pos, cache, c, _x)
     if (typeof x !== "object") {
       switch (x) {
         case "Beg_of_line" :
+            let c$1 = Re_automata_Category.$plus$plus(Re_automata_Category.inexistant, Re_automata_Category.newline);
             return [
-              after(ids, Re_automata_Category.$plus$plus(Re_automata_Category.inexistant, Re_automata_Category.newline)),
+              mk_expr(ids, {
+                TAG: "After",
+                _0: c$1
+              }),
               kind
             ];
         case "End_of_line" :
+            let c$2 = Re_automata_Category.$plus$plus(Re_automata_Category.inexistant, Re_automata_Category.newline);
             return [
-              before(ids, Re_automata_Category.$plus$plus(Re_automata_Category.inexistant, Re_automata_Category.newline)),
+              mk_expr(ids, {
+                TAG: "Before",
+                _0: c$2
+              }),
               kind
             ];
         case "Beg_of_word" :
+            let c$3 = Re_automata_Category.$plus$plus(Re_automata_Category.inexistant, Re_automata_Category.not_letter);
+            let c$4 = Re_automata_Category.$plus$plus(Re_automata_Category.inexistant, Re_automata_Category.letter);
             return [
-              seq$1(ids, "First", after(ids, Re_automata_Category.$plus$plus(Re_automata_Category.inexistant, Re_automata_Category.not_letter)), before(ids, Re_automata_Category.$plus$plus(Re_automata_Category.inexistant, Re_automata_Category.letter))),
+              seq$1(ids, "First", mk_expr(ids, {
+                TAG: "After",
+                _0: c$3
+              }), mk_expr(ids, {
+                TAG: "Before",
+                _0: c$4
+              })),
               kind
             ];
         case "End_of_word" :
+            let c$5 = Re_automata_Category.$plus$plus(Re_automata_Category.inexistant, Re_automata_Category.letter);
+            let c$6 = Re_automata_Category.$plus$plus(Re_automata_Category.inexistant, Re_automata_Category.not_letter);
             return [
-              seq$1(ids, "First", after(ids, Re_automata_Category.$plus$plus(Re_automata_Category.inexistant, Re_automata_Category.letter)), before(ids, Re_automata_Category.$plus$plus(Re_automata_Category.inexistant, Re_automata_Category.not_letter))),
+              seq$1(ids, "First", mk_expr(ids, {
+                TAG: "After",
+                _0: c$5
+              }), mk_expr(ids, {
+                TAG: "Before",
+                _0: c$6
+              })),
               kind
             ];
         case "Not_bound" :
             return [
               alt(ids, {
-                hd: seq$1(ids, "First", after(ids, Re_automata_Category.letter), before(ids, Re_automata_Category.letter)),
+                hd: seq$1(ids, "First", mk_expr(ids, {
+                  TAG: "After",
+                  _0: Re_automata_Category.letter
+                }), mk_expr(ids, {
+                  TAG: "Before",
+                  _0: Re_automata_Category.letter
+                })),
                 tl: {
-                  hd: seq$1(ids, "First", after(ids, Re_automata_Category.letter), before(ids, Re_automata_Category.letter)),
+                  hd: seq$1(ids, "First", mk_expr(ids, {
+                    TAG: "After",
+                    _0: Re_automata_Category.letter
+                  }), mk_expr(ids, {
+                    TAG: "Before",
+                    _0: Re_automata_Category.letter
+                  })),
                   tl: /* [] */0
                 }
               }),
@@ -2366,27 +2371,43 @@ function translate(ids, kind, _ign_group, ign_case, _greedy, pos, cache, c, _x)
             ];
         case "Beg_of_str" :
             return [
-              after(ids, Re_automata_Category.inexistant),
+              mk_expr(ids, {
+                TAG: "After",
+                _0: Re_automata_Category.inexistant
+              }),
               kind
             ];
         case "End_of_str" :
             return [
-              before(ids, Re_automata_Category.inexistant),
+              mk_expr(ids, {
+                TAG: "Before",
+                _0: Re_automata_Category.inexistant
+              }),
               kind
             ];
         case "Last_end_of_line" :
+            let c$7 = Re_automata_Category.$plus$plus(Re_automata_Category.inexistant, Re_automata_Category.lastnewline);
             return [
-              before(ids, Re_automata_Category.$plus$plus(Re_automata_Category.inexistant, Re_automata_Category.lastnewline)),
+              mk_expr(ids, {
+                TAG: "Before",
+                _0: c$7
+              }),
               kind
             ];
         case "Start" :
             return [
-              after(ids, Re_automata_Category.search_boundary),
+              mk_expr(ids, {
+                TAG: "After",
+                _0: Re_automata_Category.search_boundary
+              }),
               kind
             ];
         case "Stop" :
             return [
-              before(ids, Re_automata_Category.search_boundary),
+              mk_expr(ids, {
+                TAG: "Before",
+                _0: Re_automata_Category.search_boundary
+              }),
               kind
             ];
         
@@ -2475,7 +2496,13 @@ function translate(ids, kind, _ign_group, ign_case, _greedy, pos, cache, c, _x)
             pos.contents = pos.contents + 2 | 0;
             let match$3 = translate(ids, kind, ign_group, ign_case, greedy, pos, cache, c, r$p);
             return [
-              seq$1(ids, "First", mark(ids, p), seq$1(ids, "First", match$3[0], mark(ids, p + 1 | 0))),
+              seq$1(ids, "First", mk_expr(ids, {
+                TAG: "Mark",
+                _0: p
+              }), seq$1(ids, "First", match$3[0], mk_expr(ids, {
+                TAG: "Mark",
+                _0: p + 1 | 0
+              }))),
               match$3[1]
             ];
         case "No_group" :
@@ -2502,7 +2529,10 @@ function translate(ids, kind, _ign_group, ign_case, _greedy, pos, cache, c, _x)
         case "Pmark" :
             let match$5 = translate(ids, kind, ign_group, ign_case, greedy, pos, cache, c, x._1);
             return [
-              seq$1(ids, "First", pmark(ids, x._0), match$5[0]),
+              seq$1(ids, "First", mk_expr(ids, {
+                TAG: "Pmark",
+                _0: x._0
+              }), match$5[0]),
               match$5[1]
             ];
         default:
@@ -2808,18 +2838,6 @@ function repn(r, i, j) {
   };
 }
 
-function rep$1(r) {
-  return repn(r, 0, undefined);
-}
-
-function rep1(r) {
-  return repn(r, 1, undefined);
-}
-
-function opt(r) {
-  return repn(r, 0, 1);
-}
-
 function set(str) {
   let s = /* [] */0;
   for(let i = 0 ,i_finish = str.length; i < i_finish; ++i){
@@ -2831,13 +2849,6 @@ function set(str) {
   };
 }
 
-function rg(c, c$p) {
-  return {
-    TAG: "Set",
-    _0: seq(c, c$p)
-  };
-}
-
 function compl(l) {
   let r = {
     TAG: "Complement",
@@ -2871,7 +2882,10 @@ let notnl = {
 };
 
 let lower = alt$1({
-  hd: rg(/* 'a' */97, /* 'z' */122),
+  hd: {
+    TAG: "Set",
+    _0: seq(/* 'a' */97, /* 'z' */122)
+  },
   tl: {
     hd: {
       TAG: "Set",
@@ -2884,9 +2898,15 @@ let lower = alt$1({
       }
     },
     tl: {
-      hd: rg(/* '\223' */223, /* '\246' */246),
+      hd: {
+        TAG: "Set",
+        _0: seq(/* '\223' */223, /* '\246' */246)
+      },
       tl: {
-        hd: rg(/* '\248' */248, /* '\255' */255),
+        hd: {
+          TAG: "Set",
+          _0: seq(/* '\248' */248, /* '\255' */255)
+        },
         tl: /* [] */0
       }
     }
@@ -2894,11 +2914,20 @@ let lower = alt$1({
 });
 
 let upper = alt$1({
-  hd: rg(/* 'A' */65, /* 'Z' */90),
+  hd: {
+    TAG: "Set",
+    _0: seq(/* 'A' */65, /* 'Z' */90)
+  },
   tl: {
-    hd: rg(/* '\192' */192, /* '\214' */214),
+    hd: {
+      TAG: "Set",
+      _0: seq(/* '\192' */192, /* '\214' */214)
+    },
     tl: {
-      hd: rg(/* '\216' */216, /* '\222' */222),
+      hd: {
+        TAG: "Set",
+        _0: seq(/* '\216' */216, /* '\222' */222)
+      },
       tl: /* [] */0
     }
   }
@@ -2936,7 +2965,10 @@ let alpha = alt$1({
   }
 });
 
-let digit = rg(/* '0' */48, /* '9' */57);
+let digit = {
+  TAG: "Set",
+  _0: seq(/* '0' */48, /* '9' */57)
+};
 
 let alnum = alt$1({
   hd: alpha,
@@ -2963,50 +2995,95 @@ let wordc = alt$1({
   }
 });
 
-let ascii = rg(/* '\000' */0, /* '\127' */127);
+let ascii = {
+  TAG: "Set",
+  _0: seq(/* '\000' */0, /* '\127' */127)
+};
 
 let blank = set("\t ");
 
 let cntrl = alt$1({
-  hd: rg(/* '\000' */0, /* '\031' */31),
+  hd: {
+    TAG: "Set",
+    _0: seq(/* '\000' */0, /* '\031' */31)
+  },
   tl: {
-    hd: rg(/* '\127' */127, /* '\159' */159),
+    hd: {
+      TAG: "Set",
+      _0: seq(/* '\127' */127, /* '\159' */159)
+    },
     tl: /* [] */0
   }
 });
 
 let graph = alt$1({
-  hd: rg(/* '!' */33, /* '~' */126),
+  hd: {
+    TAG: "Set",
+    _0: seq(/* '!' */33, /* '~' */126)
+  },
   tl: {
-    hd: rg(/* '\160' */160, /* '\255' */255),
+    hd: {
+      TAG: "Set",
+      _0: seq(/* '\160' */160, /* '\255' */255)
+    },
     tl: /* [] */0
   }
 });
 
 let print = alt$1({
-  hd: rg(/* ' ' */32, /* '~' */126),
+  hd: {
+    TAG: "Set",
+    _0: seq(/* ' ' */32, /* '~' */126)
+  },
   tl: {
-    hd: rg(/* '\160' */160, /* '\255' */255),
+    hd: {
+      TAG: "Set",
+      _0: seq(/* '\160' */160, /* '\255' */255)
+    },
     tl: /* [] */0
   }
 });
 
 let punct = alt$1({
-  hd: rg(/* '!' */33, /* '/' */47),
+  hd: {
+    TAG: "Set",
+    _0: seq(/* '!' */33, /* '/' */47)
+  },
   tl: {
-    hd: rg(/* ':' */58, /* '@' */64),
+    hd: {
+      TAG: "Set",
+      _0: seq(/* ':' */58, /* '@' */64)
+    },
     tl: {
-      hd: rg(/* '[' */91, /* '`' */96),
+      hd: {
+        TAG: "Set",
+        _0: seq(/* '[' */91, /* '`' */96)
+      },
       tl: {
-        hd: rg(/* '{' */123, /* '~' */126),
+        hd: {
+          TAG: "Set",
+          _0: seq(/* '{' */123, /* '~' */126)
+        },
         tl: {
-          hd: rg(/* '\160' */160, /* '\169' */169),
+          hd: {
+            TAG: "Set",
+            _0: seq(/* '\160' */160, /* '\169' */169)
+          },
           tl: {
-            hd: rg(/* '\171' */171, /* '\180' */180),
+            hd: {
+              TAG: "Set",
+              _0: seq(/* '\171' */171, /* '\180' */180)
+            },
             tl: {
-              hd: rg(/* '\182' */182, /* '\185' */185),
+              hd: {
+                TAG: "Set",
+                _0: seq(/* '\182' */182, /* '\185' */185)
+              },
               tl: {
-                hd: rg(/* '\187' */187, /* '\191' */191),
+                hd: {
+                  TAG: "Set",
+                  _0: seq(/* '\187' */187, /* '\191' */191)
+                },
                 tl: {
                   hd: {
                     TAG: "Set",
@@ -3053,7 +3130,10 @@ let space = alt$1({
     }
   },
   tl: {
-    hd: rg(/* '\t' */9, /* '\r' */13),
+    hd: {
+      TAG: "Set",
+      _0: seq(/* '\t' */9, /* '\r' */13)
+    },
     tl: /* [] */0
   }
 });
@@ -3061,14 +3141,73 @@ let space = alt$1({
 let xdigit = alt$1({
   hd: digit,
   tl: {
-    hd: rg(/* 'a' */97, /* 'f' */102),
+    hd: {
+      TAG: "Set",
+      _0: seq(/* 'a' */97, /* 'f' */102)
+    },
     tl: {
-      hd: rg(/* 'A' */65, /* 'F' */70),
+      hd: {
+        TAG: "Set",
+        _0: seq(/* 'A' */65, /* 'F' */70)
+      },
       tl: /* [] */0
     }
   }
 });
 
+function compile(r) {
+  let regexp = anchored(r) ? ({
+      TAG: "Group",
+      _0: r
+    }) : seq$2({
+      hd: {
+        TAG: "Sem",
+        _0: "Shortest",
+        _1: repn(any, 0, undefined)
+      },
+      tl: {
+        hd: {
+          TAG: "Group",
+          _0: r
+        },
+        tl: /* [] */0
+      }
+    });
+  let regexp$1 = handle_case(false, regexp);
+  let c = Bytes.make(257, /* '\000' */0);
+  let need_lnl = colorize(c, regexp$1);
+  let match = flatten_cmap(c);
+  let ncol = match[2];
+  let col = match[0];
+  let lnl = need_lnl ? ncol : -1;
+  let ncol$1 = need_lnl ? ncol + 1 | 0 : ncol;
+  let ids = {
+    contents: 0
+  };
+  let pos = {
+    contents: 0
+  };
+  let match$1 = translate(ids, "First", false, false, "Greedy", pos, {
+    contents: "Empty"
+  }, col, regexp$1);
+  let r$1 = enforce_kind(ids, "First", match$1[1], match$1[0]);
+  let col_repr = match[1];
+  let group_count = pos.contents / 2 | 0;
+  return {
+    initial: r$1,
+    initial_states: /* [] */0,
+    cols: col,
+    col_repr: col_repr,
+    ncol: ncol$1,
+    lnl: lnl,
+    tbl: {
+      contents: [false]
+    },
+    states: Re_automata_State.Table.create(97),
+    group_count: group_count
+  };
+}
+
 function exec_internal(name, posOpt, lenOpt, groups, re, s) {
   let pos = posOpt !== undefined ? posOpt : 0;
   let len = lenOpt !== undefined ? lenOpt : -1;
@@ -3205,10 +3344,11 @@ function posix_class_of_string(x) {
     case "xdigit" :
         return xdigit;
     default:
+      let s = "Invalid pcre class: " + x;
       throw new Error("Invalid_argument", {
             cause: {
               RE_EXN_ID: "Invalid_argument",
-              _1: "Invalid pcre class: " + x
+              _1: s
             }
           });
   }
@@ -3290,8 +3430,7 @@ function parse(multiline, dollar_endonly, dotall, ungreedy, s) {
       };
     }
   };
-  let regexp = function () {
-    let _left = branch$p(/* [] */0);
+  let regexp$p = function (_left) {
     while(true) {
       let left = _left;
       if (!accept(/* '|' */124)) {
@@ -3331,7 +3470,7 @@ function parse(multiline, dollar_endonly, dotall, ungreedy, s) {
     if (accept(/* '(' */40)) {
       if (accept(/* '?' */63)) {
         if (accept(/* ':' */58)) {
-          let r = regexp();
+          let r = regexp$p(branch());
           if (!accept(/* ')' */41)) {
             throw new Error(Parse_error, {
                   cause: {
@@ -3350,7 +3489,7 @@ function parse(multiline, dollar_endonly, dotall, ungreedy, s) {
               }
             });
       }
-      let r$1 = regexp();
+      let r$1 = regexp$p(branch());
       if (!accept(/* ')' */41)) {
         throw new Error(Parse_error, {
               cause: {
@@ -3619,13 +3758,13 @@ function parse(multiline, dollar_endonly, dotall, ungreedy, s) {
   let piece = function () {
     let r = atom();
     if (accept(/* '*' */42)) {
-      return greedy_mod(rep$1(r));
+      return greedy_mod(repn(r, 0, undefined));
     }
     if (accept(/* '+' */43)) {
-      return greedy_mod(rep1(r));
+      return greedy_mod(repn(r, 1, undefined));
     }
     if (accept(/* '?' */63)) {
-      return greedy_mod(opt(r));
+      return greedy_mod(repn(r, 0, 1));
     }
     if (!accept(/* '{' */123)) {
       return r;
@@ -4015,7 +4154,10 @@ function parse(multiline, dollar_endonly, dotall, ungreedy, s) {
             };
           }
           _s = {
-            hd: rg(c, match$1.VAL),
+            hd: {
+              TAG: "Set",
+              _0: seq(c, match$1.VAL)
+            },
             tl: s
           };
           continue;
@@ -4036,6 +4178,9 @@ function parse(multiline, dollar_endonly, dotall, ungreedy, s) {
       continue;
     };
   };
+  let branch = function () {
+    return branch$p(/* [] */0);
+  };
   let comment = function () {
     while(true) {
       if (accept(/* ')' */41)) {
@@ -4046,7 +4191,7 @@ function parse(multiline, dollar_endonly, dotall, ungreedy, s) {
       continue;
     };
   };
-  let res = regexp();
+  let res = regexp$p(branch());
   if (i.contents !== l) {
     throw new Error(Parse_error, {
           cause: {
@@ -4088,60 +4233,6 @@ function re(flagsOpt, pat) {
   }
 }
 
-function regexp(flags, pat) {
-  let r = re(flags, pat);
-  let regexp$1 = anchored(r) ? ({
-      TAG: "Group",
-      _0: r
-    }) : seq$2({
-      hd: {
-        TAG: "Sem",
-        _0: "Shortest",
-        _1: rep$1(any)
-      },
-      tl: {
-        hd: {
-          TAG: "Group",
-          _0: r
-        },
-        tl: /* [] */0
-      }
-    });
-  let regexp$2 = handle_case(false, regexp$1);
-  let c = Bytes.make(257, /* '\000' */0);
-  let need_lnl = colorize(c, regexp$2);
-  let match = flatten_cmap(c);
-  let ncol = match[2];
-  let col = match[0];
-  let lnl = need_lnl ? ncol : -1;
-  let ncol$1 = need_lnl ? ncol + 1 | 0 : ncol;
-  let ids = {
-    contents: 0
-  };
-  let pos = {
-    contents: 0
-  };
-  let match$1 = translate(ids, "First", false, false, "Greedy", pos, {
-    contents: "Empty"
-  }, col, regexp$2);
-  let r$1 = enforce_kind(ids, "First", match$1[1], match$1[0]);
-  let col_repr = match[1];
-  let group_count = pos.contents / 2 | 0;
-  return {
-    initial: r$1,
-    initial_states: /* [] */0,
-    cols: col,
-    col_repr: col_repr,
-    ncol: ncol$1,
-    lnl: lnl,
-    tbl: {
-      contents: [false]
-    },
-    states: Re_automata_State.Table.create(97),
-    group_count: group_count
-  };
-}
-
 function exec(rex, pos, s) {
   let len;
   let substr = exec_internal("Re.exec", pos, len, true, rex, s);
@@ -4164,7 +4255,7 @@ function exec(rex, pos, s) {
 
 let s = "a".repeat(1048575) + "b";
 
-eq("File \"ocaml_re_test.res\", line 3843, characters 7-14", get(exec(regexp(undefined, "aa?b"), undefined, s), 0), "aab");
+eq("File \"ocaml_re_test.res\", line 3843, characters 7-14", get(exec(compile(re(undefined, "aa?b")), undefined, s), 0), "aab");
 
 Mt.from_pair_suites("Ocaml_re_test", suites.contents);
 
diff --git a/jscomp/test/pipe_syntax.js b/jscomp/test/pipe_syntax.js
index 868d41895b..79f97aeb38 100644
--- a/jscomp/test/pipe_syntax.js
+++ b/jscomp/test/pipe_syntax.js
@@ -43,12 +43,10 @@ function f2(a, b, c, d) {
 
 function f3(a, b, c, d, e) {
   let __tuple_internal_obj = a(b);
-  let param = [
-    c(__tuple_internal_obj, d),
-    d(__tuple_internal_obj, 1, 2),
-    e(__tuple_internal_obj)
-  ];
-  return (param[0] + param[1] | 0) + param[2] | 0;
+  let param_0 = c(__tuple_internal_obj, d);
+  let param_1 = d(__tuple_internal_obj, 1, 2);
+  let param_2 = e(__tuple_internal_obj);
+  return (param_0 + param_1 | 0) + param_2 | 0;
 }
 
 function f4(a, b, c) {
diff --git a/jscomp/test/ppx_apply_test.js b/jscomp/test/ppx_apply_test.js
index e3c501ddfe..c8d27383ce 100644
--- a/jscomp/test/ppx_apply_test.js
+++ b/jscomp/test/ppx_apply_test.js
@@ -56,4 +56,4 @@ exports.nullary = nullary;
 exports.unary = unary;
 exports.xx = xx;
 exports.h = h;
-/* u Not a pure module */
+/*  Not a pure module */
diff --git a/jscomp/test/random_test.js b/jscomp/test/random_test.js
index 2aa27ff159..c17e6947e0 100644
--- a/jscomp/test/random_test.js
+++ b/jscomp/test/random_test.js
@@ -33,9 +33,7 @@ function approx(f) {
   };
 }
 
-((function (extra, extra$1) {
-    return Mt_global.collect_neq(id, suites, "File \"random_test.res\", line 9, characters 2-9", extra, extra$1);
-  })((Random.self_init(), Random.int(10000)), (Random.self_init(), Random.int(1000))));
+Mt_global.collect_neq(id, suites, "File \"random_test.res\", line 9, characters 2-9", (Random.self_init(), Random.int(10000)), (Random.self_init(), Random.int(1000)));
 
 Random.init(0);
 
@@ -45,20 +43,18 @@ for(let i = 0; i <= 9; ++i){
   Caml_array.set(v, i, Random.bool());
 }
 
-((function (extra, extra$1) {
-    return Mt_global.collect_eq(id, suites, "File \"random_test.res\", line 28, characters 12-19", extra, extra$1);
-  })(v, [
-    true,
-    true,
-    true,
-    true,
-    true,
-    false,
-    true,
-    true,
-    true,
-    false
-  ]));
+Mt_global.collect_eq(id, suites, "File \"random_test.res\", line 28, characters 12-19", v, [
+  true,
+  true,
+  true,
+  true,
+  true,
+  false,
+  true,
+  true,
+  true,
+  false
+]);
 
 let f = Random.int64(Int64.max_int);
 
diff --git a/jscomp/test/raw_output_test.js b/jscomp/test/raw_output_test.js
index 9322ea7fd8..156dcbbf3f 100644
--- a/jscomp/test/raw_output_test.js
+++ b/jscomp/test/raw_output_test.js
@@ -8,9 +8,7 @@ function mk(fn) {
 
 (((_)=> console.log('should works'))());
 
-console.log((function () {
-  return 1;
-})());
+console.log(1);
 
 exports.mk = mk;
 /*  Not a pure module */
diff --git a/jscomp/test/reasonReact.js b/jscomp/test/reasonReact.js
index fcd2352d0f..49bd1161a1 100644
--- a/jscomp/test/reasonReact.js
+++ b/jscomp/test/reasonReact.js
@@ -56,21 +56,13 @@ function basicComponent(debugName) {
   };
 }
 
-function statelessComponent(debugName) {
-  return basicComponent(debugName);
-}
+let statelessComponent = basicComponent;
 
-function statelessComponentWithRetainedProps(debugName) {
-  return basicComponent(debugName);
-}
+let statelessComponentWithRetainedProps = basicComponent;
 
-function reducerComponent(debugName) {
-  return basicComponent(debugName);
-}
+let reducerComponent = basicComponent;
 
-function reducerComponentWithRetainedProps(debugName) {
-  return basicComponent(debugName);
-}
+let reducerComponentWithRetainedProps = basicComponent;
 
 function element(keyOpt, refOpt, component) {
   let key = keyOpt !== undefined ? keyOpt : undefined;
diff --git a/jscomp/test/reasonReactCompat.js b/jscomp/test/reasonReactCompat.js
index cde9d8b3ad..43f178a76d 100644
--- a/jscomp/test/reasonReactCompat.js
+++ b/jscomp/test/reasonReactCompat.js
@@ -3,13 +3,9 @@
 
 let ReasonReact = require("./reasonReact.js");
 
-function wrapReactForReasonReact(component, props, children) {
-  return ReasonReact.wrapJsForReason(component, props, children);
-}
+let wrapReactForReasonReact = ReasonReact.wrapJsForReason;
 
-function wrapReasonReactForReact(component, propsConverter) {
-  return ReasonReact.wrapReasonForJs(component, propsConverter);
-}
+let wrapReasonReactForReact = ReasonReact.wrapReasonForJs;
 
 exports.wrapReactForReasonReact = wrapReactForReasonReact;
 exports.wrapReasonReactForReact = wrapReasonReactForReact;
diff --git a/jscomp/test/recursive_module.js b/jscomp/test/recursive_module.js
index c28f063fcd..4efd37878f 100644
--- a/jscomp/test/recursive_module.js
+++ b/jscomp/test/recursive_module.js
@@ -70,7 +70,7 @@ let Intb = Caml_module.init_mod([
     ]]
 });
 
-let a = Lazy.from_fun(function () {
+let a = CamlinternalLazy.from_fun(function () {
   return CamlinternalLazy.force(Intb.a);
 });
 
@@ -84,7 +84,7 @@ Caml_module.update_mod({
   a: a
 });
 
-let a$1 = Lazy.from_fun(function () {
+let a$1 = CamlinternalLazy.from_fun(function () {
   return CamlinternalLazy.force(Inta.a) + 1 | 0;
 });
 
@@ -140,7 +140,7 @@ let Intb$1 = Caml_module.init_mod([
     ]]
 });
 
-let a$2 = Lazy.from_fun(function () {
+let a$2 = CamlinternalLazy.from_fun(function () {
   return CamlinternalLazy.force(Intb$1.a) + 1 | 0;
 });
 
@@ -154,7 +154,7 @@ Caml_module.update_mod({
   a: a$2
 });
 
-let a$3 = Lazy.from_fun(function () {
+let a$3 = CamlinternalLazy.from_fun(function () {
   return 2;
 });
 
diff --git a/jscomp/test/sexp.js b/jscomp/test/sexp.js
index cc631d3a3a..ec021c83c3 100644
--- a/jscomp/test/sexp.js
+++ b/jscomp/test/sexp.js
@@ -12,9 +12,7 @@ let equal = Caml_obj.equal;
 
 let compare = Caml_obj.compare;
 
-function hash(a) {
-  return Hashtbl.hash(a);
-}
+let hash = Hashtbl.hash;
 
 function of_int(x) {
   return {
@@ -370,20 +368,39 @@ function get_field(name) {
           return;
         }
         let match = l.hd;
-        if (typeof match === "object" && match.NAME === "List") {
-          let match$1 = match.VAL;
-          if (match$1) {
-            let match$2 = match$1.hd;
-            if (typeof match$2 === "object" && match$2.NAME === "Atom") {
-              let match$3 = match$1.tl;
-              if (match$3 && !match$3.tl && Caml_obj.equal(name, match$2.VAL)) {
-                return match$3.hd;
+        if (typeof match === "object") {
+          if (match.NAME === "List") {
+            let match$1 = match.VAL;
+            if (match$1) {
+              let match$2 = match$1.hd;
+              if (typeof match$2 === "object") {
+                if (match$2.NAME === "Atom") {
+                  let match$3 = match$1.tl;
+                  if (match$3) {
+                    if (match$3.tl) {
+                      _l = l.tl;
+                      continue;
+                    }
+                    if (Caml_obj.equal(name, match$2.VAL)) {
+                      return match$3.hd;
+                    }
+                    _l = l.tl;
+                    continue;
+                  }
+                  _l = l.tl;
+                  continue;
+                }
+                _l = l.tl;
+                continue;
               }
-              
+              _l = l.tl;
+              continue;
             }
-            
+            _l = l.tl;
+            continue;
           }
-          
+          _l = l.tl;
+          continue;
         }
         _l = l.tl;
         continue;
@@ -406,16 +423,30 @@ function _get_field_list(name, _l) {
       return;
     }
     let match = l.hd;
-    if (typeof match === "object" && match.NAME === "List") {
-      let match$1 = match.VAL;
-      if (match$1) {
-        let match$2 = match$1.hd;
-        if (typeof match$2 === "object" && match$2.NAME === "Atom" && Caml_obj.equal(name, match$2.VAL)) {
-          return match$1.tl;
+    if (typeof match === "object") {
+      if (match.NAME === "List") {
+        let match$1 = match.VAL;
+        if (match$1) {
+          let match$2 = match$1.hd;
+          if (typeof match$2 === "object") {
+            if (match$2.NAME === "Atom") {
+              if (Caml_obj.equal(name, match$2.VAL)) {
+                return match$1.tl;
+              }
+              _l = l.tl;
+              continue;
+            }
+            _l = l.tl;
+            continue;
+          }
+          _l = l.tl;
+          continue;
         }
-        
+        _l = l.tl;
+        continue;
       }
-      
+      _l = l.tl;
+      continue;
     }
     _l = l.tl;
     continue;
@@ -521,4 +552,4 @@ exports.of_variant = of_variant;
 exports.of_field = of_field;
 exports.of_record = of_record;
 exports.Traverse = Traverse;
-/* Hashtbl Not a pure module */
+/* No side effect */
diff --git a/jscomp/test/sexpm.js b/jscomp/test/sexpm.js
index 44de13f8fd..9ac601aa21 100644
--- a/jscomp/test/sexpm.js
+++ b/jscomp/test/sexpm.js
@@ -302,7 +302,22 @@ function expr_list(acc, k, t) {
     }
     return expr_starting_with(c, (function (last, e) {
       if (last !== undefined) {
-        if (last === 40) {
+        if (last !== 40) {
+          if (last !== 41) {
+            return expr_list({
+              hd: e,
+              tl: acc
+            }, k, t);
+          } else {
+            return k(undefined, {
+              NAME: "List",
+              VAL: List.rev({
+                hd: e,
+                tl: acc
+              })
+            });
+          }
+        } else {
           return expr_list(/* [] */0, (function (param, l) {
             return expr_list({
               hd: l,
@@ -310,21 +325,12 @@ function expr_list(acc, k, t) {
             }, k, t);
           }), t);
         }
-        if (last === 41) {
-          return k(undefined, {
-            NAME: "List",
-            VAL: List.rev({
-              hd: e,
-              tl: acc
-            })
-          });
-        }
-        
+      } else {
+        return expr_list({
+          hd: e,
+          tl: acc
+        }, k, t);
       }
-      return expr_list({
-        hd: e,
-        tl: acc
-      }, k, t);
     }), t);
   };
 }
diff --git a/jscomp/test/stack_comp_test.js b/jscomp/test/stack_comp_test.js
index 5f384a3582..dabb3ee849 100644
--- a/jscomp/test/stack_comp_test.js
+++ b/jscomp/test/stack_comp_test.js
@@ -2,6 +2,7 @@
 'use strict';
 
 let Mt = require("./mt.js");
+let List = require("../../lib/js/list.js");
 let Stack = require("../../lib/js/stack.js");
 let Caml_obj = require("../../lib/js/caml_obj.js");
 let Mt_global = require("./mt_global.js");
@@ -30,12 +31,12 @@ function to_list(s) {
   let l = {
     contents: /* [] */0
   };
-  Stack.iter((function (x) {
+  List.iter((function (x) {
     l.contents = {
       hd: x,
       tl: l.contents
     };
-  }), s);
+  }), s.c);
   return l.contents;
 }
 
@@ -358,10 +359,10 @@ let i$7 = {
   contents: 1
 };
 
-Stack.iter((function (j) {
+List.iter((function (j) {
   assert_("File \"stack_comp_test.res\", line 143, characters 12-19", i$7.contents === j);
   i$7.contents = i$7.contents + 1 | 0;
-}), s$5);
+}), s$5.c);
 
 let s1$1 = {
   c: /* [] */0,
diff --git a/jscomp/test/stream_parser_test.js b/jscomp/test/stream_parser_test.js
index 63128f88f2..d8c949d0ee 100644
--- a/jscomp/test/stream_parser_test.js
+++ b/jscomp/test/stream_parser_test.js
@@ -35,7 +35,7 @@ function parse(token) {
     switch (n.TAG) {
       case "Kwd" :
           if (n._0 === "(") {
-            let v = parse_expr();
+            let v = parse_expr_aux(parse_term());
             let match = token$1();
             if (match.TAG === "Kwd") {
               if (match._0 === ")") {
@@ -75,14 +75,16 @@ function parse(token) {
     }
   };
   let parse_term = function () {
-    let e1 = parse_atom();
+    return parse_term_aux(parse_atom());
+  };
+  let parse_expr_aux = function (e1) {
     let e = token$1();
     if (e.TAG === "Kwd") {
       switch (e._0) {
-        case "*" :
-            return Math.imul(e1, parse_term());
-        case "/" :
-            return Caml_int32.div(e1, parse_term());
+        case "+" :
+            return e1 + parse_expr_aux(parse_term()) | 0;
+        case "-" :
+            return e1 - parse_expr_aux(parse_term()) | 0;
         default:
           Queue.push(e, look_ahead);
           return e1;
@@ -92,15 +94,14 @@ function parse(token) {
       return e1;
     }
   };
-  let parse_expr = function () {
-    let e1 = parse_term();
+  let parse_term_aux = function (e1) {
     let e = token$1();
     if (e.TAG === "Kwd") {
       switch (e._0) {
-        case "+" :
-            return e1 + parse_expr() | 0;
-        case "-" :
-            return e1 - parse_expr() | 0;
+        case "*" :
+            return Math.imul(e1, parse_term_aux(parse_atom()));
+        case "/" :
+            return Caml_int32.div(e1, parse_term_aux(parse_atom()));
         default:
           Queue.push(e, look_ahead);
           return e1;
@@ -110,7 +111,7 @@ function parse(token) {
       return e1;
     }
   };
-  let r = parse_expr();
+  let r = parse_expr_aux(parse_term());
   return [
     r,
     Queue.fold((function (acc, x) {
@@ -169,58 +170,12 @@ function l_parse(token) {
       };
     }
   };
-  let parse_e = function () {
-    let _a = parse_t();
-    while(true) {
-      let a = _a;
-      let t = token$1();
-      if (t.TAG === "Kwd") {
-        switch (t._0) {
-          case "+" :
-              _a = a + parse_t() | 0;
-              continue;
-          case "-" :
-              _a = a - parse_t() | 0;
-              continue;
-          default:
-            Queue.push(t, look_ahead);
-            return a;
-        }
-      } else {
-        Queue.push(t, look_ahead);
-        return a;
-      }
-    };
-  };
-  let parse_t = function () {
-    let _a = parse_f();
-    while(true) {
-      let a = _a;
-      let t = token$1();
-      if (t.TAG === "Kwd") {
-        switch (t._0) {
-          case "*" :
-              _a = Math.imul(a, parse_f());
-              continue;
-          case "/" :
-              _a = Caml_int32.div(a, parse_f());
-              continue;
-          default:
-            Queue.push(t, look_ahead);
-            return a;
-        }
-      } else {
-        Queue.push(t, look_ahead);
-        return a;
-      }
-    };
-  };
   let parse_f = function () {
     let i = token$1();
     switch (i.TAG) {
       case "Kwd" :
           if (i._0 === "(") {
-            let v = parse_e();
+            let v = parse_t_aux(parse_t());
             let t = token$1();
             if (t.TAG === "Kwd") {
               if (t._0 === ")") {
@@ -257,7 +212,54 @@ function l_parse(token) {
             });
     }
   };
-  let r = parse_e();
+  let parse_f_aux = function (_a) {
+    while(true) {
+      let a = _a;
+      let t = token$1();
+      if (t.TAG === "Kwd") {
+        switch (t._0) {
+          case "*" :
+              _a = Math.imul(a, parse_f());
+              continue;
+          case "/" :
+              _a = Caml_int32.div(a, parse_f());
+              continue;
+          default:
+            Queue.push(t, look_ahead);
+            return a;
+        }
+      } else {
+        Queue.push(t, look_ahead);
+        return a;
+      }
+    };
+  };
+  let parse_t_aux = function (_a) {
+    while(true) {
+      let a = _a;
+      let t = token$1();
+      if (t.TAG === "Kwd") {
+        switch (t._0) {
+          case "+" :
+              _a = a + parse_f_aux(parse_f()) | 0;
+              continue;
+          case "-" :
+              _a = a - parse_f_aux(parse_f()) | 0;
+              continue;
+          default:
+            Queue.push(t, look_ahead);
+            return a;
+        }
+      } else {
+        Queue.push(t, look_ahead);
+        return a;
+      }
+    };
+  };
+  let parse_t = function () {
+    return parse_f_aux(parse_f());
+  };
+  let r = parse_t_aux(parse_t());
   return [
     r,
     Queue.fold((function (acc, x) {
diff --git a/jscomp/test/string_runtime_test.js b/jscomp/test/string_runtime_test.js
index e875088074..f63935b895 100644
--- a/jscomp/test/string_runtime_test.js
+++ b/jscomp/test/string_runtime_test.js
@@ -4,7 +4,6 @@
 let Mt = require("./mt.js");
 let List = require("../../lib/js/list.js");
 let Bytes = require("../../lib/js/bytes.js");
-let $$String = require("../../lib/js/string.js");
 let Test_char = require("./test_char.js");
 let Caml_bytes = require("../../lib/js/caml_bytes.js");
 
@@ -28,9 +27,9 @@ let suites_1 = {
         Bytes.fill(b, 0, x, /* 'c' */99);
         return [
           Bytes.to_string(b),
-          $$String.init(x, (function (param) {
+          Bytes.unsafe_to_string(Bytes.init(x, (function (param) {
             return /* 'c' */99;
-          }))
+          })))
         ];
       }), {
         hd: 1000,
diff --git a/jscomp/test/string_set.js b/jscomp/test/string_set.js
index 985bc64571..7103bdbfba 100644
--- a/jscomp/test/string_set.js
+++ b/jscomp/test/string_set.js
@@ -165,7 +165,7 @@ function compare(s1, s2) {
 }
 
 function equal(s1, s2) {
-  return compare(s1, s2) === 0;
+  return Set_gen.compare($$String.compare, s1, s2) === 0;
 }
 
 function subset(_s1, _s2) {
diff --git a/jscomp/test/string_test.js b/jscomp/test/string_test.js
index b26b614d53..23f7e57812 100644
--- a/jscomp/test/string_test.js
+++ b/jscomp/test/string_test.js
@@ -3,6 +3,7 @@
 
 let Mt = require("./mt.js");
 let List = require("../../lib/js/list.js");
+let $$Array = require("../../lib/js/array.js");
 let Bytes = require("../../lib/js/bytes.js");
 let $$String = require("../../lib/js/string.js");
 let Ext_string_test = require("./ext_string_test.js");
@@ -126,10 +127,10 @@ function xsplit(delim, s) {
 }
 
 function string_of_chars(x) {
-  let extra = List.map((function (prim) {
+  let xs = List.map((function (prim) {
     return String.fromCharCode(prim);
   }), x);
-  return $$String.concat("", extra);
+  return $$Array.of_list(xs).join("");
 }
 
 Mt.from_pair_suites("String_test", {
diff --git a/jscomp/test/test_array_primitive.js b/jscomp/test/test_array_primitive.js
index 69819d9239..d1dc53858d 100644
--- a/jscomp/test/test_array_primitive.js
+++ b/jscomp/test/test_array_primitive.js
@@ -12,27 +12,27 @@ function caml_array_sub(x, offset, len) {
 }
 
 function caml_array_set(xs, index, newval) {
-  if (!(index < 0 || index >= xs.length)) {
-    return Caml_array.set(xs, index, newval);
+  if (index < 0 || index >= xs.length) {
+    throw new Error("Invalid_argument", {
+          cause: {
+            RE_EXN_ID: "Invalid_argument",
+            _1: "index out of bounds"
+          }
+        });
   }
-  throw new Error("Invalid_argument", {
-        cause: {
-          RE_EXN_ID: "Invalid_argument",
-          _1: "index out of bounds"
-        }
-      });
+  Caml_array.set(xs, index, newval);
 }
 
 function caml_array_get(xs, index) {
-  if (!(index < 0 || index >= xs.length)) {
-    return Caml_array.get(xs, index);
+  if (index < 0 || index >= xs.length) {
+    throw new Error("Invalid_argument", {
+          cause: {
+            RE_EXN_ID: "Invalid_argument",
+            _1: "index out of bounds"
+          }
+        });
   }
-  throw new Error("Invalid_argument", {
-        cause: {
-          RE_EXN_ID: "Invalid_argument",
-          _1: "index out of bounds"
-        }
-      });
+  return Caml_array.get(xs, index);
 }
 
 function caml_make_vect(len, init) {
diff --git a/jscomp/test/test_bytes.js b/jscomp/test/test_bytes.js
index b48ab6d8c8..9d625d0f65 100644
--- a/jscomp/test/test_bytes.js
+++ b/jscomp/test/test_bytes.js
@@ -3,9 +3,7 @@
 
 let Bytes = require("../../lib/js/bytes.js");
 
-function f(v) {
-  return Bytes.unsafe_to_string(v);
-}
+let f = Bytes.unsafe_to_string;
 
 let ff = Bytes.to_string;
 
diff --git a/jscomp/test/test_demo.js b/jscomp/test/test_demo.js
index 0724edaa9a..4a5a6409e0 100644
--- a/jscomp/test/test_demo.js
+++ b/jscomp/test/test_demo.js
@@ -59,14 +59,11 @@ function g1(x, y) {
 
 let u = 8;
 
-let x = (function (z) {
-  return u + z | 0;
-})(6);
+let x = u + 6 | 0;
 
 function v(extra) {
   let u = 7;
-  let xx = 6;
-  return (xx + extra | 0) + u | 0;
+  return (6 + extra | 0) + u | 0;
 }
 
 let nil = "Nil";
@@ -84,4 +81,4 @@ exports.g = g;
 exports.g1 = g1;
 exports.x = x;
 exports.v = v;
-/* x Not a pure module */
+/* No side effect */
diff --git a/jscomp/test/test_google_closure.js b/jscomp/test/test_google_closure.js
index 4867382b5a..521a669292 100644
--- a/jscomp/test/test_google_closure.js
+++ b/jscomp/test/test_google_closure.js
@@ -27,7 +27,9 @@ let arr = $$Array.init(2, (function (param) {
 }));
 
 for(let i = 0; i <= 1; ++i){
-  let f3$1 = f2(i);
+  let f3$1 = function (extra) {
+    return i + 1 | 0;
+  };
   Caml_array.set(arr, i, f3$1(2));
 }
 
diff --git a/jscomp/test/test_list.js b/jscomp/test/test_list.js
index 36532409f3..564d252d74 100644
--- a/jscomp/test/test_list.js
+++ b/jscomp/test/test_list.js
@@ -250,15 +250,15 @@ function rev_map2(f, l1, l2) {
             }
           });
     }
-    if (!l2$1) {
-      return accu;
+    if (l2$1) {
+      throw new Error("Invalid_argument", {
+            cause: {
+              RE_EXN_ID: "Invalid_argument",
+              _1: "List.rev_map2"
+            }
+          });
     }
-    throw new Error("Invalid_argument", {
-          cause: {
-            RE_EXN_ID: "Invalid_argument",
-            _1: "List.rev_map2"
-          }
-        });
+    return accu;
   };
 }
 
@@ -311,15 +311,15 @@ function fold_left2(f, _accu, _l1, _l2) {
             }
           });
     }
-    if (!l2) {
-      return accu;
+    if (l2) {
+      throw new Error("Invalid_argument", {
+            cause: {
+              RE_EXN_ID: "Invalid_argument",
+              _1: "List.fold_left2"
+            }
+          });
     }
-    throw new Error("Invalid_argument", {
-          cause: {
-            RE_EXN_ID: "Invalid_argument",
-            _1: "List.fold_left2"
-          }
-        });
+    return accu;
   };
 }
 
@@ -335,15 +335,15 @@ function fold_right2(f, l1, l2, accu) {
           }
         });
   }
-  if (!l2) {
-    return accu;
+  if (l2) {
+    throw new Error("Invalid_argument", {
+          cause: {
+            RE_EXN_ID: "Invalid_argument",
+            _1: "List.fold_right2"
+          }
+        });
   }
-  throw new Error("Invalid_argument", {
-        cause: {
-          RE_EXN_ID: "Invalid_argument",
-          _1: "List.fold_right2"
-        }
-      });
+  return accu;
 }
 
 function for_all(p, _x) {
diff --git a/jscomp/test/test_unsupported_primitive.js b/jscomp/test/test_unsupported_primitive.js
index 9de4f418a1..ac85e30558 100644
--- a/jscomp/test/test_unsupported_primitive.js
+++ b/jscomp/test/test_unsupported_primitive.js
@@ -4,15 +4,15 @@
 let Caml_external_polyfill = require("../../lib/js/caml_external_polyfill.js");
 
 function to_buffer(buff, ofs, len, v, flags) {
-  if (!(ofs < 0 || len < 0 || ofs > (buff.length - len | 0))) {
-    return Caml_external_polyfill.resolve("caml_output_value_to_buffer")(buff, ofs, len, v, flags);
+  if (ofs < 0 || len < 0 || ofs > (buff.length - len | 0)) {
+    throw new Error("Invalid_argument", {
+          cause: {
+            RE_EXN_ID: "Invalid_argument",
+            _1: "Marshal.to_buffer: substring out of bounds"
+          }
+        });
   }
-  throw new Error("Invalid_argument", {
-        cause: {
-          RE_EXN_ID: "Invalid_argument",
-          _1: "Marshal.to_buffer: substring out of bounds"
-        }
-      });
+  return Caml_external_polyfill.resolve("caml_output_value_to_buffer")(buff, ofs, len, v, flags);
 }
 
 exports.to_buffer = to_buffer;
diff --git a/jscomp/test/ticker.js b/jscomp/test/ticker.js
index 80e119537a..c785f5687c 100644
--- a/jscomp/test/ticker.js
+++ b/jscomp/test/ticker.js
@@ -1293,21 +1293,21 @@ function process_input_line(ticker_map, all_tickers, line) {
                     if (match$4) {
                       let match$5 = match$4.tl;
                       if (match$5) {
-                        if (!match$5.tl) {
-                          return [
-                            {
-                              hd: make_binary_op(ticker_name, match$4.hd, match$5.hd, "PLUS"),
-                              tl: all_tickers
-                            },
-                            ticker_map
-                          ];
+                        if (match$5.tl) {
+                          throw new Error("Failure", {
+                                cause: {
+                                  RE_EXN_ID: "Failure",
+                                  _1: "Invalid input line"
+                                }
+                              });
                         }
-                        throw new Error("Failure", {
-                              cause: {
-                                RE_EXN_ID: "Failure",
-                                _1: "Invalid input line"
-                              }
-                            });
+                        return [
+                          {
+                            hd: make_binary_op(ticker_name, match$4.hd, match$5.hd, "PLUS"),
+                            tl: all_tickers
+                          },
+                          ticker_map
+                        ];
                       }
                       throw new Error("Failure", {
                             cause: {
@@ -1327,21 +1327,21 @@ function process_input_line(ticker_map, all_tickers, line) {
                     if (match$6) {
                       let match$7 = match$6.tl;
                       if (match$7) {
-                        if (!match$7.tl) {
-                          return [
-                            {
-                              hd: make_binary_op(ticker_name, match$6.hd, match$7.hd, "MINUS"),
-                              tl: all_tickers
-                            },
-                            ticker_map
-                          ];
+                        if (match$7.tl) {
+                          throw new Error("Failure", {
+                                cause: {
+                                  RE_EXN_ID: "Failure",
+                                  _1: "Invalid input line"
+                                }
+                              });
                         }
-                        throw new Error("Failure", {
-                              cause: {
-                                RE_EXN_ID: "Failure",
-                                _1: "Invalid input line"
-                              }
-                            });
+                        return [
+                          {
+                            hd: make_binary_op(ticker_name, match$6.hd, match$7.hd, "MINUS"),
+                            tl: all_tickers
+                          },
+                          ticker_map
+                        ];
                       }
                       throw new Error("Failure", {
                             cause: {
@@ -1357,26 +1357,26 @@ function process_input_line(ticker_map, all_tickers, line) {
                           }
                         });
                 case "S" :
-                    if (!match$3.tl) {
-                      return [
-                        {
-                          hd: {
-                            value: undefined,
-                            rank: "Uninitialized",
-                            ticker_name: ticker_name,
-                            type_: "Market"
-                          },
-                          tl: all_tickers
-                        },
-                        ticker_map
-                      ];
+                    if (match$3.tl) {
+                      throw new Error("Failure", {
+                            cause: {
+                              RE_EXN_ID: "Failure",
+                              _1: "Invalid input line"
+                            }
+                          });
                     }
-                    throw new Error("Failure", {
-                          cause: {
-                            RE_EXN_ID: "Failure",
-                            _1: "Invalid input line"
-                          }
-                        });
+                    return [
+                      {
+                        hd: {
+                          value: undefined,
+                          rank: "Uninitialized",
+                          ticker_name: ticker_name,
+                          type_: "Market"
+                        },
+                        tl: all_tickers
+                      },
+                      ticker_map
+                    ];
                 default:
                   throw new Error("Failure", {
                         cause: {
diff --git a/jscomp/test/to_string_test.js b/jscomp/test/to_string_test.js
index 58bf0132ca..1e2099db17 100644
--- a/jscomp/test/to_string_test.js
+++ b/jscomp/test/to_string_test.js
@@ -4,9 +4,7 @@
 let Mt = require("./mt.js");
 let Pervasives = require("../../lib/js/pervasives.js");
 
-function ff(v) {
-  return Pervasives.string_of_float(v);
-}
+let ff = Pervasives.string_of_float;
 
 function f(v) {
   return String(v);
diff --git a/jscomp/test/topsort_test.js b/jscomp/test/topsort_test.js
index 8f6ce9ba4a..d9f7b1d719 100644
--- a/jscomp/test/topsort_test.js
+++ b/jscomp/test/topsort_test.js
@@ -409,21 +409,16 @@ function unsafe_topsort(graph) {
   let visited = {
     contents: /* [] */0
   };
-  let sort_nodes = function (nodes) {
-    List.iter((function (node) {
-      sort_node(node);
-    }), nodes);
-  };
   let sort_node = function (node) {
-    if (!List.mem(node, visited.contents)) {
-      sort_nodes(nexts(node, graph));
-      visited.contents = {
-        hd: node,
-        tl: visited.contents
-      };
+    if (List.mem(node, visited.contents)) {
       return;
     }
-    
+    let nodes = nexts(node, graph);
+    List.iter(sort_node, nodes);
+    visited.contents = {
+      hd: node,
+      tl: visited.contents
+    };
   };
   List.iter((function (param) {
     sort_node(param[0]);
diff --git a/jscomp/test/uncurried_cast.js b/jscomp/test/uncurried_cast.js
index 486ea7e6cc..56e3fa54c2 100644
--- a/jscomp/test/uncurried_cast.js
+++ b/jscomp/test/uncurried_cast.js
@@ -10,9 +10,7 @@ function raise(e) {
       });
 }
 
-function map(l, f) {
-  return Belt_List.mapU(l, f);
-}
+let map = Belt_List.mapU;
 
 let List = {
   map: map
diff --git a/lib/es6/array.js b/lib/es6/array.js
index 01edc6755a..c027a50579 100644
--- a/lib/es6/array.js
+++ b/lib/es6/array.js
@@ -57,15 +57,15 @@ function append(a1, a2) {
 }
 
 function sub(a, ofs, len) {
-  if (!(ofs < 0 || len < 0 || ofs > (a.length - len | 0))) {
-    return Caml_array.sub(a, ofs, len);
+  if (ofs < 0 || len < 0 || ofs > (a.length - len | 0)) {
+    throw new Error("Invalid_argument", {
+          cause: {
+            RE_EXN_ID: "Invalid_argument",
+            _1: "Array.sub"
+          }
+        });
   }
-  throw new Error("Invalid_argument", {
-        cause: {
-          RE_EXN_ID: "Invalid_argument",
-          _1: "Array.sub"
-        }
-      });
+  return Caml_array.sub(a, ofs, len);
 }
 
 function fill(a, ofs, len, v) {
@@ -83,15 +83,15 @@ function fill(a, ofs, len, v) {
 }
 
 function blit(a1, ofs1, a2, ofs2, len) {
-  if (!(len < 0 || ofs1 < 0 || ofs1 > (a1.length - len | 0) || ofs2 < 0 || ofs2 > (a2.length - len | 0))) {
-    return Caml_array.blit(a1, ofs1, a2, ofs2, len);
+  if (len < 0 || ofs1 < 0 || ofs1 > (a1.length - len | 0) || ofs2 < 0 || ofs2 > (a2.length - len | 0)) {
+    throw new Error("Invalid_argument", {
+          cause: {
+            RE_EXN_ID: "Invalid_argument",
+            _1: "Array.blit"
+          }
+        });
   }
-  throw new Error("Invalid_argument", {
-        cause: {
-          RE_EXN_ID: "Invalid_argument",
-          _1: "Array.blit"
-        }
-      });
+  Caml_array.blit(a1, ofs1, a2, ofs2, len);
 }
 
 function iter(f, a) {
diff --git a/lib/es6/arrayLabels.js b/lib/es6/arrayLabels.js
index a0d1264e04..cf122ba8dd 100644
--- a/lib/es6/arrayLabels.js
+++ b/lib/es6/arrayLabels.js
@@ -57,15 +57,15 @@ function append(a1, a2) {
 }
 
 function sub(a, ofs, len) {
-  if (!(ofs < 0 || len < 0 || ofs > (a.length - len | 0))) {
-    return Caml_array.sub(a, ofs, len);
+  if (ofs < 0 || len < 0 || ofs > (a.length - len | 0)) {
+    throw new Error("Invalid_argument", {
+          cause: {
+            RE_EXN_ID: "Invalid_argument",
+            _1: "Array.sub"
+          }
+        });
   }
-  throw new Error("Invalid_argument", {
-        cause: {
-          RE_EXN_ID: "Invalid_argument",
-          _1: "Array.sub"
-        }
-      });
+  return Caml_array.sub(a, ofs, len);
 }
 
 function fill(a, ofs, len, v) {
@@ -83,15 +83,15 @@ function fill(a, ofs, len, v) {
 }
 
 function blit(a1, ofs1, a2, ofs2, len) {
-  if (!(len < 0 || ofs1 < 0 || ofs1 > (a1.length - len | 0) || ofs2 < 0 || ofs2 > (a2.length - len | 0))) {
-    return Caml_array.blit(a1, ofs1, a2, ofs2, len);
+  if (len < 0 || ofs1 < 0 || ofs1 > (a1.length - len | 0) || ofs2 < 0 || ofs2 > (a2.length - len | 0)) {
+    throw new Error("Invalid_argument", {
+          cause: {
+            RE_EXN_ID: "Invalid_argument",
+            _1: "Array.blit"
+          }
+        });
   }
-  throw new Error("Invalid_argument", {
-        cause: {
-          RE_EXN_ID: "Invalid_argument",
-          _1: "Array.blit"
-        }
-      });
+  Caml_array.blit(a1, ofs1, a2, ofs2, len);
 }
 
 function iter(f, a) {
diff --git a/lib/es6/belt_Array.js b/lib/es6/belt_Array.js
index 8a0069be35..ddfd231929 100644
--- a/lib/es6/belt_Array.js
+++ b/lib/es6/belt_Array.js
@@ -325,9 +325,9 @@ function flatMapU(a, f) {
 }
 
 function flatMap(a, f) {
-  return flatMapU(a, (function (a) {
+  return concatMany(mapU(a, (function (a) {
     return f(a);
-  }));
+  })));
 }
 
 function getByU(a, p) {
diff --git a/lib/es6/belt_HashMapInt.js b/lib/es6/belt_HashMapInt.js
index 905f88bcd7..2d1d6c8537 100644
--- a/lib/es6/belt_HashMapInt.js
+++ b/lib/es6/belt_HashMapInt.js
@@ -193,7 +193,7 @@ function size(h) {
 
 function fromArray(arr) {
   let len = arr.length;
-  let v = make(len);
+  let v = Belt_internalBucketsType.make(undefined, undefined, len);
   for(let i = 0; i < len; ++i){
     let match = arr[i];
     set(v, match[0], match[1]);
diff --git a/lib/es6/belt_HashMapString.js b/lib/es6/belt_HashMapString.js
index 041b2e8ace..c4352164cb 100644
--- a/lib/es6/belt_HashMapString.js
+++ b/lib/es6/belt_HashMapString.js
@@ -193,7 +193,7 @@ function size(h) {
 
 function fromArray(arr) {
   let len = arr.length;
-  let v = make(len);
+  let v = Belt_internalBucketsType.make(undefined, undefined, len);
   for(let i = 0; i < len; ++i){
     let match = arr[i];
     set(v, match[0], match[1]);
diff --git a/lib/es6/belt_Map.js b/lib/es6/belt_Map.js
index 9c811ba7fe..095b87f0a7 100644
--- a/lib/es6/belt_Map.js
+++ b/lib/es6/belt_Map.js
@@ -112,7 +112,7 @@ function findFirstByU(m, f) {
 }
 
 function findFirstBy(m, f) {
-  return findFirstByU(m, (function (a, b) {
+  return Belt_MapDict.findFirstByU(m.data, (function (a, b) {
     return f(a, b);
   }));
 }
@@ -122,7 +122,7 @@ function forEachU(m, f) {
 }
 
 function forEach(m, f) {
-  forEachU(m, (function (a, b) {
+  Belt_MapDict.forEachU(m.data, (function (a, b) {
     f(a, b);
   }));
 }
@@ -142,7 +142,7 @@ function everyU(m, f) {
 }
 
 function every(m, f) {
-  return everyU(m, (function (a, b) {
+  return Belt_MapDict.everyU(m.data, (function (a, b) {
     return f(a, b);
   }));
 }
@@ -152,7 +152,7 @@ function someU(m, f) {
 }
 
 function some(m, f) {
-  return someU(m, (function (a, b) {
+  return Belt_MapDict.someU(m.data, (function (a, b) {
     return f(a, b);
   }));
 }
diff --git a/lib/es6/belt_MutableMap.js b/lib/es6/belt_MutableMap.js
index df575d99d5..009ef39219 100644
--- a/lib/es6/belt_MutableMap.js
+++ b/lib/es6/belt_MutableMap.js
@@ -153,7 +153,8 @@ function clear(m) {
 }
 
 function isEmpty(d) {
-  return d.data === undefined;
+  let x = d.data;
+  return x === undefined;
 }
 
 function minKey(m) {
@@ -193,7 +194,7 @@ function forEachU(d, f) {
 }
 
 function forEach(d, f) {
-  forEachU(d, (function (a, b) {
+  Belt_internalAVLtree.forEachU(d.data, (function (a, b) {
     f(a, b);
   }));
 }
@@ -213,7 +214,7 @@ function everyU(d, p) {
 }
 
 function every(d, p) {
-  return everyU(d, (function (a, b) {
+  return Belt_internalAVLtree.everyU(d.data, (function (a, b) {
     return p(a, b);
   }));
 }
@@ -223,7 +224,7 @@ function someU(d, p) {
 }
 
 function some(d, p) {
-  return someU(d, (function (a, b) {
+  return Belt_internalAVLtree.someU(d.data, (function (a, b) {
     return p(a, b);
   }));
 }
diff --git a/lib/es6/belt_MutableMapInt.js b/lib/es6/belt_MutableMapInt.js
index dc792430ed..f1549c8441 100644
--- a/lib/es6/belt_MutableMapInt.js
+++ b/lib/es6/belt_MutableMapInt.js
@@ -11,7 +11,8 @@ function make() {
 }
 
 function isEmpty(m) {
-  return m.data === undefined;
+  let x = m.data;
+  return x === undefined;
 }
 
 function clear(m) {
@@ -65,7 +66,7 @@ function forEachU(d, f) {
 }
 
 function forEach(d, f) {
-  forEachU(d, (function (a, b) {
+  Belt_internalAVLtree.forEachU(d.data, (function (a, b) {
     f(a, b);
   }));
 }
@@ -109,7 +110,7 @@ function everyU(d, f) {
 }
 
 function every(d, f) {
-  return everyU(d, (function (a, b) {
+  return Belt_internalAVLtree.everyU(d.data, (function (a, b) {
     return f(a, b);
   }));
 }
@@ -119,7 +120,7 @@ function someU(d, f) {
 }
 
 function some(d, f) {
-  return someU(d, (function (a, b) {
+  return Belt_internalAVLtree.someU(d.data, (function (a, b) {
     return f(a, b);
   }));
 }
diff --git a/lib/es6/belt_MutableMapString.js b/lib/es6/belt_MutableMapString.js
index b0d77bb7e7..60243c3480 100644
--- a/lib/es6/belt_MutableMapString.js
+++ b/lib/es6/belt_MutableMapString.js
@@ -11,7 +11,8 @@ function make() {
 }
 
 function isEmpty(m) {
-  return m.data === undefined;
+  let x = m.data;
+  return x === undefined;
 }
 
 function clear(m) {
@@ -65,7 +66,7 @@ function forEachU(d, f) {
 }
 
 function forEach(d, f) {
-  forEachU(d, (function (a, b) {
+  Belt_internalAVLtree.forEachU(d.data, (function (a, b) {
     f(a, b);
   }));
 }
@@ -109,7 +110,7 @@ function everyU(d, f) {
 }
 
 function every(d, f) {
-  return everyU(d, (function (a, b) {
+  return Belt_internalAVLtree.everyU(d.data, (function (a, b) {
     return f(a, b);
   }));
 }
@@ -119,7 +120,7 @@ function someU(d, f) {
 }
 
 function some(d, f) {
-  return someU(d, (function (a, b) {
+  return Belt_internalAVLtree.someU(d.data, (function (a, b) {
     return f(a, b);
   }));
 }
diff --git a/lib/es6/belt_MutableSet.js b/lib/es6/belt_MutableSet.js
index 05ed011852..49ca11d976 100644
--- a/lib/es6/belt_MutableSet.js
+++ b/lib/es6/belt_MutableSet.js
@@ -192,7 +192,8 @@ function make(id) {
 }
 
 function isEmpty(d) {
-  return d.data === undefined;
+  let n = d.data;
+  return n === undefined;
 }
 
 function minimum(d) {
@@ -216,7 +217,7 @@ function forEachU(d, f) {
 }
 
 function forEach(d, f) {
-  forEachU(d, (function (a) {
+  Belt_internalAVLset.forEachU(d.data, (function (a) {
     f(a);
   }));
 }
@@ -236,7 +237,7 @@ function everyU(d, p) {
 }
 
 function every(d, p) {
-  return everyU(d, (function (a) {
+  return Belt_internalAVLset.everyU(d.data, (function (a) {
     return p(a);
   }));
 }
@@ -246,7 +247,7 @@ function someU(d, p) {
 }
 
 function some(d, p) {
-  return someU(d, (function (a) {
+  return Belt_internalAVLset.someU(d.data, (function (a) {
     return p(a);
   }));
 }
diff --git a/lib/es6/belt_MutableSetInt.js b/lib/es6/belt_MutableSetInt.js
index 47ff473614..1507932c69 100644
--- a/lib/es6/belt_MutableSetInt.js
+++ b/lib/es6/belt_MutableSetInt.js
@@ -189,7 +189,8 @@ function make() {
 }
 
 function isEmpty(d) {
-  return d.data === undefined;
+  let n = d.data;
+  return n === undefined;
 }
 
 function minimum(d) {
@@ -213,7 +214,7 @@ function forEachU(d, f) {
 }
 
 function forEach(d, f) {
-  forEachU(d, (function (a) {
+  Belt_internalAVLset.forEachU(d.data, (function (a) {
     f(a);
   }));
 }
@@ -233,7 +234,7 @@ function everyU(d, p) {
 }
 
 function every(d, p) {
-  return everyU(d, (function (a) {
+  return Belt_internalAVLset.everyU(d.data, (function (a) {
     return p(a);
   }));
 }
@@ -243,7 +244,7 @@ function someU(d, p) {
 }
 
 function some(d, p) {
-  return someU(d, (function (a) {
+  return Belt_internalAVLset.someU(d.data, (function (a) {
     return p(a);
   }));
 }
diff --git a/lib/es6/belt_MutableSetString.js b/lib/es6/belt_MutableSetString.js
index d8a217d1ef..004803ecb6 100644
--- a/lib/es6/belt_MutableSetString.js
+++ b/lib/es6/belt_MutableSetString.js
@@ -189,7 +189,8 @@ function make() {
 }
 
 function isEmpty(d) {
-  return d.data === undefined;
+  let n = d.data;
+  return n === undefined;
 }
 
 function minimum(d) {
@@ -213,7 +214,7 @@ function forEachU(d, f) {
 }
 
 function forEach(d, f) {
-  forEachU(d, (function (a) {
+  Belt_internalAVLset.forEachU(d.data, (function (a) {
     f(a);
   }));
 }
@@ -233,7 +234,7 @@ function everyU(d, p) {
 }
 
 function every(d, p) {
-  return everyU(d, (function (a) {
+  return Belt_internalAVLset.everyU(d.data, (function (a) {
     return p(a);
   }));
 }
@@ -243,7 +244,7 @@ function someU(d, p) {
 }
 
 function some(d, p) {
-  return someU(d, (function (a) {
+  return Belt_internalAVLset.someU(d.data, (function (a) {
     return p(a);
   }));
 }
diff --git a/lib/es6/belt_Set.js b/lib/es6/belt_Set.js
index c68c9f5b85..e2046a6ac2 100644
--- a/lib/es6/belt_Set.js
+++ b/lib/es6/belt_Set.js
@@ -127,7 +127,7 @@ function forEachU(m, f) {
 }
 
 function forEach(m, f) {
-  forEachU(m, (function (a) {
+  Belt_SetDict.forEachU(m.data, (function (a) {
     f(a);
   }));
 }
@@ -147,7 +147,7 @@ function everyU(m, f) {
 }
 
 function every(m, f) {
-  return everyU(m, (function (a) {
+  return Belt_SetDict.everyU(m.data, (function (a) {
     return f(a);
   }));
 }
@@ -157,7 +157,7 @@ function someU(m, f) {
 }
 
 function some(m, f) {
-  return someU(m, (function (a) {
+  return Belt_SetDict.someU(m.data, (function (a) {
     return f(a);
   }));
 }
diff --git a/lib/es6/belt_internalBuckets.js b/lib/es6/belt_internalBuckets.js
index 43299a9adc..7842375964 100644
--- a/lib/es6/belt_internalBuckets.js
+++ b/lib/es6/belt_internalBuckets.js
@@ -3,19 +3,6 @@
 import * as Belt_Array from "./belt_Array.js";
 import * as Caml_option from "./caml_option.js";
 
-function copyBucket(c) {
-  if (c === undefined) {
-    return c;
-  }
-  let head = {
-    key: c.key,
-    value: c.value,
-    next: undefined
-  };
-  copyAuxCont(c.next, head);
-  return head;
-}
-
 function copyAuxCont(_c, _prec) {
   while(true) {
     let prec = _prec;
@@ -35,6 +22,19 @@ function copyAuxCont(_c, _prec) {
   };
 }
 
+function copyBucket(c) {
+  if (c === undefined) {
+    return c;
+  }
+  let head = {
+    key: c.key,
+    value: c.value,
+    next: undefined
+  };
+  copyAuxCont(c.next, head);
+  return head;
+}
+
 function copyBuckets(buckets) {
   let len = buckets.length;
   let newBuckets = new Array(len);
diff --git a/lib/es6/buffer.js b/lib/es6/buffer.js
index 5a3d7c2b44..a396c734a2 100644
--- a/lib/es6/buffer.js
+++ b/lib/es6/buffer.js
@@ -25,39 +25,39 @@ function to_bytes(b) {
 }
 
 function sub(b, ofs, len) {
-  if (!(ofs < 0 || len < 0 || ofs > (b.position - len | 0))) {
-    return Bytes.sub_string(b.buffer, ofs, len);
+  if (ofs < 0 || len < 0 || ofs > (b.position - len | 0)) {
+    throw new Error("Invalid_argument", {
+          cause: {
+            RE_EXN_ID: "Invalid_argument",
+            _1: "Buffer.sub"
+          }
+        });
   }
-  throw new Error("Invalid_argument", {
-        cause: {
-          RE_EXN_ID: "Invalid_argument",
-          _1: "Buffer.sub"
-        }
-      });
+  return Bytes.sub_string(b.buffer, ofs, len);
 }
 
 function blit(src, srcoff, dst, dstoff, len) {
-  if (!(len < 0 || srcoff < 0 || srcoff > (src.position - len | 0) || dstoff < 0 || dstoff > (dst.length - len | 0))) {
-    return Bytes.blit(src.buffer, srcoff, dst, dstoff, len);
+  if (len < 0 || srcoff < 0 || srcoff > (src.position - len | 0) || dstoff < 0 || dstoff > (dst.length - len | 0)) {
+    throw new Error("Invalid_argument", {
+          cause: {
+            RE_EXN_ID: "Invalid_argument",
+            _1: "Buffer.blit"
+          }
+        });
   }
-  throw new Error("Invalid_argument", {
-        cause: {
-          RE_EXN_ID: "Invalid_argument",
-          _1: "Buffer.blit"
-        }
-      });
+  Bytes.blit(src.buffer, srcoff, dst, dstoff, len);
 }
 
 function nth(b, ofs) {
-  if (!(ofs < 0 || ofs >= b.position)) {
-    return b.buffer[ofs];
+  if (ofs < 0 || ofs >= b.position) {
+    throw new Error("Invalid_argument", {
+          cause: {
+            RE_EXN_ID: "Invalid_argument",
+            _1: "Buffer.nth"
+          }
+        });
   }
-  throw new Error("Invalid_argument", {
-        cause: {
-          RE_EXN_ID: "Invalid_argument",
-          _1: "Buffer.nth"
-        }
-      });
+  return b.buffer[ofs];
 }
 
 function length(b) {
@@ -454,16 +454,15 @@ function add_substitute(b, f, s) {
 }
 
 function truncate(b, len) {
-  if (!(len < 0 || len > b.position)) {
-    b.position = len;
-    return;
+  if (len < 0 || len > b.position) {
+    throw new Error("Invalid_argument", {
+          cause: {
+            RE_EXN_ID: "Invalid_argument",
+            _1: "Buffer.truncate"
+          }
+        });
   }
-  throw new Error("Invalid_argument", {
-        cause: {
-          RE_EXN_ID: "Invalid_argument",
-          _1: "Buffer.truncate"
-        }
-      });
+  b.position = len;
 }
 
 export {
diff --git a/lib/es6/bytes.js b/lib/es6/bytes.js
index c0ae45e111..39bf696da3 100644
--- a/lib/es6/bytes.js
+++ b/lib/es6/bytes.js
@@ -148,15 +148,15 @@ function $plus$plus(a, b) {
   if (match$1) {
     return c;
   }
-  if (!match$2) {
-    return c;
+  if (match$2) {
+    throw new Error("Invalid_argument", {
+          cause: {
+            RE_EXN_ID: "Invalid_argument",
+            _1: "Bytes.extend"
+          }
+        });
   }
-  throw new Error("Invalid_argument", {
-        cause: {
-          RE_EXN_ID: "Invalid_argument",
-          _1: "Bytes.extend"
-        }
-      });
+  return c;
 }
 
 function extend(s, left, right) {
@@ -179,55 +179,54 @@ function extend(s, left, right) {
 }
 
 function fill(s, ofs, len, c) {
-  if (!(ofs < 0 || len < 0 || ofs > (s.length - len | 0))) {
-    return unsafe_fill(s, ofs, len, c);
+  if (ofs < 0 || len < 0 || ofs > (s.length - len | 0)) {
+    throw new Error("Invalid_argument", {
+          cause: {
+            RE_EXN_ID: "Invalid_argument",
+            _1: "String.fill / Bytes.fill"
+          }
+        });
   }
-  throw new Error("Invalid_argument", {
-        cause: {
-          RE_EXN_ID: "Invalid_argument",
-          _1: "String.fill / Bytes.fill"
-        }
-      });
+  unsafe_fill(s, ofs, len, c);
 }
 
 function blit(s1, ofs1, s2, ofs2, len) {
-  if (!(len < 0 || ofs1 < 0 || ofs1 > (s1.length - len | 0) || ofs2 < 0 || ofs2 > (s2.length - len | 0))) {
-    return unsafe_blit(s1, ofs1, s2, ofs2, len);
+  if (len < 0 || ofs1 < 0 || ofs1 > (s1.length - len | 0) || ofs2 < 0 || ofs2 > (s2.length - len | 0)) {
+    throw new Error("Invalid_argument", {
+          cause: {
+            RE_EXN_ID: "Invalid_argument",
+            _1: "Bytes.blit"
+          }
+        });
   }
-  throw new Error("Invalid_argument", {
-        cause: {
-          RE_EXN_ID: "Invalid_argument",
-          _1: "Bytes.blit"
-        }
-      });
+  unsafe_blit(s1, ofs1, s2, ofs2, len);
 }
 
 function blit_string(s1, ofs1, s2, ofs2, len) {
-  if (!(len < 0 || ofs1 < 0 || ofs1 > (s1.length - len | 0) || ofs2 < 0 || ofs2 > (s2.length - len | 0))) {
-    if (len <= 0) {
-      return;
-    }
-    let off1 = s1.length - ofs1 | 0;
-    if (len <= off1) {
-      for(let i = 0; i < len; ++i){
-        s2[ofs2 + i | 0] = s1.codePointAt(ofs1 + i | 0);
-      }
-      return;
-    }
-    for(let i$1 = 0; i$1 < off1; ++i$1){
-      s2[ofs2 + i$1 | 0] = s1.codePointAt(ofs1 + i$1 | 0);
-    }
-    for(let i$2 = off1; i$2 < len; ++i$2){
-      s2[ofs2 + i$2 | 0] = /* '\000' */0;
+  if (len < 0 || ofs1 < 0 || ofs1 > (s1.length - len | 0) || ofs2 < 0 || ofs2 > (s2.length - len | 0)) {
+    throw new Error("Invalid_argument", {
+          cause: {
+            RE_EXN_ID: "Invalid_argument",
+            _1: "String.blit / Bytes.blit_string"
+          }
+        });
+  }
+  if (len <= 0) {
+    return;
+  }
+  let off1 = s1.length - ofs1 | 0;
+  if (len <= off1) {
+    for(let i = 0; i < len; ++i){
+      s2[ofs2 + i | 0] = s1.codePointAt(ofs1 + i | 0);
     }
     return;
   }
-  throw new Error("Invalid_argument", {
-        cause: {
-          RE_EXN_ID: "Invalid_argument",
-          _1: "String.blit / Bytes.blit_string"
-        }
-      });
+  for(let i$1 = 0; i$1 < off1; ++i$1){
+    s2[ofs2 + i$1 | 0] = s1.codePointAt(ofs1 + i$1 | 0);
+  }
+  for(let i$2 = off1; i$2 < len; ++i$2){
+    s2[ofs2 + i$2 | 0] = /* '\000' */0;
+  }
 }
 
 function iter(f, a) {
@@ -530,28 +529,28 @@ function index_opt(s, c) {
 
 function index_from(s, i, c) {
   let l = s.length;
-  if (!(i < 0 || i > l)) {
-    return index_rec(s, l, i, c);
+  if (i < 0 || i > l) {
+    throw new Error("Invalid_argument", {
+          cause: {
+            RE_EXN_ID: "Invalid_argument",
+            _1: "String.index_from / Bytes.index_from"
+          }
+        });
   }
-  throw new Error("Invalid_argument", {
-        cause: {
-          RE_EXN_ID: "Invalid_argument",
-          _1: "String.index_from / Bytes.index_from"
-        }
-      });
+  return index_rec(s, l, i, c);
 }
 
 function index_from_opt(s, i, c) {
   let l = s.length;
-  if (!(i < 0 || i > l)) {
-    return index_rec_opt(s, l, i, c);
+  if (i < 0 || i > l) {
+    throw new Error("Invalid_argument", {
+          cause: {
+            RE_EXN_ID: "Invalid_argument",
+            _1: "String.index_from_opt / Bytes.index_from_opt"
+          }
+        });
   }
-  throw new Error("Invalid_argument", {
-        cause: {
-          RE_EXN_ID: "Invalid_argument",
-          _1: "String.index_from_opt / Bytes.index_from_opt"
-        }
-      });
+  return index_rec_opt(s, l, i, c);
 }
 
 function rindex_rec(s, _i, c) {
@@ -577,15 +576,15 @@ function rindex(s, c) {
 }
 
 function rindex_from(s, i, c) {
-  if (!(i < -1 || i >= s.length)) {
-    return rindex_rec(s, i, c);
+  if (i < -1 || i >= s.length) {
+    throw new Error("Invalid_argument", {
+          cause: {
+            RE_EXN_ID: "Invalid_argument",
+            _1: "String.rindex_from / Bytes.rindex_from"
+          }
+        });
   }
-  throw new Error("Invalid_argument", {
-        cause: {
-          RE_EXN_ID: "Invalid_argument",
-          _1: "String.rindex_from / Bytes.rindex_from"
-        }
-      });
+  return rindex_rec(s, i, c);
 }
 
 function rindex_rec_opt(s, _i, c) {
@@ -607,15 +606,15 @@ function rindex_opt(s, c) {
 }
 
 function rindex_from_opt(s, i, c) {
-  if (!(i < -1 || i >= s.length)) {
-    return rindex_rec_opt(s, i, c);
+  if (i < -1 || i >= s.length) {
+    throw new Error("Invalid_argument", {
+          cause: {
+            RE_EXN_ID: "Invalid_argument",
+            _1: "String.rindex_from_opt / Bytes.rindex_from_opt"
+          }
+        });
   }
-  throw new Error("Invalid_argument", {
-        cause: {
-          RE_EXN_ID: "Invalid_argument",
-          _1: "String.rindex_from_opt / Bytes.rindex_from_opt"
-        }
-      });
+  return rindex_rec_opt(s, i, c);
 }
 
 function contains_from(s, i, c) {
diff --git a/lib/es6/bytesLabels.js b/lib/es6/bytesLabels.js
index c0ae45e111..39bf696da3 100644
--- a/lib/es6/bytesLabels.js
+++ b/lib/es6/bytesLabels.js
@@ -148,15 +148,15 @@ function $plus$plus(a, b) {
   if (match$1) {
     return c;
   }
-  if (!match$2) {
-    return c;
+  if (match$2) {
+    throw new Error("Invalid_argument", {
+          cause: {
+            RE_EXN_ID: "Invalid_argument",
+            _1: "Bytes.extend"
+          }
+        });
   }
-  throw new Error("Invalid_argument", {
-        cause: {
-          RE_EXN_ID: "Invalid_argument",
-          _1: "Bytes.extend"
-        }
-      });
+  return c;
 }
 
 function extend(s, left, right) {
@@ -179,55 +179,54 @@ function extend(s, left, right) {
 }
 
 function fill(s, ofs, len, c) {
-  if (!(ofs < 0 || len < 0 || ofs > (s.length - len | 0))) {
-    return unsafe_fill(s, ofs, len, c);
+  if (ofs < 0 || len < 0 || ofs > (s.length - len | 0)) {
+    throw new Error("Invalid_argument", {
+          cause: {
+            RE_EXN_ID: "Invalid_argument",
+            _1: "String.fill / Bytes.fill"
+          }
+        });
   }
-  throw new Error("Invalid_argument", {
-        cause: {
-          RE_EXN_ID: "Invalid_argument",
-          _1: "String.fill / Bytes.fill"
-        }
-      });
+  unsafe_fill(s, ofs, len, c);
 }
 
 function blit(s1, ofs1, s2, ofs2, len) {
-  if (!(len < 0 || ofs1 < 0 || ofs1 > (s1.length - len | 0) || ofs2 < 0 || ofs2 > (s2.length - len | 0))) {
-    return unsafe_blit(s1, ofs1, s2, ofs2, len);
+  if (len < 0 || ofs1 < 0 || ofs1 > (s1.length - len | 0) || ofs2 < 0 || ofs2 > (s2.length - len | 0)) {
+    throw new Error("Invalid_argument", {
+          cause: {
+            RE_EXN_ID: "Invalid_argument",
+            _1: "Bytes.blit"
+          }
+        });
   }
-  throw new Error("Invalid_argument", {
-        cause: {
-          RE_EXN_ID: "Invalid_argument",
-          _1: "Bytes.blit"
-        }
-      });
+  unsafe_blit(s1, ofs1, s2, ofs2, len);
 }
 
 function blit_string(s1, ofs1, s2, ofs2, len) {
-  if (!(len < 0 || ofs1 < 0 || ofs1 > (s1.length - len | 0) || ofs2 < 0 || ofs2 > (s2.length - len | 0))) {
-    if (len <= 0) {
-      return;
-    }
-    let off1 = s1.length - ofs1 | 0;
-    if (len <= off1) {
-      for(let i = 0; i < len; ++i){
-        s2[ofs2 + i | 0] = s1.codePointAt(ofs1 + i | 0);
-      }
-      return;
-    }
-    for(let i$1 = 0; i$1 < off1; ++i$1){
-      s2[ofs2 + i$1 | 0] = s1.codePointAt(ofs1 + i$1 | 0);
-    }
-    for(let i$2 = off1; i$2 < len; ++i$2){
-      s2[ofs2 + i$2 | 0] = /* '\000' */0;
+  if (len < 0 || ofs1 < 0 || ofs1 > (s1.length - len | 0) || ofs2 < 0 || ofs2 > (s2.length - len | 0)) {
+    throw new Error("Invalid_argument", {
+          cause: {
+            RE_EXN_ID: "Invalid_argument",
+            _1: "String.blit / Bytes.blit_string"
+          }
+        });
+  }
+  if (len <= 0) {
+    return;
+  }
+  let off1 = s1.length - ofs1 | 0;
+  if (len <= off1) {
+    for(let i = 0; i < len; ++i){
+      s2[ofs2 + i | 0] = s1.codePointAt(ofs1 + i | 0);
     }
     return;
   }
-  throw new Error("Invalid_argument", {
-        cause: {
-          RE_EXN_ID: "Invalid_argument",
-          _1: "String.blit / Bytes.blit_string"
-        }
-      });
+  for(let i$1 = 0; i$1 < off1; ++i$1){
+    s2[ofs2 + i$1 | 0] = s1.codePointAt(ofs1 + i$1 | 0);
+  }
+  for(let i$2 = off1; i$2 < len; ++i$2){
+    s2[ofs2 + i$2 | 0] = /* '\000' */0;
+  }
 }
 
 function iter(f, a) {
@@ -530,28 +529,28 @@ function index_opt(s, c) {
 
 function index_from(s, i, c) {
   let l = s.length;
-  if (!(i < 0 || i > l)) {
-    return index_rec(s, l, i, c);
+  if (i < 0 || i > l) {
+    throw new Error("Invalid_argument", {
+          cause: {
+            RE_EXN_ID: "Invalid_argument",
+            _1: "String.index_from / Bytes.index_from"
+          }
+        });
   }
-  throw new Error("Invalid_argument", {
-        cause: {
-          RE_EXN_ID: "Invalid_argument",
-          _1: "String.index_from / Bytes.index_from"
-        }
-      });
+  return index_rec(s, l, i, c);
 }
 
 function index_from_opt(s, i, c) {
   let l = s.length;
-  if (!(i < 0 || i > l)) {
-    return index_rec_opt(s, l, i, c);
+  if (i < 0 || i > l) {
+    throw new Error("Invalid_argument", {
+          cause: {
+            RE_EXN_ID: "Invalid_argument",
+            _1: "String.index_from_opt / Bytes.index_from_opt"
+          }
+        });
   }
-  throw new Error("Invalid_argument", {
-        cause: {
-          RE_EXN_ID: "Invalid_argument",
-          _1: "String.index_from_opt / Bytes.index_from_opt"
-        }
-      });
+  return index_rec_opt(s, l, i, c);
 }
 
 function rindex_rec(s, _i, c) {
@@ -577,15 +576,15 @@ function rindex(s, c) {
 }
 
 function rindex_from(s, i, c) {
-  if (!(i < -1 || i >= s.length)) {
-    return rindex_rec(s, i, c);
+  if (i < -1 || i >= s.length) {
+    throw new Error("Invalid_argument", {
+          cause: {
+            RE_EXN_ID: "Invalid_argument",
+            _1: "String.rindex_from / Bytes.rindex_from"
+          }
+        });
   }
-  throw new Error("Invalid_argument", {
-        cause: {
-          RE_EXN_ID: "Invalid_argument",
-          _1: "String.rindex_from / Bytes.rindex_from"
-        }
-      });
+  return rindex_rec(s, i, c);
 }
 
 function rindex_rec_opt(s, _i, c) {
@@ -607,15 +606,15 @@ function rindex_opt(s, c) {
 }
 
 function rindex_from_opt(s, i, c) {
-  if (!(i < -1 || i >= s.length)) {
-    return rindex_rec_opt(s, i, c);
+  if (i < -1 || i >= s.length) {
+    throw new Error("Invalid_argument", {
+          cause: {
+            RE_EXN_ID: "Invalid_argument",
+            _1: "String.rindex_from_opt / Bytes.rindex_from_opt"
+          }
+        });
   }
-  throw new Error("Invalid_argument", {
-        cause: {
-          RE_EXN_ID: "Invalid_argument",
-          _1: "String.rindex_from_opt / Bytes.rindex_from_opt"
-        }
-      });
+  return rindex_rec_opt(s, i, c);
 }
 
 function contains_from(s, i, c) {
diff --git a/lib/es6/caml.js b/lib/es6/caml.js
index 65242212b2..a85e2555f3 100644
--- a/lib/es6/caml.js
+++ b/lib/es6/caml.js
@@ -166,10 +166,10 @@ function i64_le(x, y) {
 }
 
 function i64_min(x, y) {
-  if (i64_lt(x, y)) {
-    return x;
-  } else {
+  if (i64_ge(x, y)) {
     return y;
+  } else {
+    return x;
   }
 }
 
diff --git a/lib/es6/char.js b/lib/es6/char.js
index 3c49e01262..3e41fcddf6 100644
--- a/lib/es6/char.js
+++ b/lib/es6/char.js
@@ -3,15 +3,15 @@
 import * as Bytes from "./bytes.js";
 
 function chr(n) {
-  if (!(n < 0 || n > 255)) {
-    return n;
+  if (n < 0 || n > 255) {
+    throw new Error("Invalid_argument", {
+          cause: {
+            RE_EXN_ID: "Invalid_argument",
+            _1: "Char.chr"
+          }
+        });
   }
-  throw new Error("Invalid_argument", {
-        cause: {
-          RE_EXN_ID: "Invalid_argument",
-          _1: "Char.chr"
-        }
-      });
+  return n;
 }
 
 function escaped(param) {
diff --git a/lib/es6/digest.js b/lib/es6/digest.js
index 8025c68591..d321133827 100644
--- a/lib/es6/digest.js
+++ b/lib/es6/digest.js
@@ -16,15 +16,15 @@ function bytes(b) {
 }
 
 function substring(str, ofs, len) {
-  if (!(ofs < 0 || len < 0 || ofs > (str.length - len | 0))) {
-    return Caml_md5.md5_string(str, ofs, len);
+  if (ofs < 0 || len < 0 || ofs > (str.length - len | 0)) {
+    throw new Error("Invalid_argument", {
+          cause: {
+            RE_EXN_ID: "Invalid_argument",
+            _1: "Digest.substring"
+          }
+        });
   }
-  throw new Error("Invalid_argument", {
-        cause: {
-          RE_EXN_ID: "Invalid_argument",
-          _1: "Digest.substring"
-        }
-      });
+  return Caml_md5.md5_string(str, ofs, len);
 }
 
 function subbytes(b, ofs, len) {
diff --git a/lib/es6/filename.js b/lib/es6/filename.js
index f894484288..1c278eaa94 100644
--- a/lib/es6/filename.js
+++ b/lib/es6/filename.js
@@ -1,6 +1,7 @@
 
 
 import * as Sys from "./sys.js";
+import * as Bytes from "./bytes.js";
 import * as Buffer from "./buffer.js";
 import * as $$String from "./string.js";
 import * as Caml_sys from "./caml_sys.js";
@@ -193,7 +194,7 @@ function check_suffix$1(name, suff) {
     return false;
   }
   let s = $$String.sub(name, name.length - suff.length | 0, suff.length);
-  return $$String.lowercase_ascii(s) === $$String.lowercase_ascii(suff);
+  return Bytes.unsafe_to_string(Bytes.lowercase_ascii(Bytes.unsafe_of_string(s))) === Bytes.unsafe_to_string(Bytes.lowercase_ascii(Bytes.unsafe_of_string(suff)));
 }
 
 let temp_dir_name$1;
@@ -382,15 +383,15 @@ function concat(dirname, filename) {
 
 function chop_suffix(name, suff) {
   let n = name.length - suff.length | 0;
-  if (n >= 0) {
-    return $$String.sub(name, 0, n);
+  if (n < 0) {
+    throw new Error("Invalid_argument", {
+          cause: {
+            RE_EXN_ID: "Invalid_argument",
+            _1: "Filename.chop_suffix"
+          }
+        });
   }
-  throw new Error("Invalid_argument", {
-        cause: {
-          RE_EXN_ID: "Invalid_argument",
-          _1: "Filename.chop_suffix"
-        }
-      });
+  return $$String.sub(name, 0, n);
 }
 
 function extension_len(name) {
@@ -430,15 +431,15 @@ function extension(name) {
 
 function chop_extension(name) {
   let l = extension_len(name);
-  if (l !== 0) {
-    return $$String.sub(name, 0, name.length - l | 0);
+  if (l === 0) {
+    throw new Error("Invalid_argument", {
+          cause: {
+            RE_EXN_ID: "Invalid_argument",
+            _1: "Filename.chop_extension"
+          }
+        });
   }
-  throw new Error("Invalid_argument", {
-        cause: {
-          RE_EXN_ID: "Invalid_argument",
-          _1: "Filename.chop_extension"
-        }
-      });
+  return $$String.sub(name, 0, name.length - l | 0);
 }
 
 function remove_extension(name) {
diff --git a/lib/es6/genlex.js b/lib/es6/genlex.js
index 5a0b8ed711..db2acdd716 100644
--- a/lib/es6/genlex.js
+++ b/lib/es6/genlex.js
@@ -105,8 +105,8 @@ function make_lexer(keywords) {
               case 13 :
               case 26 :
               case 32 :
-                  exit = 2;
-                  break;
+                  Stream.junk(strm__);
+                  continue;
               case 34 :
                   Stream.junk(strm__);
                   reset_buffer();
@@ -175,10 +175,11 @@ function make_lexer(keywords) {
                     store(/* '-' */45);
                     store(c$2);
                     return number(strm__);
+                  } else {
+                    reset_buffer();
+                    store(/* '-' */45);
+                    return ident2(strm__);
                   }
-                  reset_buffer();
-                  store(/* '-' */45);
-                  return ident2(strm__);
               case 48 :
               case 49 :
               case 50 :
@@ -189,7 +190,7 @@ function make_lexer(keywords) {
               case 55 :
               case 56 :
               case 57 :
-                  exit = 5;
+                  exit = 4;
                   break;
               case 0 :
               case 1 :
@@ -238,7 +239,7 @@ function make_lexer(keywords) {
               case 62 :
               case 63 :
               case 64 :
-                  exit = 4;
+                  exit = 3;
                   break;
               
             }
@@ -247,7 +248,7 @@ function make_lexer(keywords) {
           switch (c) {
             case 92 :
             case 94 :
-                exit = 4;
+                exit = 3;
                 break;
             case 91 :
             case 93 :
@@ -255,14 +256,14 @@ function make_lexer(keywords) {
                 exit = 1;
                 break;
             default:
-              exit = 3;
+              exit = 2;
           }
         }
       } else {
         exit = c >= 127 ? (
-            c > 255 || c < 192 ? 1 : 3
+            c > 255 || c < 192 ? 1 : 2
           ) : (
-            c !== 125 ? 4 : 1
+            c !== 125 ? 3 : 1
           );
       }
       switch (exit) {
@@ -270,49 +271,42 @@ function make_lexer(keywords) {
             Stream.junk(strm__);
             return keyword_or_error(c);
         case 2 :
-            Stream.junk(strm__);
-            continue;
-        case 3 :
             Stream.junk(strm__);
             reset_buffer();
             store(c);
             while(true) {
               let c$3 = Stream.peek(strm__);
-              if (c$3 !== undefined) {
-                let exit$1 = 0;
-                if (c$3 >= 91) {
-                  if (c$3 > 122 || c$3 < 95) {
-                    if (!(c$3 > 255 || c$3 < 192)) {
-                      exit$1 = 2;
-                    }
-                    
-                  } else if (c$3 !== 96) {
-                    exit$1 = 2;
-                  }
-                  
-                } else if (c$3 >= 48) {
-                  if (c$3 > 64 || c$3 < 58) {
-                    exit$1 = 2;
+              if (c$3 === undefined) {
+                return ident_or_keyword(get_string());
+              }
+              if (c$3 >= 91) {
+                if (c$3 > 122 || c$3 < 95) {
+                  if (c$3 > 255 || c$3 < 192) {
+                    return ident_or_keyword(get_string());
                   }
                   
-                } else if (c$3 === 39) {
-                  exit$1 = 2;
+                } else if (c$3 === 96) {
+                  return ident_or_keyword(get_string());
                 }
-                if (exit$1 === 2) {
-                  Stream.junk(strm__);
-                  store(c$3);
-                  continue;
+                
+              } else if (c$3 >= 48) {
+                if (!(c$3 > 64 || c$3 < 58)) {
+                  return ident_or_keyword(get_string());
                 }
                 
+              } else if (c$3 !== 39) {
+                return ident_or_keyword(get_string());
               }
-              return ident_or_keyword(get_string());
+              Stream.junk(strm__);
+              store(c$3);
+              continue;
             };
-        case 4 :
+        case 3 :
             Stream.junk(strm__);
             reset_buffer();
             store(c);
             return ident2(strm__);
-        case 5 :
+        case 4 :
             Stream.junk(strm__);
             reset_buffer();
             store(c);
@@ -324,81 +318,80 @@ function make_lexer(keywords) {
   let ident2 = function (strm__) {
     while(true) {
       let c = Stream.peek(strm__);
-      if (c !== undefined) {
-        let exit = 0;
-        if (c >= 94) {
-          if (c > 125 || c < 95) {
-            if (c < 127) {
-              exit = 2;
-            }
-            
-          } else if (c === 124) {
-            exit = 2;
-          }
-          
-        } else if (c >= 65) {
-          if (c === 92) {
-            exit = 2;
+      if (c === undefined) {
+        return ident_or_keyword(get_string());
+      }
+      if (c >= 94) {
+        if (c > 125 || c < 95) {
+          if (c >= 127) {
+            return ident_or_keyword(get_string());
           }
           
-        } else if (c >= 33) {
-          switch (c) {
-            case 34 :
-            case 39 :
-            case 40 :
-            case 41 :
-            case 44 :
-            case 46 :
-            case 48 :
-            case 49 :
-            case 50 :
-            case 51 :
-            case 52 :
-            case 53 :
-            case 54 :
-            case 55 :
-            case 56 :
-            case 57 :
-            case 59 :
-                break;
-            case 33 :
-            case 35 :
-            case 36 :
-            case 37 :
-            case 38 :
-            case 42 :
-            case 43 :
-            case 45 :
-            case 47 :
-            case 58 :
-            case 60 :
-            case 61 :
-            case 62 :
-            case 63 :
-            case 64 :
-                exit = 2;
-                break;
-            
-          }
+        } else if (c !== 124) {
+          return ident_or_keyword(get_string());
         }
-        if (exit === 2) {
-          Stream.junk(strm__);
-          store(c);
-          continue;
+        
+      } else if (c >= 65) {
+        if (c !== 92) {
+          return ident_or_keyword(get_string());
         }
         
+      } else {
+        if (c < 33) {
+          return ident_or_keyword(get_string());
+        }
+        switch (c) {
+          case 34 :
+          case 39 :
+          case 40 :
+          case 41 :
+          case 44 :
+          case 46 :
+          case 48 :
+          case 49 :
+          case 50 :
+          case 51 :
+          case 52 :
+          case 53 :
+          case 54 :
+          case 55 :
+          case 56 :
+          case 57 :
+          case 59 :
+              return ident_or_keyword(get_string());
+          case 33 :
+          case 35 :
+          case 36 :
+          case 37 :
+          case 38 :
+          case 42 :
+          case 43 :
+          case 45 :
+          case 47 :
+          case 58 :
+          case 60 :
+          case 61 :
+          case 62 :
+          case 63 :
+          case 64 :
+              break;
+          
+        }
       }
-      return ident_or_keyword(get_string());
+      Stream.junk(strm__);
+      store(c);
+      continue;
     };
   };
   let number = function (strm__) {
     while(true) {
       let c = Stream.peek(strm__);
       if (c !== undefined) {
-        let exit = 0;
         if (c >= 58) {
           if (!(c !== 69 && c !== 101)) {
-            exit = 2;
+            Stream.junk(strm__);
+            store(/* 'E' */69);
+            return exponent_part(strm__);
           }
           
         } else if (c !== 46) {
@@ -434,12 +427,6 @@ function make_lexer(keywords) {
             };
           };
         }
-        if (exit === 2) {
-          Stream.junk(strm__);
-          store(/* 'E' */69);
-          return exponent_part(strm__);
-        }
-        
       }
       return {
         TAG: "Int",
@@ -449,15 +436,13 @@ function make_lexer(keywords) {
   };
   let exponent_part = function (strm__) {
     let c = Stream.peek(strm__);
-    if (c === undefined) {
+    if (c !== undefined && !(c !== 43 && c !== 45)) {
+      Stream.junk(strm__);
+      store(c);
       return end_exponent_part(strm__);
-    }
-    if (c !== 43 && c !== 45) {
+    } else {
       return end_exponent_part(strm__);
     }
-    Stream.junk(strm__);
-    store(c);
-    return end_exponent_part(strm__);
   };
   let end_exponent_part = function (strm__) {
     while(true) {
@@ -692,4 +677,4 @@ function make_lexer(keywords) {
 export {
   make_lexer,
 }
-/* Hashtbl Not a pure module */
+/* No side effect */
diff --git a/lib/es6/hashtbl.js b/lib/es6/hashtbl.js
index ca21010481..c0ea9129b9 100644
--- a/lib/es6/hashtbl.js
+++ b/lib/es6/hashtbl.js
@@ -1,7 +1,6 @@
 
 
 import * as Caml from "./caml.js";
-import * as Lazy from "./lazy.js";
 import * as $$Array from "./array.js";
 import * as Random from "./random.js";
 import * as Caml_obj from "./caml_obj.js";
@@ -39,7 +38,7 @@ function is_randomized() {
   return randomized.contents;
 }
 
-let prng = Lazy.from_fun(function () {
+let prng = CamlinternalLazy.from_fun(function () {
   return Random.State.make_self_init();
 });
 
@@ -1142,4 +1141,4 @@ export {
   hash_param,
   seeded_hash_param,
 }
-/* prng Not a pure module */
+/* No side effect */
diff --git a/lib/es6/hashtblLabels.js b/lib/es6/hashtblLabels.js
index 9b3a3844a1..7c623f7274 100644
--- a/lib/es6/hashtblLabels.js
+++ b/lib/es6/hashtblLabels.js
@@ -196,4 +196,4 @@ export {
   MakeSeeded,
   Make,
 }
-/* Hashtbl Not a pure module */
+/* No side effect */
diff --git a/lib/es6/js.js b/lib/es6/js.js
index bc89eac524..59a50d1787 100644
--- a/lib/es6/js.js
+++ b/lib/es6/js.js
@@ -1,8 +1,6 @@
 
 
 
-let Internal = {};
-
 let Null;
 
 let Undefined;
@@ -70,7 +68,6 @@ let $$Map;
 let $$WeakMap;
 
 export {
-  Internal,
   Null,
   Undefined,
   Nullable,
diff --git a/lib/es6/lazy.js b/lib/es6/lazy.js
index 9153ac974b..14e2ebd88b 100644
--- a/lib/es6/lazy.js
+++ b/lib/es6/lazy.js
@@ -8,9 +8,7 @@ function from_fun(f) {
   });
 }
 
-function from_val(v) {
-  return CamlinternalLazy.from_val(v);
-}
+let from_val = CamlinternalLazy.from_val;
 
 let Undefined = CamlinternalLazy.Undefined;
 
diff --git a/lib/es6/list.js b/lib/es6/list.js
index 75645dc081..02a588f97a 100644
--- a/lib/es6/list.js
+++ b/lib/es6/list.js
@@ -155,19 +155,19 @@ function init_aux(i, n, f) {
 }
 
 function init(len, f) {
-  if (len >= 0) {
-    if (len > 10000) {
-      return rev_append(init_tailrec_aux(/* [] */0, 0, len, f), /* [] */0);
-    } else {
-      return init_aux(0, len, f);
-    }
+  if (len < 0) {
+    throw new Error("Invalid_argument", {
+          cause: {
+            RE_EXN_ID: "Invalid_argument",
+            _1: "List.init"
+          }
+        });
+  }
+  if (len > 10000) {
+    return rev_append(init_tailrec_aux(/* [] */0, 0, len, f), /* [] */0);
+  } else {
+    return init_aux(0, len, f);
   }
-  throw new Error("Invalid_argument", {
-        cause: {
-          RE_EXN_ID: "Invalid_argument",
-          _1: "List.init"
-        }
-      });
 }
 
 function flatten(param) {
@@ -323,15 +323,15 @@ function rev_map2(f, l1, l2) {
             }
           });
     }
-    if (!l2$1) {
-      return accu;
+    if (l2$1) {
+      throw new Error("Invalid_argument", {
+            cause: {
+              RE_EXN_ID: "Invalid_argument",
+              _1: "List.rev_map2"
+            }
+          });
     }
-    throw new Error("Invalid_argument", {
-          cause: {
-            RE_EXN_ID: "Invalid_argument",
-            _1: "List.rev_map2"
-          }
-        });
+    return accu;
   };
 }
 
@@ -384,15 +384,15 @@ function fold_left2(f, _accu, _l1, _l2) {
             }
           });
     }
-    if (!l2) {
-      return accu;
+    if (l2) {
+      throw new Error("Invalid_argument", {
+            cause: {
+              RE_EXN_ID: "Invalid_argument",
+              _1: "List.fold_left2"
+            }
+          });
     }
-    throw new Error("Invalid_argument", {
-          cause: {
-            RE_EXN_ID: "Invalid_argument",
-            _1: "List.fold_left2"
-          }
-        });
+    return accu;
   };
 }
 
@@ -408,15 +408,15 @@ function fold_right2(f, l1, l2, accu) {
           }
         });
   }
-  if (!l2) {
-    return accu;
+  if (l2) {
+    throw new Error("Invalid_argument", {
+          cause: {
+            RE_EXN_ID: "Invalid_argument",
+            _1: "List.fold_right2"
+          }
+        });
   }
-  throw new Error("Invalid_argument", {
-        cause: {
-          RE_EXN_ID: "Invalid_argument",
-          _1: "List.fold_right2"
-        }
-      });
+  return accu;
 }
 
 function for_all(p, _param) {
diff --git a/lib/es6/listLabels.js b/lib/es6/listLabels.js
index 85bb33989a..a12d7fcd6d 100644
--- a/lib/es6/listLabels.js
+++ b/lib/es6/listLabels.js
@@ -155,19 +155,19 @@ function init_aux(i, n, f) {
 }
 
 function init(len, f) {
-  if (len >= 0) {
-    if (len > 10000) {
-      return rev_append(init_tailrec_aux(/* [] */0, 0, len, f), /* [] */0);
-    } else {
-      return init_aux(0, len, f);
-    }
+  if (len < 0) {
+    throw new Error("Invalid_argument", {
+          cause: {
+            RE_EXN_ID: "Invalid_argument",
+            _1: "List.init"
+          }
+        });
+  }
+  if (len > 10000) {
+    return rev_append(init_tailrec_aux(/* [] */0, 0, len, f), /* [] */0);
+  } else {
+    return init_aux(0, len, f);
   }
-  throw new Error("Invalid_argument", {
-        cause: {
-          RE_EXN_ID: "Invalid_argument",
-          _1: "List.init"
-        }
-      });
 }
 
 function flatten(param) {
@@ -323,15 +323,15 @@ function rev_map2(f, l1, l2) {
             }
           });
     }
-    if (!l2$1) {
-      return accu;
+    if (l2$1) {
+      throw new Error("Invalid_argument", {
+            cause: {
+              RE_EXN_ID: "Invalid_argument",
+              _1: "List.rev_map2"
+            }
+          });
     }
-    throw new Error("Invalid_argument", {
-          cause: {
-            RE_EXN_ID: "Invalid_argument",
-            _1: "List.rev_map2"
-          }
-        });
+    return accu;
   };
 }
 
@@ -384,15 +384,15 @@ function fold_left2(f, _accu, _l1, _l2) {
             }
           });
     }
-    if (!l2) {
-      return accu;
+    if (l2) {
+      throw new Error("Invalid_argument", {
+            cause: {
+              RE_EXN_ID: "Invalid_argument",
+              _1: "List.fold_left2"
+            }
+          });
     }
-    throw new Error("Invalid_argument", {
-          cause: {
-            RE_EXN_ID: "Invalid_argument",
-            _1: "List.fold_left2"
-          }
-        });
+    return accu;
   };
 }
 
@@ -408,15 +408,15 @@ function fold_right2(f, l1, l2, accu) {
           }
         });
   }
-  if (!l2) {
-    return accu;
+  if (l2) {
+    throw new Error("Invalid_argument", {
+          cause: {
+            RE_EXN_ID: "Invalid_argument",
+            _1: "List.fold_right2"
+          }
+        });
   }
-  throw new Error("Invalid_argument", {
-        cause: {
-          RE_EXN_ID: "Invalid_argument",
-          _1: "List.fold_right2"
-        }
-      });
+  return accu;
 }
 
 function for_all(p, _param) {
diff --git a/lib/es6/moreLabels.js b/lib/es6/moreLabels.js
index bb08f475a0..d90e8d2957 100644
--- a/lib/es6/moreLabels.js
+++ b/lib/es6/moreLabels.js
@@ -1977,4 +1977,4 @@ export {
   $$Map,
   $$Set,
 }
-/* HashtblLabels Not a pure module */
+/* No side effect */
diff --git a/lib/es6/pervasives.js b/lib/es6/pervasives.js
index e211c20bee..255eeeffc4 100644
--- a/lib/es6/pervasives.js
+++ b/lib/es6/pervasives.js
@@ -185,7 +185,7 @@ function print_int(i) {
 }
 
 function print_float(i) {
-  console.log(string_of_float(i));
+  console.log(valid_float_lexem(Caml_format.format_float("%.12g", i)));
 }
 
 function print_string(prim) {
diff --git a/lib/es6/random.js b/lib/es6/random.js
index c0e7284cf1..e2e703067e 100644
--- a/lib/es6/random.js
+++ b/lib/es6/random.js
@@ -74,65 +74,65 @@ function bits(s) {
 }
 
 function int(s, bound) {
-  if (!(bound > 1073741823 || bound <= 0)) {
-    while(true) {
-      let r = bits(s);
-      let v = r % bound;
-      if ((r - v | 0) <= ((1073741823 - bound | 0) + 1 | 0)) {
-        return v;
-      }
-      continue;
-    };
+  if (bound > 1073741823 || bound <= 0) {
+    throw new Error("Invalid_argument", {
+          cause: {
+            RE_EXN_ID: "Invalid_argument",
+            _1: "Random.int"
+          }
+        });
   }
-  throw new Error("Invalid_argument", {
-        cause: {
-          RE_EXN_ID: "Invalid_argument",
-          _1: "Random.int"
-        }
-      });
+  while(true) {
+    let r = bits(s);
+    let v = r % bound;
+    if ((r - v | 0) <= ((1073741823 - bound | 0) + 1 | 0)) {
+      return v;
+    }
+    continue;
+  };
 }
 
 function int32(s, bound) {
-  if (bound > 0) {
-    while(true) {
-      let b1 = bits(s);
-      let b2 = ((bits(s) & 1) << 30);
-      let r = b1 | b2;
-      let v = r % bound;
-      if ((r - v | 0) <= ((Int32.max_int - bound | 0) + 1 | 0)) {
-        return v;
-      }
-      continue;
-    };
+  if (bound <= 0) {
+    throw new Error("Invalid_argument", {
+          cause: {
+            RE_EXN_ID: "Invalid_argument",
+            _1: "Random.int32"
+          }
+        });
   }
-  throw new Error("Invalid_argument", {
-        cause: {
-          RE_EXN_ID: "Invalid_argument",
-          _1: "Random.int32"
-        }
-      });
+  while(true) {
+    let b1 = bits(s);
+    let b2 = ((bits(s) & 1) << 30);
+    let r = b1 | b2;
+    let v = r % bound;
+    if ((r - v | 0) <= ((Int32.max_int - bound | 0) + 1 | 0)) {
+      return v;
+    }
+    continue;
+  };
 }
 
 function int64(s, bound) {
-  if (!Caml.i64_le(bound, Caml_int64.zero)) {
-    while(true) {
-      let b1 = Caml_int64.of_int32(bits(s));
-      let b2 = Caml_int64.lsl_(Caml_int64.of_int32(bits(s)), 30);
-      let b3 = Caml_int64.lsl_(Caml_int64.of_int32(bits(s) & 7), 60);
-      let r = Caml_int64.or_(b1, Caml_int64.or_(b2, b3));
-      let v = Caml_int64.mod_(r, bound);
-      if (!Caml.i64_gt(Caml_int64.sub(r, v), Caml_int64.add(Caml_int64.sub(Int64.max_int, bound), Caml_int64.one))) {
-        return v;
-      }
-      continue;
-    };
+  if (Caml.i64_le(bound, Caml_int64.zero)) {
+    throw new Error("Invalid_argument", {
+          cause: {
+            RE_EXN_ID: "Invalid_argument",
+            _1: "Random.int64"
+          }
+        });
   }
-  throw new Error("Invalid_argument", {
-        cause: {
-          RE_EXN_ID: "Invalid_argument",
-          _1: "Random.int64"
-        }
-      });
+  while(true) {
+    let b1 = Caml_int64.of_int32(bits(s));
+    let b2 = Caml_int64.lsl_(Caml_int64.of_int32(bits(s)), 30);
+    let b3 = Caml_int64.lsl_(Caml_int64.of_int32(bits(s) & 7), 60);
+    let r = Caml_int64.or_(b1, Caml_int64.or_(b2, b3));
+    let v = Caml_int64.mod_(r, bound);
+    if (!Caml.i64_gt(Caml_int64.sub(r, v), Caml_int64.add(Caml_int64.sub(Int64.max_int, bound), Caml_int64.one))) {
+      return v;
+    }
+    continue;
+  };
 }
 
 function rawfloat(s) {
@@ -227,7 +227,7 @@ function int64$1(bound) {
 }
 
 function float$1(scale) {
-  return float($$default, scale);
+  return rawfloat($$default) * scale;
 }
 
 function bool$1() {
diff --git a/lib/es6/stream.js b/lib/es6/stream.js
index c1fffd51dc..5d6058b378 100644
--- a/lib/es6/stream.js
+++ b/lib/es6/stream.js
@@ -1,6 +1,5 @@
 
 
-import * as Lazy from "./lazy.js";
 import * as List from "./list.js";
 import * as Caml_bytes from "./caml_bytes.js";
 import * as Caml_option from "./caml_option.js";
@@ -362,32 +361,38 @@ function ising(i) {
 }
 
 function lapp(f, s) {
+  let f$1 = function () {
+    return {
+      TAG: "Sapp",
+      _0: data(f()),
+      _1: data(s)
+    };
+  };
   return {
     count: 0,
     data: {
       TAG: "Slazy",
-      _0: Lazy.from_fun(function () {
-        return {
-          TAG: "Sapp",
-          _0: data(f()),
-          _1: data(s)
-        };
+      _0: CamlinternalLazy.from_fun(function () {
+        return f$1();
       })
     }
   };
 }
 
 function lcons(f, s) {
+  let f$1 = function () {
+    return {
+      TAG: "Scons",
+      _0: f(),
+      _1: data(s)
+    };
+  };
   return {
     count: 0,
     data: {
       TAG: "Slazy",
-      _0: Lazy.from_fun(function () {
-        return {
-          TAG: "Scons",
-          _0: f(),
-          _1: data(s)
-        };
+      _0: CamlinternalLazy.from_fun(function () {
+        return f$1();
       })
     }
   };
@@ -398,7 +403,7 @@ function lsing(f) {
     count: 0,
     data: {
       TAG: "Slazy",
-      _0: Lazy.from_fun(function () {
+      _0: CamlinternalLazy.from_fun(function () {
         return {
           TAG: "Scons",
           _0: f(),
@@ -414,7 +419,7 @@ function slazy(f) {
     count: 0,
     data: {
       TAG: "Slazy",
-      _0: Lazy.from_fun(function () {
+      _0: CamlinternalLazy.from_fun(function () {
         return data(f());
       })
     }
diff --git a/lib/es6/string.js b/lib/es6/string.js
index 8fd3ca5035..80b4bd8637 100644
--- a/lib/es6/string.js
+++ b/lib/es6/string.js
@@ -128,28 +128,28 @@ function index_opt(s, c) {
 
 function index_from(s, i, c) {
   let l = s.length;
-  if (!(i < 0 || i > l)) {
-    return index_rec(s, l, i, c);
+  if (i < 0 || i > l) {
+    throw new Error("Invalid_argument", {
+          cause: {
+            RE_EXN_ID: "Invalid_argument",
+            _1: "String.index_from / Bytes.index_from"
+          }
+        });
   }
-  throw new Error("Invalid_argument", {
-        cause: {
-          RE_EXN_ID: "Invalid_argument",
-          _1: "String.index_from / Bytes.index_from"
-        }
-      });
+  return index_rec(s, l, i, c);
 }
 
 function index_from_opt(s, i, c) {
   let l = s.length;
-  if (!(i < 0 || i > l)) {
-    return index_rec_opt(s, l, i, c);
+  if (i < 0 || i > l) {
+    throw new Error("Invalid_argument", {
+          cause: {
+            RE_EXN_ID: "Invalid_argument",
+            _1: "String.index_from_opt / Bytes.index_from_opt"
+          }
+        });
   }
-  throw new Error("Invalid_argument", {
-        cause: {
-          RE_EXN_ID: "Invalid_argument",
-          _1: "String.index_from_opt / Bytes.index_from_opt"
-        }
-      });
+  return index_rec_opt(s, l, i, c);
 }
 
 function rindex_rec(s, _i, c) {
@@ -175,15 +175,15 @@ function rindex(s, c) {
 }
 
 function rindex_from(s, i, c) {
-  if (!(i < -1 || i >= s.length)) {
-    return rindex_rec(s, i, c);
+  if (i < -1 || i >= s.length) {
+    throw new Error("Invalid_argument", {
+          cause: {
+            RE_EXN_ID: "Invalid_argument",
+            _1: "String.rindex_from / Bytes.rindex_from"
+          }
+        });
   }
-  throw new Error("Invalid_argument", {
-        cause: {
-          RE_EXN_ID: "Invalid_argument",
-          _1: "String.rindex_from / Bytes.rindex_from"
-        }
-      });
+  return rindex_rec(s, i, c);
 }
 
 function rindex_rec_opt(s, _i, c) {
@@ -205,15 +205,15 @@ function rindex_opt(s, c) {
 }
 
 function rindex_from_opt(s, i, c) {
-  if (!(i < -1 || i >= s.length)) {
-    return rindex_rec_opt(s, i, c);
+  if (i < -1 || i >= s.length) {
+    throw new Error("Invalid_argument", {
+          cause: {
+            RE_EXN_ID: "Invalid_argument",
+            _1: "String.rindex_from_opt / Bytes.rindex_from_opt"
+          }
+        });
   }
-  throw new Error("Invalid_argument", {
-        cause: {
-          RE_EXN_ID: "Invalid_argument",
-          _1: "String.rindex_from_opt / Bytes.rindex_from_opt"
-        }
-      });
+  return rindex_rec_opt(s, i, c);
 }
 
 function contains_from(s, i, c) {
diff --git a/lib/es6/stringLabels.js b/lib/es6/stringLabels.js
index 3db2216ab3..38232f9ba9 100644
--- a/lib/es6/stringLabels.js
+++ b/lib/es6/stringLabels.js
@@ -14,9 +14,7 @@ function sub(s, ofs, len) {
   return Bytes.unsafe_to_string(Bytes.sub(Bytes.unsafe_of_string(s), ofs, len));
 }
 
-function blit(src, src_pos, dst, dst_pos, len) {
-  Bytes.blit_string(src, src_pos, dst, dst_pos, len);
-}
+let blit = Bytes.blit_string;
 
 function concat(sep, xs) {
   return $$Array.of_list(xs).join(sep);
@@ -132,28 +130,28 @@ function index_opt(s, c) {
 
 function index_from(s, i, c) {
   let l = s.length;
-  if (!(i < 0 || i > l)) {
-    return index_rec(s, l, i, c);
+  if (i < 0 || i > l) {
+    throw new Error("Invalid_argument", {
+          cause: {
+            RE_EXN_ID: "Invalid_argument",
+            _1: "String.index_from / Bytes.index_from"
+          }
+        });
   }
-  throw new Error("Invalid_argument", {
-        cause: {
-          RE_EXN_ID: "Invalid_argument",
-          _1: "String.index_from / Bytes.index_from"
-        }
-      });
+  return index_rec(s, l, i, c);
 }
 
 function index_from_opt(s, i, c) {
   let l = s.length;
-  if (!(i < 0 || i > l)) {
-    return index_rec_opt(s, l, i, c);
+  if (i < 0 || i > l) {
+    throw new Error("Invalid_argument", {
+          cause: {
+            RE_EXN_ID: "Invalid_argument",
+            _1: "String.index_from_opt / Bytes.index_from_opt"
+          }
+        });
   }
-  throw new Error("Invalid_argument", {
-        cause: {
-          RE_EXN_ID: "Invalid_argument",
-          _1: "String.index_from_opt / Bytes.index_from_opt"
-        }
-      });
+  return index_rec_opt(s, l, i, c);
 }
 
 function rindex_rec(s, _i, c) {
@@ -179,15 +177,15 @@ function rindex(s, c) {
 }
 
 function rindex_from(s, i, c) {
-  if (!(i < -1 || i >= s.length)) {
-    return rindex_rec(s, i, c);
+  if (i < -1 || i >= s.length) {
+    throw new Error("Invalid_argument", {
+          cause: {
+            RE_EXN_ID: "Invalid_argument",
+            _1: "String.rindex_from / Bytes.rindex_from"
+          }
+        });
   }
-  throw new Error("Invalid_argument", {
-        cause: {
-          RE_EXN_ID: "Invalid_argument",
-          _1: "String.rindex_from / Bytes.rindex_from"
-        }
-      });
+  return rindex_rec(s, i, c);
 }
 
 function rindex_rec_opt(s, _i, c) {
@@ -209,15 +207,15 @@ function rindex_opt(s, c) {
 }
 
 function rindex_from_opt(s, i, c) {
-  if (!(i < -1 || i >= s.length)) {
-    return rindex_rec_opt(s, i, c);
+  if (i < -1 || i >= s.length) {
+    throw new Error("Invalid_argument", {
+          cause: {
+            RE_EXN_ID: "Invalid_argument",
+            _1: "String.rindex_from_opt / Bytes.rindex_from_opt"
+          }
+        });
   }
-  throw new Error("Invalid_argument", {
-        cause: {
-          RE_EXN_ID: "Invalid_argument",
-          _1: "String.rindex_from_opt / Bytes.rindex_from_opt"
-        }
-      });
+  return rindex_rec_opt(s, i, c);
 }
 
 function contains_from(s, i, c) {
diff --git a/lib/es6/sys.js b/lib/es6/sys.js
index 7ddb3c3ddd..1ded50c6ab 100644
--- a/lib/es6/sys.js
+++ b/lib/es6/sys.js
@@ -45,20 +45,7 @@ function set_signal(sig_num, sig_beh) {
 let Break = /* @__PURE__ */Caml_exceptions.create("Sys.Break");
 
 function catch_break(on) {
-  if (on) {
-    return set_signal(-6, {
-      TAG: "Signal_handle",
-      _0: (function (param) {
-        throw new Error(Break, {
-              cause: {
-                RE_EXN_ID: Break
-              }
-            });
-      })
-    });
-  } else {
-    return set_signal(-6, "Signal_default");
-  }
+  
 }
 
 function enable_runtime_warnings(param) {
diff --git a/lib/es6/uchar.js b/lib/es6/uchar.js
index cfb8c42324..f98c218a31 100644
--- a/lib/es6/uchar.js
+++ b/lib/es6/uchar.js
@@ -15,30 +15,30 @@ function succ(u) {
   if (u === 55295) {
     return 57344;
   }
-  if (u !== 1114111) {
-    return u + 1 | 0;
+  if (u === 1114111) {
+    throw new Error("Invalid_argument", {
+          cause: {
+            RE_EXN_ID: "Invalid_argument",
+            _1: "U+10FFFF has no successor"
+          }
+        });
   }
-  throw new Error("Invalid_argument", {
-        cause: {
-          RE_EXN_ID: "Invalid_argument",
-          _1: "U+10FFFF has no successor"
-        }
-      });
+  return u + 1 | 0;
 }
 
 function pred(u) {
   if (u === 57344) {
     return 55295;
   }
-  if (u !== 0) {
-    return u - 1 | 0;
+  if (u === 0) {
+    throw new Error("Invalid_argument", {
+          cause: {
+            RE_EXN_ID: "Invalid_argument",
+            _1: "U+0000 has no predecessor"
+          }
+        });
   }
-  throw new Error("Invalid_argument", {
-        cause: {
-          RE_EXN_ID: "Invalid_argument",
-          _1: "U+0000 has no predecessor"
-        }
-      });
+  return u - 1 | 0;
 }
 
 function is_valid(i) {
diff --git a/lib/js/array.js b/lib/js/array.js
index 5580be4143..9407d2ffc0 100644
--- a/lib/js/array.js
+++ b/lib/js/array.js
@@ -57,15 +57,15 @@ function append(a1, a2) {
 }
 
 function sub(a, ofs, len) {
-  if (!(ofs < 0 || len < 0 || ofs > (a.length - len | 0))) {
-    return Caml_array.sub(a, ofs, len);
+  if (ofs < 0 || len < 0 || ofs > (a.length - len | 0)) {
+    throw new Error("Invalid_argument", {
+          cause: {
+            RE_EXN_ID: "Invalid_argument",
+            _1: "Array.sub"
+          }
+        });
   }
-  throw new Error("Invalid_argument", {
-        cause: {
-          RE_EXN_ID: "Invalid_argument",
-          _1: "Array.sub"
-        }
-      });
+  return Caml_array.sub(a, ofs, len);
 }
 
 function fill(a, ofs, len, v) {
@@ -83,15 +83,15 @@ function fill(a, ofs, len, v) {
 }
 
 function blit(a1, ofs1, a2, ofs2, len) {
-  if (!(len < 0 || ofs1 < 0 || ofs1 > (a1.length - len | 0) || ofs2 < 0 || ofs2 > (a2.length - len | 0))) {
-    return Caml_array.blit(a1, ofs1, a2, ofs2, len);
+  if (len < 0 || ofs1 < 0 || ofs1 > (a1.length - len | 0) || ofs2 < 0 || ofs2 > (a2.length - len | 0)) {
+    throw new Error("Invalid_argument", {
+          cause: {
+            RE_EXN_ID: "Invalid_argument",
+            _1: "Array.blit"
+          }
+        });
   }
-  throw new Error("Invalid_argument", {
-        cause: {
-          RE_EXN_ID: "Invalid_argument",
-          _1: "Array.blit"
-        }
-      });
+  Caml_array.blit(a1, ofs1, a2, ofs2, len);
 }
 
 function iter(f, a) {
diff --git a/lib/js/arrayLabels.js b/lib/js/arrayLabels.js
index 961b8f8729..c486cfe363 100644
--- a/lib/js/arrayLabels.js
+++ b/lib/js/arrayLabels.js
@@ -57,15 +57,15 @@ function append(a1, a2) {
 }
 
 function sub(a, ofs, len) {
-  if (!(ofs < 0 || len < 0 || ofs > (a.length - len | 0))) {
-    return Caml_array.sub(a, ofs, len);
+  if (ofs < 0 || len < 0 || ofs > (a.length - len | 0)) {
+    throw new Error("Invalid_argument", {
+          cause: {
+            RE_EXN_ID: "Invalid_argument",
+            _1: "Array.sub"
+          }
+        });
   }
-  throw new Error("Invalid_argument", {
-        cause: {
-          RE_EXN_ID: "Invalid_argument",
-          _1: "Array.sub"
-        }
-      });
+  return Caml_array.sub(a, ofs, len);
 }
 
 function fill(a, ofs, len, v) {
@@ -83,15 +83,15 @@ function fill(a, ofs, len, v) {
 }
 
 function blit(a1, ofs1, a2, ofs2, len) {
-  if (!(len < 0 || ofs1 < 0 || ofs1 > (a1.length - len | 0) || ofs2 < 0 || ofs2 > (a2.length - len | 0))) {
-    return Caml_array.blit(a1, ofs1, a2, ofs2, len);
+  if (len < 0 || ofs1 < 0 || ofs1 > (a1.length - len | 0) || ofs2 < 0 || ofs2 > (a2.length - len | 0)) {
+    throw new Error("Invalid_argument", {
+          cause: {
+            RE_EXN_ID: "Invalid_argument",
+            _1: "Array.blit"
+          }
+        });
   }
-  throw new Error("Invalid_argument", {
-        cause: {
-          RE_EXN_ID: "Invalid_argument",
-          _1: "Array.blit"
-        }
-      });
+  Caml_array.blit(a1, ofs1, a2, ofs2, len);
 }
 
 function iter(f, a) {
diff --git a/lib/js/belt_Array.js b/lib/js/belt_Array.js
index 905ed7fa04..596da5e5c6 100644
--- a/lib/js/belt_Array.js
+++ b/lib/js/belt_Array.js
@@ -325,9 +325,9 @@ function flatMapU(a, f) {
 }
 
 function flatMap(a, f) {
-  return flatMapU(a, (function (a) {
+  return concatMany(mapU(a, (function (a) {
     return f(a);
-  }));
+  })));
 }
 
 function getByU(a, p) {
diff --git a/lib/js/belt_HashMapInt.js b/lib/js/belt_HashMapInt.js
index 69e651f5a1..7c91e287d5 100644
--- a/lib/js/belt_HashMapInt.js
+++ b/lib/js/belt_HashMapInt.js
@@ -193,7 +193,7 @@ function size(h) {
 
 function fromArray(arr) {
   let len = arr.length;
-  let v = make(len);
+  let v = Belt_internalBucketsType.make(undefined, undefined, len);
   for(let i = 0; i < len; ++i){
     let match = arr[i];
     set(v, match[0], match[1]);
diff --git a/lib/js/belt_HashMapString.js b/lib/js/belt_HashMapString.js
index ee4a0d8f31..258b989a29 100644
--- a/lib/js/belt_HashMapString.js
+++ b/lib/js/belt_HashMapString.js
@@ -193,7 +193,7 @@ function size(h) {
 
 function fromArray(arr) {
   let len = arr.length;
-  let v = make(len);
+  let v = Belt_internalBucketsType.make(undefined, undefined, len);
   for(let i = 0; i < len; ++i){
     let match = arr[i];
     set(v, match[0], match[1]);
diff --git a/lib/js/belt_Map.js b/lib/js/belt_Map.js
index 3db312ce0c..dfbf259132 100644
--- a/lib/js/belt_Map.js
+++ b/lib/js/belt_Map.js
@@ -112,7 +112,7 @@ function findFirstByU(m, f) {
 }
 
 function findFirstBy(m, f) {
-  return findFirstByU(m, (function (a, b) {
+  return Belt_MapDict.findFirstByU(m.data, (function (a, b) {
     return f(a, b);
   }));
 }
@@ -122,7 +122,7 @@ function forEachU(m, f) {
 }
 
 function forEach(m, f) {
-  forEachU(m, (function (a, b) {
+  Belt_MapDict.forEachU(m.data, (function (a, b) {
     f(a, b);
   }));
 }
@@ -142,7 +142,7 @@ function everyU(m, f) {
 }
 
 function every(m, f) {
-  return everyU(m, (function (a, b) {
+  return Belt_MapDict.everyU(m.data, (function (a, b) {
     return f(a, b);
   }));
 }
@@ -152,7 +152,7 @@ function someU(m, f) {
 }
 
 function some(m, f) {
-  return someU(m, (function (a, b) {
+  return Belt_MapDict.someU(m.data, (function (a, b) {
     return f(a, b);
   }));
 }
diff --git a/lib/js/belt_MutableMap.js b/lib/js/belt_MutableMap.js
index 13e20ff3c9..9da165b978 100644
--- a/lib/js/belt_MutableMap.js
+++ b/lib/js/belt_MutableMap.js
@@ -153,7 +153,8 @@ function clear(m) {
 }
 
 function isEmpty(d) {
-  return d.data === undefined;
+  let x = d.data;
+  return x === undefined;
 }
 
 function minKey(m) {
@@ -193,7 +194,7 @@ function forEachU(d, f) {
 }
 
 function forEach(d, f) {
-  forEachU(d, (function (a, b) {
+  Belt_internalAVLtree.forEachU(d.data, (function (a, b) {
     f(a, b);
   }));
 }
@@ -213,7 +214,7 @@ function everyU(d, p) {
 }
 
 function every(d, p) {
-  return everyU(d, (function (a, b) {
+  return Belt_internalAVLtree.everyU(d.data, (function (a, b) {
     return p(a, b);
   }));
 }
@@ -223,7 +224,7 @@ function someU(d, p) {
 }
 
 function some(d, p) {
-  return someU(d, (function (a, b) {
+  return Belt_internalAVLtree.someU(d.data, (function (a, b) {
     return p(a, b);
   }));
 }
diff --git a/lib/js/belt_MutableMapInt.js b/lib/js/belt_MutableMapInt.js
index abc68b02b1..fed12a58e2 100644
--- a/lib/js/belt_MutableMapInt.js
+++ b/lib/js/belt_MutableMapInt.js
@@ -11,7 +11,8 @@ function make() {
 }
 
 function isEmpty(m) {
-  return m.data === undefined;
+  let x = m.data;
+  return x === undefined;
 }
 
 function clear(m) {
@@ -65,7 +66,7 @@ function forEachU(d, f) {
 }
 
 function forEach(d, f) {
-  forEachU(d, (function (a, b) {
+  Belt_internalAVLtree.forEachU(d.data, (function (a, b) {
     f(a, b);
   }));
 }
@@ -109,7 +110,7 @@ function everyU(d, f) {
 }
 
 function every(d, f) {
-  return everyU(d, (function (a, b) {
+  return Belt_internalAVLtree.everyU(d.data, (function (a, b) {
     return f(a, b);
   }));
 }
@@ -119,7 +120,7 @@ function someU(d, f) {
 }
 
 function some(d, f) {
-  return someU(d, (function (a, b) {
+  return Belt_internalAVLtree.someU(d.data, (function (a, b) {
     return f(a, b);
   }));
 }
diff --git a/lib/js/belt_MutableMapString.js b/lib/js/belt_MutableMapString.js
index 0db5237044..50346ce2ce 100644
--- a/lib/js/belt_MutableMapString.js
+++ b/lib/js/belt_MutableMapString.js
@@ -11,7 +11,8 @@ function make() {
 }
 
 function isEmpty(m) {
-  return m.data === undefined;
+  let x = m.data;
+  return x === undefined;
 }
 
 function clear(m) {
@@ -65,7 +66,7 @@ function forEachU(d, f) {
 }
 
 function forEach(d, f) {
-  forEachU(d, (function (a, b) {
+  Belt_internalAVLtree.forEachU(d.data, (function (a, b) {
     f(a, b);
   }));
 }
@@ -109,7 +110,7 @@ function everyU(d, f) {
 }
 
 function every(d, f) {
-  return everyU(d, (function (a, b) {
+  return Belt_internalAVLtree.everyU(d.data, (function (a, b) {
     return f(a, b);
   }));
 }
@@ -119,7 +120,7 @@ function someU(d, f) {
 }
 
 function some(d, f) {
-  return someU(d, (function (a, b) {
+  return Belt_internalAVLtree.someU(d.data, (function (a, b) {
     return f(a, b);
   }));
 }
diff --git a/lib/js/belt_MutableSet.js b/lib/js/belt_MutableSet.js
index 6b94e54528..bc44cafdd5 100644
--- a/lib/js/belt_MutableSet.js
+++ b/lib/js/belt_MutableSet.js
@@ -192,7 +192,8 @@ function make(id) {
 }
 
 function isEmpty(d) {
-  return d.data === undefined;
+  let n = d.data;
+  return n === undefined;
 }
 
 function minimum(d) {
@@ -216,7 +217,7 @@ function forEachU(d, f) {
 }
 
 function forEach(d, f) {
-  forEachU(d, (function (a) {
+  Belt_internalAVLset.forEachU(d.data, (function (a) {
     f(a);
   }));
 }
@@ -236,7 +237,7 @@ function everyU(d, p) {
 }
 
 function every(d, p) {
-  return everyU(d, (function (a) {
+  return Belt_internalAVLset.everyU(d.data, (function (a) {
     return p(a);
   }));
 }
@@ -246,7 +247,7 @@ function someU(d, p) {
 }
 
 function some(d, p) {
-  return someU(d, (function (a) {
+  return Belt_internalAVLset.someU(d.data, (function (a) {
     return p(a);
   }));
 }
diff --git a/lib/js/belt_MutableSetInt.js b/lib/js/belt_MutableSetInt.js
index 691e015f3e..830f3b4e26 100644
--- a/lib/js/belt_MutableSetInt.js
+++ b/lib/js/belt_MutableSetInt.js
@@ -189,7 +189,8 @@ function make() {
 }
 
 function isEmpty(d) {
-  return d.data === undefined;
+  let n = d.data;
+  return n === undefined;
 }
 
 function minimum(d) {
@@ -213,7 +214,7 @@ function forEachU(d, f) {
 }
 
 function forEach(d, f) {
-  forEachU(d, (function (a) {
+  Belt_internalAVLset.forEachU(d.data, (function (a) {
     f(a);
   }));
 }
@@ -233,7 +234,7 @@ function everyU(d, p) {
 }
 
 function every(d, p) {
-  return everyU(d, (function (a) {
+  return Belt_internalAVLset.everyU(d.data, (function (a) {
     return p(a);
   }));
 }
@@ -243,7 +244,7 @@ function someU(d, p) {
 }
 
 function some(d, p) {
-  return someU(d, (function (a) {
+  return Belt_internalAVLset.someU(d.data, (function (a) {
     return p(a);
   }));
 }
diff --git a/lib/js/belt_MutableSetString.js b/lib/js/belt_MutableSetString.js
index c13ba1c2dc..f7a1bbd568 100644
--- a/lib/js/belt_MutableSetString.js
+++ b/lib/js/belt_MutableSetString.js
@@ -189,7 +189,8 @@ function make() {
 }
 
 function isEmpty(d) {
-  return d.data === undefined;
+  let n = d.data;
+  return n === undefined;
 }
 
 function minimum(d) {
@@ -213,7 +214,7 @@ function forEachU(d, f) {
 }
 
 function forEach(d, f) {
-  forEachU(d, (function (a) {
+  Belt_internalAVLset.forEachU(d.data, (function (a) {
     f(a);
   }));
 }
@@ -233,7 +234,7 @@ function everyU(d, p) {
 }
 
 function every(d, p) {
-  return everyU(d, (function (a) {
+  return Belt_internalAVLset.everyU(d.data, (function (a) {
     return p(a);
   }));
 }
@@ -243,7 +244,7 @@ function someU(d, p) {
 }
 
 function some(d, p) {
-  return someU(d, (function (a) {
+  return Belt_internalAVLset.someU(d.data, (function (a) {
     return p(a);
   }));
 }
diff --git a/lib/js/belt_Set.js b/lib/js/belt_Set.js
index f159790896..621ccdf2ef 100644
--- a/lib/js/belt_Set.js
+++ b/lib/js/belt_Set.js
@@ -127,7 +127,7 @@ function forEachU(m, f) {
 }
 
 function forEach(m, f) {
-  forEachU(m, (function (a) {
+  Belt_SetDict.forEachU(m.data, (function (a) {
     f(a);
   }));
 }
@@ -147,7 +147,7 @@ function everyU(m, f) {
 }
 
 function every(m, f) {
-  return everyU(m, (function (a) {
+  return Belt_SetDict.everyU(m.data, (function (a) {
     return f(a);
   }));
 }
@@ -157,7 +157,7 @@ function someU(m, f) {
 }
 
 function some(m, f) {
-  return someU(m, (function (a) {
+  return Belt_SetDict.someU(m.data, (function (a) {
     return f(a);
   }));
 }
diff --git a/lib/js/belt_internalBuckets.js b/lib/js/belt_internalBuckets.js
index 21423c0177..bde6492a04 100644
--- a/lib/js/belt_internalBuckets.js
+++ b/lib/js/belt_internalBuckets.js
@@ -3,19 +3,6 @@
 let Belt_Array = require("./belt_Array.js");
 let Caml_option = require("./caml_option.js");
 
-function copyBucket(c) {
-  if (c === undefined) {
-    return c;
-  }
-  let head = {
-    key: c.key,
-    value: c.value,
-    next: undefined
-  };
-  copyAuxCont(c.next, head);
-  return head;
-}
-
 function copyAuxCont(_c, _prec) {
   while(true) {
     let prec = _prec;
@@ -35,6 +22,19 @@ function copyAuxCont(_c, _prec) {
   };
 }
 
+function copyBucket(c) {
+  if (c === undefined) {
+    return c;
+  }
+  let head = {
+    key: c.key,
+    value: c.value,
+    next: undefined
+  };
+  copyAuxCont(c.next, head);
+  return head;
+}
+
 function copyBuckets(buckets) {
   let len = buckets.length;
   let newBuckets = new Array(len);
diff --git a/lib/js/buffer.js b/lib/js/buffer.js
index 160c5a977f..1841872741 100644
--- a/lib/js/buffer.js
+++ b/lib/js/buffer.js
@@ -25,39 +25,39 @@ function to_bytes(b) {
 }
 
 function sub(b, ofs, len) {
-  if (!(ofs < 0 || len < 0 || ofs > (b.position - len | 0))) {
-    return Bytes.sub_string(b.buffer, ofs, len);
+  if (ofs < 0 || len < 0 || ofs > (b.position - len | 0)) {
+    throw new Error("Invalid_argument", {
+          cause: {
+            RE_EXN_ID: "Invalid_argument",
+            _1: "Buffer.sub"
+          }
+        });
   }
-  throw new Error("Invalid_argument", {
-        cause: {
-          RE_EXN_ID: "Invalid_argument",
-          _1: "Buffer.sub"
-        }
-      });
+  return Bytes.sub_string(b.buffer, ofs, len);
 }
 
 function blit(src, srcoff, dst, dstoff, len) {
-  if (!(len < 0 || srcoff < 0 || srcoff > (src.position - len | 0) || dstoff < 0 || dstoff > (dst.length - len | 0))) {
-    return Bytes.blit(src.buffer, srcoff, dst, dstoff, len);
+  if (len < 0 || srcoff < 0 || srcoff > (src.position - len | 0) || dstoff < 0 || dstoff > (dst.length - len | 0)) {
+    throw new Error("Invalid_argument", {
+          cause: {
+            RE_EXN_ID: "Invalid_argument",
+            _1: "Buffer.blit"
+          }
+        });
   }
-  throw new Error("Invalid_argument", {
-        cause: {
-          RE_EXN_ID: "Invalid_argument",
-          _1: "Buffer.blit"
-        }
-      });
+  Bytes.blit(src.buffer, srcoff, dst, dstoff, len);
 }
 
 function nth(b, ofs) {
-  if (!(ofs < 0 || ofs >= b.position)) {
-    return b.buffer[ofs];
+  if (ofs < 0 || ofs >= b.position) {
+    throw new Error("Invalid_argument", {
+          cause: {
+            RE_EXN_ID: "Invalid_argument",
+            _1: "Buffer.nth"
+          }
+        });
   }
-  throw new Error("Invalid_argument", {
-        cause: {
-          RE_EXN_ID: "Invalid_argument",
-          _1: "Buffer.nth"
-        }
-      });
+  return b.buffer[ofs];
 }
 
 function length(b) {
@@ -454,16 +454,15 @@ function add_substitute(b, f, s) {
 }
 
 function truncate(b, len) {
-  if (!(len < 0 || len > b.position)) {
-    b.position = len;
-    return;
+  if (len < 0 || len > b.position) {
+    throw new Error("Invalid_argument", {
+          cause: {
+            RE_EXN_ID: "Invalid_argument",
+            _1: "Buffer.truncate"
+          }
+        });
   }
-  throw new Error("Invalid_argument", {
-        cause: {
-          RE_EXN_ID: "Invalid_argument",
-          _1: "Buffer.truncate"
-        }
-      });
+  b.position = len;
 }
 
 exports.create = create;
diff --git a/lib/js/bytes.js b/lib/js/bytes.js
index c8dd7b3cac..e1a49076b5 100644
--- a/lib/js/bytes.js
+++ b/lib/js/bytes.js
@@ -148,15 +148,15 @@ function $plus$plus(a, b) {
   if (match$1) {
     return c;
   }
-  if (!match$2) {
-    return c;
+  if (match$2) {
+    throw new Error("Invalid_argument", {
+          cause: {
+            RE_EXN_ID: "Invalid_argument",
+            _1: "Bytes.extend"
+          }
+        });
   }
-  throw new Error("Invalid_argument", {
-        cause: {
-          RE_EXN_ID: "Invalid_argument",
-          _1: "Bytes.extend"
-        }
-      });
+  return c;
 }
 
 function extend(s, left, right) {
@@ -179,55 +179,54 @@ function extend(s, left, right) {
 }
 
 function fill(s, ofs, len, c) {
-  if (!(ofs < 0 || len < 0 || ofs > (s.length - len | 0))) {
-    return unsafe_fill(s, ofs, len, c);
+  if (ofs < 0 || len < 0 || ofs > (s.length - len | 0)) {
+    throw new Error("Invalid_argument", {
+          cause: {
+            RE_EXN_ID: "Invalid_argument",
+            _1: "String.fill / Bytes.fill"
+          }
+        });
   }
-  throw new Error("Invalid_argument", {
-        cause: {
-          RE_EXN_ID: "Invalid_argument",
-          _1: "String.fill / Bytes.fill"
-        }
-      });
+  unsafe_fill(s, ofs, len, c);
 }
 
 function blit(s1, ofs1, s2, ofs2, len) {
-  if (!(len < 0 || ofs1 < 0 || ofs1 > (s1.length - len | 0) || ofs2 < 0 || ofs2 > (s2.length - len | 0))) {
-    return unsafe_blit(s1, ofs1, s2, ofs2, len);
+  if (len < 0 || ofs1 < 0 || ofs1 > (s1.length - len | 0) || ofs2 < 0 || ofs2 > (s2.length - len | 0)) {
+    throw new Error("Invalid_argument", {
+          cause: {
+            RE_EXN_ID: "Invalid_argument",
+            _1: "Bytes.blit"
+          }
+        });
   }
-  throw new Error("Invalid_argument", {
-        cause: {
-          RE_EXN_ID: "Invalid_argument",
-          _1: "Bytes.blit"
-        }
-      });
+  unsafe_blit(s1, ofs1, s2, ofs2, len);
 }
 
 function blit_string(s1, ofs1, s2, ofs2, len) {
-  if (!(len < 0 || ofs1 < 0 || ofs1 > (s1.length - len | 0) || ofs2 < 0 || ofs2 > (s2.length - len | 0))) {
-    if (len <= 0) {
-      return;
-    }
-    let off1 = s1.length - ofs1 | 0;
-    if (len <= off1) {
-      for(let i = 0; i < len; ++i){
-        s2[ofs2 + i | 0] = s1.codePointAt(ofs1 + i | 0);
-      }
-      return;
-    }
-    for(let i$1 = 0; i$1 < off1; ++i$1){
-      s2[ofs2 + i$1 | 0] = s1.codePointAt(ofs1 + i$1 | 0);
-    }
-    for(let i$2 = off1; i$2 < len; ++i$2){
-      s2[ofs2 + i$2 | 0] = /* '\000' */0;
+  if (len < 0 || ofs1 < 0 || ofs1 > (s1.length - len | 0) || ofs2 < 0 || ofs2 > (s2.length - len | 0)) {
+    throw new Error("Invalid_argument", {
+          cause: {
+            RE_EXN_ID: "Invalid_argument",
+            _1: "String.blit / Bytes.blit_string"
+          }
+        });
+  }
+  if (len <= 0) {
+    return;
+  }
+  let off1 = s1.length - ofs1 | 0;
+  if (len <= off1) {
+    for(let i = 0; i < len; ++i){
+      s2[ofs2 + i | 0] = s1.codePointAt(ofs1 + i | 0);
     }
     return;
   }
-  throw new Error("Invalid_argument", {
-        cause: {
-          RE_EXN_ID: "Invalid_argument",
-          _1: "String.blit / Bytes.blit_string"
-        }
-      });
+  for(let i$1 = 0; i$1 < off1; ++i$1){
+    s2[ofs2 + i$1 | 0] = s1.codePointAt(ofs1 + i$1 | 0);
+  }
+  for(let i$2 = off1; i$2 < len; ++i$2){
+    s2[ofs2 + i$2 | 0] = /* '\000' */0;
+  }
 }
 
 function iter(f, a) {
@@ -530,28 +529,28 @@ function index_opt(s, c) {
 
 function index_from(s, i, c) {
   let l = s.length;
-  if (!(i < 0 || i > l)) {
-    return index_rec(s, l, i, c);
+  if (i < 0 || i > l) {
+    throw new Error("Invalid_argument", {
+          cause: {
+            RE_EXN_ID: "Invalid_argument",
+            _1: "String.index_from / Bytes.index_from"
+          }
+        });
   }
-  throw new Error("Invalid_argument", {
-        cause: {
-          RE_EXN_ID: "Invalid_argument",
-          _1: "String.index_from / Bytes.index_from"
-        }
-      });
+  return index_rec(s, l, i, c);
 }
 
 function index_from_opt(s, i, c) {
   let l = s.length;
-  if (!(i < 0 || i > l)) {
-    return index_rec_opt(s, l, i, c);
+  if (i < 0 || i > l) {
+    throw new Error("Invalid_argument", {
+          cause: {
+            RE_EXN_ID: "Invalid_argument",
+            _1: "String.index_from_opt / Bytes.index_from_opt"
+          }
+        });
   }
-  throw new Error("Invalid_argument", {
-        cause: {
-          RE_EXN_ID: "Invalid_argument",
-          _1: "String.index_from_opt / Bytes.index_from_opt"
-        }
-      });
+  return index_rec_opt(s, l, i, c);
 }
 
 function rindex_rec(s, _i, c) {
@@ -577,15 +576,15 @@ function rindex(s, c) {
 }
 
 function rindex_from(s, i, c) {
-  if (!(i < -1 || i >= s.length)) {
-    return rindex_rec(s, i, c);
+  if (i < -1 || i >= s.length) {
+    throw new Error("Invalid_argument", {
+          cause: {
+            RE_EXN_ID: "Invalid_argument",
+            _1: "String.rindex_from / Bytes.rindex_from"
+          }
+        });
   }
-  throw new Error("Invalid_argument", {
-        cause: {
-          RE_EXN_ID: "Invalid_argument",
-          _1: "String.rindex_from / Bytes.rindex_from"
-        }
-      });
+  return rindex_rec(s, i, c);
 }
 
 function rindex_rec_opt(s, _i, c) {
@@ -607,15 +606,15 @@ function rindex_opt(s, c) {
 }
 
 function rindex_from_opt(s, i, c) {
-  if (!(i < -1 || i >= s.length)) {
-    return rindex_rec_opt(s, i, c);
+  if (i < -1 || i >= s.length) {
+    throw new Error("Invalid_argument", {
+          cause: {
+            RE_EXN_ID: "Invalid_argument",
+            _1: "String.rindex_from_opt / Bytes.rindex_from_opt"
+          }
+        });
   }
-  throw new Error("Invalid_argument", {
-        cause: {
-          RE_EXN_ID: "Invalid_argument",
-          _1: "String.rindex_from_opt / Bytes.rindex_from_opt"
-        }
-      });
+  return rindex_rec_opt(s, i, c);
 }
 
 function contains_from(s, i, c) {
diff --git a/lib/js/bytesLabels.js b/lib/js/bytesLabels.js
index c8dd7b3cac..e1a49076b5 100644
--- a/lib/js/bytesLabels.js
+++ b/lib/js/bytesLabels.js
@@ -148,15 +148,15 @@ function $plus$plus(a, b) {
   if (match$1) {
     return c;
   }
-  if (!match$2) {
-    return c;
+  if (match$2) {
+    throw new Error("Invalid_argument", {
+          cause: {
+            RE_EXN_ID: "Invalid_argument",
+            _1: "Bytes.extend"
+          }
+        });
   }
-  throw new Error("Invalid_argument", {
-        cause: {
-          RE_EXN_ID: "Invalid_argument",
-          _1: "Bytes.extend"
-        }
-      });
+  return c;
 }
 
 function extend(s, left, right) {
@@ -179,55 +179,54 @@ function extend(s, left, right) {
 }
 
 function fill(s, ofs, len, c) {
-  if (!(ofs < 0 || len < 0 || ofs > (s.length - len | 0))) {
-    return unsafe_fill(s, ofs, len, c);
+  if (ofs < 0 || len < 0 || ofs > (s.length - len | 0)) {
+    throw new Error("Invalid_argument", {
+          cause: {
+            RE_EXN_ID: "Invalid_argument",
+            _1: "String.fill / Bytes.fill"
+          }
+        });
   }
-  throw new Error("Invalid_argument", {
-        cause: {
-          RE_EXN_ID: "Invalid_argument",
-          _1: "String.fill / Bytes.fill"
-        }
-      });
+  unsafe_fill(s, ofs, len, c);
 }
 
 function blit(s1, ofs1, s2, ofs2, len) {
-  if (!(len < 0 || ofs1 < 0 || ofs1 > (s1.length - len | 0) || ofs2 < 0 || ofs2 > (s2.length - len | 0))) {
-    return unsafe_blit(s1, ofs1, s2, ofs2, len);
+  if (len < 0 || ofs1 < 0 || ofs1 > (s1.length - len | 0) || ofs2 < 0 || ofs2 > (s2.length - len | 0)) {
+    throw new Error("Invalid_argument", {
+          cause: {
+            RE_EXN_ID: "Invalid_argument",
+            _1: "Bytes.blit"
+          }
+        });
   }
-  throw new Error("Invalid_argument", {
-        cause: {
-          RE_EXN_ID: "Invalid_argument",
-          _1: "Bytes.blit"
-        }
-      });
+  unsafe_blit(s1, ofs1, s2, ofs2, len);
 }
 
 function blit_string(s1, ofs1, s2, ofs2, len) {
-  if (!(len < 0 || ofs1 < 0 || ofs1 > (s1.length - len | 0) || ofs2 < 0 || ofs2 > (s2.length - len | 0))) {
-    if (len <= 0) {
-      return;
-    }
-    let off1 = s1.length - ofs1 | 0;
-    if (len <= off1) {
-      for(let i = 0; i < len; ++i){
-        s2[ofs2 + i | 0] = s1.codePointAt(ofs1 + i | 0);
-      }
-      return;
-    }
-    for(let i$1 = 0; i$1 < off1; ++i$1){
-      s2[ofs2 + i$1 | 0] = s1.codePointAt(ofs1 + i$1 | 0);
-    }
-    for(let i$2 = off1; i$2 < len; ++i$2){
-      s2[ofs2 + i$2 | 0] = /* '\000' */0;
+  if (len < 0 || ofs1 < 0 || ofs1 > (s1.length - len | 0) || ofs2 < 0 || ofs2 > (s2.length - len | 0)) {
+    throw new Error("Invalid_argument", {
+          cause: {
+            RE_EXN_ID: "Invalid_argument",
+            _1: "String.blit / Bytes.blit_string"
+          }
+        });
+  }
+  if (len <= 0) {
+    return;
+  }
+  let off1 = s1.length - ofs1 | 0;
+  if (len <= off1) {
+    for(let i = 0; i < len; ++i){
+      s2[ofs2 + i | 0] = s1.codePointAt(ofs1 + i | 0);
     }
     return;
   }
-  throw new Error("Invalid_argument", {
-        cause: {
-          RE_EXN_ID: "Invalid_argument",
-          _1: "String.blit / Bytes.blit_string"
-        }
-      });
+  for(let i$1 = 0; i$1 < off1; ++i$1){
+    s2[ofs2 + i$1 | 0] = s1.codePointAt(ofs1 + i$1 | 0);
+  }
+  for(let i$2 = off1; i$2 < len; ++i$2){
+    s2[ofs2 + i$2 | 0] = /* '\000' */0;
+  }
 }
 
 function iter(f, a) {
@@ -530,28 +529,28 @@ function index_opt(s, c) {
 
 function index_from(s, i, c) {
   let l = s.length;
-  if (!(i < 0 || i > l)) {
-    return index_rec(s, l, i, c);
+  if (i < 0 || i > l) {
+    throw new Error("Invalid_argument", {
+          cause: {
+            RE_EXN_ID: "Invalid_argument",
+            _1: "String.index_from / Bytes.index_from"
+          }
+        });
   }
-  throw new Error("Invalid_argument", {
-        cause: {
-          RE_EXN_ID: "Invalid_argument",
-          _1: "String.index_from / Bytes.index_from"
-        }
-      });
+  return index_rec(s, l, i, c);
 }
 
 function index_from_opt(s, i, c) {
   let l = s.length;
-  if (!(i < 0 || i > l)) {
-    return index_rec_opt(s, l, i, c);
+  if (i < 0 || i > l) {
+    throw new Error("Invalid_argument", {
+          cause: {
+            RE_EXN_ID: "Invalid_argument",
+            _1: "String.index_from_opt / Bytes.index_from_opt"
+          }
+        });
   }
-  throw new Error("Invalid_argument", {
-        cause: {
-          RE_EXN_ID: "Invalid_argument",
-          _1: "String.index_from_opt / Bytes.index_from_opt"
-        }
-      });
+  return index_rec_opt(s, l, i, c);
 }
 
 function rindex_rec(s, _i, c) {
@@ -577,15 +576,15 @@ function rindex(s, c) {
 }
 
 function rindex_from(s, i, c) {
-  if (!(i < -1 || i >= s.length)) {
-    return rindex_rec(s, i, c);
+  if (i < -1 || i >= s.length) {
+    throw new Error("Invalid_argument", {
+          cause: {
+            RE_EXN_ID: "Invalid_argument",
+            _1: "String.rindex_from / Bytes.rindex_from"
+          }
+        });
   }
-  throw new Error("Invalid_argument", {
-        cause: {
-          RE_EXN_ID: "Invalid_argument",
-          _1: "String.rindex_from / Bytes.rindex_from"
-        }
-      });
+  return rindex_rec(s, i, c);
 }
 
 function rindex_rec_opt(s, _i, c) {
@@ -607,15 +606,15 @@ function rindex_opt(s, c) {
 }
 
 function rindex_from_opt(s, i, c) {
-  if (!(i < -1 || i >= s.length)) {
-    return rindex_rec_opt(s, i, c);
+  if (i < -1 || i >= s.length) {
+    throw new Error("Invalid_argument", {
+          cause: {
+            RE_EXN_ID: "Invalid_argument",
+            _1: "String.rindex_from_opt / Bytes.rindex_from_opt"
+          }
+        });
   }
-  throw new Error("Invalid_argument", {
-        cause: {
-          RE_EXN_ID: "Invalid_argument",
-          _1: "String.rindex_from_opt / Bytes.rindex_from_opt"
-        }
-      });
+  return rindex_rec_opt(s, i, c);
 }
 
 function contains_from(s, i, c) {
diff --git a/lib/js/caml.js b/lib/js/caml.js
index 15e8b80485..c3729dc091 100644
--- a/lib/js/caml.js
+++ b/lib/js/caml.js
@@ -166,10 +166,10 @@ function i64_le(x, y) {
 }
 
 function i64_min(x, y) {
-  if (i64_lt(x, y)) {
-    return x;
-  } else {
+  if (i64_ge(x, y)) {
     return y;
+  } else {
+    return x;
   }
 }
 
diff --git a/lib/js/char.js b/lib/js/char.js
index d4dd8308c7..2ae5bbaca9 100644
--- a/lib/js/char.js
+++ b/lib/js/char.js
@@ -3,15 +3,15 @@
 let Bytes = require("./bytes.js");
 
 function chr(n) {
-  if (!(n < 0 || n > 255)) {
-    return n;
+  if (n < 0 || n > 255) {
+    throw new Error("Invalid_argument", {
+          cause: {
+            RE_EXN_ID: "Invalid_argument",
+            _1: "Char.chr"
+          }
+        });
   }
-  throw new Error("Invalid_argument", {
-        cause: {
-          RE_EXN_ID: "Invalid_argument",
-          _1: "Char.chr"
-        }
-      });
+  return n;
 }
 
 function escaped(param) {
diff --git a/lib/js/digest.js b/lib/js/digest.js
index d62b9b57a8..51307ddf23 100644
--- a/lib/js/digest.js
+++ b/lib/js/digest.js
@@ -16,15 +16,15 @@ function bytes(b) {
 }
 
 function substring(str, ofs, len) {
-  if (!(ofs < 0 || len < 0 || ofs > (str.length - len | 0))) {
-    return Caml_md5.md5_string(str, ofs, len);
+  if (ofs < 0 || len < 0 || ofs > (str.length - len | 0)) {
+    throw new Error("Invalid_argument", {
+          cause: {
+            RE_EXN_ID: "Invalid_argument",
+            _1: "Digest.substring"
+          }
+        });
   }
-  throw new Error("Invalid_argument", {
-        cause: {
-          RE_EXN_ID: "Invalid_argument",
-          _1: "Digest.substring"
-        }
-      });
+  return Caml_md5.md5_string(str, ofs, len);
 }
 
 function subbytes(b, ofs, len) {
diff --git a/lib/js/filename.js b/lib/js/filename.js
index 8b1245ba55..530e6fe8cf 100644
--- a/lib/js/filename.js
+++ b/lib/js/filename.js
@@ -1,6 +1,7 @@
 'use strict';
 
 let Sys = require("./sys.js");
+let Bytes = require("./bytes.js");
 let Buffer = require("./buffer.js");
 let $$String = require("./string.js");
 let Caml_sys = require("./caml_sys.js");
@@ -193,7 +194,7 @@ function check_suffix$1(name, suff) {
     return false;
   }
   let s = $$String.sub(name, name.length - suff.length | 0, suff.length);
-  return $$String.lowercase_ascii(s) === $$String.lowercase_ascii(suff);
+  return Bytes.unsafe_to_string(Bytes.lowercase_ascii(Bytes.unsafe_of_string(s))) === Bytes.unsafe_to_string(Bytes.lowercase_ascii(Bytes.unsafe_of_string(suff)));
 }
 
 let temp_dir_name$1;
@@ -382,15 +383,15 @@ function concat(dirname, filename) {
 
 function chop_suffix(name, suff) {
   let n = name.length - suff.length | 0;
-  if (n >= 0) {
-    return $$String.sub(name, 0, n);
+  if (n < 0) {
+    throw new Error("Invalid_argument", {
+          cause: {
+            RE_EXN_ID: "Invalid_argument",
+            _1: "Filename.chop_suffix"
+          }
+        });
   }
-  throw new Error("Invalid_argument", {
-        cause: {
-          RE_EXN_ID: "Invalid_argument",
-          _1: "Filename.chop_suffix"
-        }
-      });
+  return $$String.sub(name, 0, n);
 }
 
 function extension_len(name) {
@@ -430,15 +431,15 @@ function extension(name) {
 
 function chop_extension(name) {
   let l = extension_len(name);
-  if (l !== 0) {
-    return $$String.sub(name, 0, name.length - l | 0);
+  if (l === 0) {
+    throw new Error("Invalid_argument", {
+          cause: {
+            RE_EXN_ID: "Invalid_argument",
+            _1: "Filename.chop_extension"
+          }
+        });
   }
-  throw new Error("Invalid_argument", {
-        cause: {
-          RE_EXN_ID: "Invalid_argument",
-          _1: "Filename.chop_extension"
-        }
-      });
+  return $$String.sub(name, 0, name.length - l | 0);
 }
 
 function remove_extension(name) {
diff --git a/lib/js/genlex.js b/lib/js/genlex.js
index d7603a2256..55f524893e 100644
--- a/lib/js/genlex.js
+++ b/lib/js/genlex.js
@@ -105,8 +105,8 @@ function make_lexer(keywords) {
               case 13 :
               case 26 :
               case 32 :
-                  exit = 2;
-                  break;
+                  Stream.junk(strm__);
+                  continue;
               case 34 :
                   Stream.junk(strm__);
                   reset_buffer();
@@ -175,10 +175,11 @@ function make_lexer(keywords) {
                     store(/* '-' */45);
                     store(c$2);
                     return number(strm__);
+                  } else {
+                    reset_buffer();
+                    store(/* '-' */45);
+                    return ident2(strm__);
                   }
-                  reset_buffer();
-                  store(/* '-' */45);
-                  return ident2(strm__);
               case 48 :
               case 49 :
               case 50 :
@@ -189,7 +190,7 @@ function make_lexer(keywords) {
               case 55 :
               case 56 :
               case 57 :
-                  exit = 5;
+                  exit = 4;
                   break;
               case 0 :
               case 1 :
@@ -238,7 +239,7 @@ function make_lexer(keywords) {
               case 62 :
               case 63 :
               case 64 :
-                  exit = 4;
+                  exit = 3;
                   break;
               
             }
@@ -247,7 +248,7 @@ function make_lexer(keywords) {
           switch (c) {
             case 92 :
             case 94 :
-                exit = 4;
+                exit = 3;
                 break;
             case 91 :
             case 93 :
@@ -255,14 +256,14 @@ function make_lexer(keywords) {
                 exit = 1;
                 break;
             default:
-              exit = 3;
+              exit = 2;
           }
         }
       } else {
         exit = c >= 127 ? (
-            c > 255 || c < 192 ? 1 : 3
+            c > 255 || c < 192 ? 1 : 2
           ) : (
-            c !== 125 ? 4 : 1
+            c !== 125 ? 3 : 1
           );
       }
       switch (exit) {
@@ -270,49 +271,42 @@ function make_lexer(keywords) {
             Stream.junk(strm__);
             return keyword_or_error(c);
         case 2 :
-            Stream.junk(strm__);
-            continue;
-        case 3 :
             Stream.junk(strm__);
             reset_buffer();
             store(c);
             while(true) {
               let c$3 = Stream.peek(strm__);
-              if (c$3 !== undefined) {
-                let exit$1 = 0;
-                if (c$3 >= 91) {
-                  if (c$3 > 122 || c$3 < 95) {
-                    if (!(c$3 > 255 || c$3 < 192)) {
-                      exit$1 = 2;
-                    }
-                    
-                  } else if (c$3 !== 96) {
-                    exit$1 = 2;
-                  }
-                  
-                } else if (c$3 >= 48) {
-                  if (c$3 > 64 || c$3 < 58) {
-                    exit$1 = 2;
+              if (c$3 === undefined) {
+                return ident_or_keyword(get_string());
+              }
+              if (c$3 >= 91) {
+                if (c$3 > 122 || c$3 < 95) {
+                  if (c$3 > 255 || c$3 < 192) {
+                    return ident_or_keyword(get_string());
                   }
                   
-                } else if (c$3 === 39) {
-                  exit$1 = 2;
+                } else if (c$3 === 96) {
+                  return ident_or_keyword(get_string());
                 }
-                if (exit$1 === 2) {
-                  Stream.junk(strm__);
-                  store(c$3);
-                  continue;
+                
+              } else if (c$3 >= 48) {
+                if (!(c$3 > 64 || c$3 < 58)) {
+                  return ident_or_keyword(get_string());
                 }
                 
+              } else if (c$3 !== 39) {
+                return ident_or_keyword(get_string());
               }
-              return ident_or_keyword(get_string());
+              Stream.junk(strm__);
+              store(c$3);
+              continue;
             };
-        case 4 :
+        case 3 :
             Stream.junk(strm__);
             reset_buffer();
             store(c);
             return ident2(strm__);
-        case 5 :
+        case 4 :
             Stream.junk(strm__);
             reset_buffer();
             store(c);
@@ -324,81 +318,80 @@ function make_lexer(keywords) {
   let ident2 = function (strm__) {
     while(true) {
       let c = Stream.peek(strm__);
-      if (c !== undefined) {
-        let exit = 0;
-        if (c >= 94) {
-          if (c > 125 || c < 95) {
-            if (c < 127) {
-              exit = 2;
-            }
-            
-          } else if (c === 124) {
-            exit = 2;
-          }
-          
-        } else if (c >= 65) {
-          if (c === 92) {
-            exit = 2;
+      if (c === undefined) {
+        return ident_or_keyword(get_string());
+      }
+      if (c >= 94) {
+        if (c > 125 || c < 95) {
+          if (c >= 127) {
+            return ident_or_keyword(get_string());
           }
           
-        } else if (c >= 33) {
-          switch (c) {
-            case 34 :
-            case 39 :
-            case 40 :
-            case 41 :
-            case 44 :
-            case 46 :
-            case 48 :
-            case 49 :
-            case 50 :
-            case 51 :
-            case 52 :
-            case 53 :
-            case 54 :
-            case 55 :
-            case 56 :
-            case 57 :
-            case 59 :
-                break;
-            case 33 :
-            case 35 :
-            case 36 :
-            case 37 :
-            case 38 :
-            case 42 :
-            case 43 :
-            case 45 :
-            case 47 :
-            case 58 :
-            case 60 :
-            case 61 :
-            case 62 :
-            case 63 :
-            case 64 :
-                exit = 2;
-                break;
-            
-          }
+        } else if (c !== 124) {
+          return ident_or_keyword(get_string());
         }
-        if (exit === 2) {
-          Stream.junk(strm__);
-          store(c);
-          continue;
+        
+      } else if (c >= 65) {
+        if (c !== 92) {
+          return ident_or_keyword(get_string());
         }
         
+      } else {
+        if (c < 33) {
+          return ident_or_keyword(get_string());
+        }
+        switch (c) {
+          case 34 :
+          case 39 :
+          case 40 :
+          case 41 :
+          case 44 :
+          case 46 :
+          case 48 :
+          case 49 :
+          case 50 :
+          case 51 :
+          case 52 :
+          case 53 :
+          case 54 :
+          case 55 :
+          case 56 :
+          case 57 :
+          case 59 :
+              return ident_or_keyword(get_string());
+          case 33 :
+          case 35 :
+          case 36 :
+          case 37 :
+          case 38 :
+          case 42 :
+          case 43 :
+          case 45 :
+          case 47 :
+          case 58 :
+          case 60 :
+          case 61 :
+          case 62 :
+          case 63 :
+          case 64 :
+              break;
+          
+        }
       }
-      return ident_or_keyword(get_string());
+      Stream.junk(strm__);
+      store(c);
+      continue;
     };
   };
   let number = function (strm__) {
     while(true) {
       let c = Stream.peek(strm__);
       if (c !== undefined) {
-        let exit = 0;
         if (c >= 58) {
           if (!(c !== 69 && c !== 101)) {
-            exit = 2;
+            Stream.junk(strm__);
+            store(/* 'E' */69);
+            return exponent_part(strm__);
           }
           
         } else if (c !== 46) {
@@ -434,12 +427,6 @@ function make_lexer(keywords) {
             };
           };
         }
-        if (exit === 2) {
-          Stream.junk(strm__);
-          store(/* 'E' */69);
-          return exponent_part(strm__);
-        }
-        
       }
       return {
         TAG: "Int",
@@ -449,15 +436,13 @@ function make_lexer(keywords) {
   };
   let exponent_part = function (strm__) {
     let c = Stream.peek(strm__);
-    if (c === undefined) {
+    if (c !== undefined && !(c !== 43 && c !== 45)) {
+      Stream.junk(strm__);
+      store(c);
       return end_exponent_part(strm__);
-    }
-    if (c !== 43 && c !== 45) {
+    } else {
       return end_exponent_part(strm__);
     }
-    Stream.junk(strm__);
-    store(c);
-    return end_exponent_part(strm__);
   };
   let end_exponent_part = function (strm__) {
     while(true) {
@@ -690,4 +675,4 @@ function make_lexer(keywords) {
 }
 
 exports.make_lexer = make_lexer;
-/* Hashtbl Not a pure module */
+/* No side effect */
diff --git a/lib/js/hashtbl.js b/lib/js/hashtbl.js
index e06bff9294..e882bc97c2 100644
--- a/lib/js/hashtbl.js
+++ b/lib/js/hashtbl.js
@@ -1,7 +1,6 @@
 'use strict';
 
 let Caml = require("./caml.js");
-let Lazy = require("./lazy.js");
 let $$Array = require("./array.js");
 let Random = require("./random.js");
 let Caml_obj = require("./caml_obj.js");
@@ -39,7 +38,7 @@ function is_randomized() {
   return randomized.contents;
 }
 
-let prng = Lazy.from_fun(function () {
+let prng = CamlinternalLazy.from_fun(function () {
   return Random.State.make_self_init();
 });
 
@@ -1140,4 +1139,4 @@ exports.hash = hash;
 exports.seeded_hash = seeded_hash;
 exports.hash_param = hash_param;
 exports.seeded_hash_param = seeded_hash_param;
-/* prng Not a pure module */
+/* No side effect */
diff --git a/lib/js/hashtblLabels.js b/lib/js/hashtblLabels.js
index 57c37b4f41..6aa7894bbb 100644
--- a/lib/js/hashtblLabels.js
+++ b/lib/js/hashtblLabels.js
@@ -194,4 +194,4 @@ exports.filter_map_inplace = filter_map_inplace;
 exports.fold = fold;
 exports.MakeSeeded = MakeSeeded;
 exports.Make = Make;
-/* Hashtbl Not a pure module */
+/* No side effect */
diff --git a/lib/js/js.js b/lib/js/js.js
index 78030e36c4..de368b57e7 100644
--- a/lib/js/js.js
+++ b/lib/js/js.js
@@ -1,8 +1,6 @@
 'use strict';
 
 
-let Internal = {};
-
 let Null;
 
 let Undefined;
@@ -69,7 +67,6 @@ let $$Map;
 
 let $$WeakMap;
 
-exports.Internal = Internal;
 exports.Null = Null;
 exports.Undefined = Undefined;
 exports.Nullable = Nullable;
diff --git a/lib/js/lazy.js b/lib/js/lazy.js
index 30aefe8c5e..fe1b4b9d8b 100644
--- a/lib/js/lazy.js
+++ b/lib/js/lazy.js
@@ -8,9 +8,7 @@ function from_fun(f) {
   });
 }
 
-function from_val(v) {
-  return CamlinternalLazy.from_val(v);
-}
+let from_val = CamlinternalLazy.from_val;
 
 let Undefined = CamlinternalLazy.Undefined;
 
diff --git a/lib/js/list.js b/lib/js/list.js
index 436c025ee2..033c5376c2 100644
--- a/lib/js/list.js
+++ b/lib/js/list.js
@@ -155,19 +155,19 @@ function init_aux(i, n, f) {
 }
 
 function init(len, f) {
-  if (len >= 0) {
-    if (len > 10000) {
-      return rev_append(init_tailrec_aux(/* [] */0, 0, len, f), /* [] */0);
-    } else {
-      return init_aux(0, len, f);
-    }
+  if (len < 0) {
+    throw new Error("Invalid_argument", {
+          cause: {
+            RE_EXN_ID: "Invalid_argument",
+            _1: "List.init"
+          }
+        });
+  }
+  if (len > 10000) {
+    return rev_append(init_tailrec_aux(/* [] */0, 0, len, f), /* [] */0);
+  } else {
+    return init_aux(0, len, f);
   }
-  throw new Error("Invalid_argument", {
-        cause: {
-          RE_EXN_ID: "Invalid_argument",
-          _1: "List.init"
-        }
-      });
 }
 
 function flatten(param) {
@@ -323,15 +323,15 @@ function rev_map2(f, l1, l2) {
             }
           });
     }
-    if (!l2$1) {
-      return accu;
+    if (l2$1) {
+      throw new Error("Invalid_argument", {
+            cause: {
+              RE_EXN_ID: "Invalid_argument",
+              _1: "List.rev_map2"
+            }
+          });
     }
-    throw new Error("Invalid_argument", {
-          cause: {
-            RE_EXN_ID: "Invalid_argument",
-            _1: "List.rev_map2"
-          }
-        });
+    return accu;
   };
 }
 
@@ -384,15 +384,15 @@ function fold_left2(f, _accu, _l1, _l2) {
             }
           });
     }
-    if (!l2) {
-      return accu;
+    if (l2) {
+      throw new Error("Invalid_argument", {
+            cause: {
+              RE_EXN_ID: "Invalid_argument",
+              _1: "List.fold_left2"
+            }
+          });
     }
-    throw new Error("Invalid_argument", {
-          cause: {
-            RE_EXN_ID: "Invalid_argument",
-            _1: "List.fold_left2"
-          }
-        });
+    return accu;
   };
 }
 
@@ -408,15 +408,15 @@ function fold_right2(f, l1, l2, accu) {
           }
         });
   }
-  if (!l2) {
-    return accu;
+  if (l2) {
+    throw new Error("Invalid_argument", {
+          cause: {
+            RE_EXN_ID: "Invalid_argument",
+            _1: "List.fold_right2"
+          }
+        });
   }
-  throw new Error("Invalid_argument", {
-        cause: {
-          RE_EXN_ID: "Invalid_argument",
-          _1: "List.fold_right2"
-        }
-      });
+  return accu;
 }
 
 function for_all(p, _param) {
diff --git a/lib/js/listLabels.js b/lib/js/listLabels.js
index 6f81e7afde..287a2c0f3a 100644
--- a/lib/js/listLabels.js
+++ b/lib/js/listLabels.js
@@ -155,19 +155,19 @@ function init_aux(i, n, f) {
 }
 
 function init(len, f) {
-  if (len >= 0) {
-    if (len > 10000) {
-      return rev_append(init_tailrec_aux(/* [] */0, 0, len, f), /* [] */0);
-    } else {
-      return init_aux(0, len, f);
-    }
+  if (len < 0) {
+    throw new Error("Invalid_argument", {
+          cause: {
+            RE_EXN_ID: "Invalid_argument",
+            _1: "List.init"
+          }
+        });
+  }
+  if (len > 10000) {
+    return rev_append(init_tailrec_aux(/* [] */0, 0, len, f), /* [] */0);
+  } else {
+    return init_aux(0, len, f);
   }
-  throw new Error("Invalid_argument", {
-        cause: {
-          RE_EXN_ID: "Invalid_argument",
-          _1: "List.init"
-        }
-      });
 }
 
 function flatten(param) {
@@ -323,15 +323,15 @@ function rev_map2(f, l1, l2) {
             }
           });
     }
-    if (!l2$1) {
-      return accu;
+    if (l2$1) {
+      throw new Error("Invalid_argument", {
+            cause: {
+              RE_EXN_ID: "Invalid_argument",
+              _1: "List.rev_map2"
+            }
+          });
     }
-    throw new Error("Invalid_argument", {
-          cause: {
-            RE_EXN_ID: "Invalid_argument",
-            _1: "List.rev_map2"
-          }
-        });
+    return accu;
   };
 }
 
@@ -384,15 +384,15 @@ function fold_left2(f, _accu, _l1, _l2) {
             }
           });
     }
-    if (!l2) {
-      return accu;
+    if (l2) {
+      throw new Error("Invalid_argument", {
+            cause: {
+              RE_EXN_ID: "Invalid_argument",
+              _1: "List.fold_left2"
+            }
+          });
     }
-    throw new Error("Invalid_argument", {
-          cause: {
-            RE_EXN_ID: "Invalid_argument",
-            _1: "List.fold_left2"
-          }
-        });
+    return accu;
   };
 }
 
@@ -408,15 +408,15 @@ function fold_right2(f, l1, l2, accu) {
           }
         });
   }
-  if (!l2) {
-    return accu;
+  if (l2) {
+    throw new Error("Invalid_argument", {
+          cause: {
+            RE_EXN_ID: "Invalid_argument",
+            _1: "List.fold_right2"
+          }
+        });
   }
-  throw new Error("Invalid_argument", {
-        cause: {
-          RE_EXN_ID: "Invalid_argument",
-          _1: "List.fold_right2"
-        }
-      });
+  return accu;
 }
 
 function for_all(p, _param) {
diff --git a/lib/js/moreLabels.js b/lib/js/moreLabels.js
index aec5317d26..baee384c01 100644
--- a/lib/js/moreLabels.js
+++ b/lib/js/moreLabels.js
@@ -1975,4 +1975,4 @@ let $$Set = {
 exports.Hashtbl = Hashtbl;
 exports.$$Map = $$Map;
 exports.$$Set = $$Set;
-/* HashtblLabels Not a pure module */
+/* No side effect */
diff --git a/lib/js/pervasives.js b/lib/js/pervasives.js
index 851b6b0782..f849b7806a 100644
--- a/lib/js/pervasives.js
+++ b/lib/js/pervasives.js
@@ -185,7 +185,7 @@ function print_int(i) {
 }
 
 function print_float(i) {
-  console.log(string_of_float(i));
+  console.log(valid_float_lexem(Caml_format.format_float("%.12g", i)));
 }
 
 function print_string(prim) {
diff --git a/lib/js/random.js b/lib/js/random.js
index 68552595f8..bf7a70c1b7 100644
--- a/lib/js/random.js
+++ b/lib/js/random.js
@@ -74,65 +74,65 @@ function bits(s) {
 }
 
 function int(s, bound) {
-  if (!(bound > 1073741823 || bound <= 0)) {
-    while(true) {
-      let r = bits(s);
-      let v = r % bound;
-      if ((r - v | 0) <= ((1073741823 - bound | 0) + 1 | 0)) {
-        return v;
-      }
-      continue;
-    };
+  if (bound > 1073741823 || bound <= 0) {
+    throw new Error("Invalid_argument", {
+          cause: {
+            RE_EXN_ID: "Invalid_argument",
+            _1: "Random.int"
+          }
+        });
   }
-  throw new Error("Invalid_argument", {
-        cause: {
-          RE_EXN_ID: "Invalid_argument",
-          _1: "Random.int"
-        }
-      });
+  while(true) {
+    let r = bits(s);
+    let v = r % bound;
+    if ((r - v | 0) <= ((1073741823 - bound | 0) + 1 | 0)) {
+      return v;
+    }
+    continue;
+  };
 }
 
 function int32(s, bound) {
-  if (bound > 0) {
-    while(true) {
-      let b1 = bits(s);
-      let b2 = ((bits(s) & 1) << 30);
-      let r = b1 | b2;
-      let v = r % bound;
-      if ((r - v | 0) <= ((Int32.max_int - bound | 0) + 1 | 0)) {
-        return v;
-      }
-      continue;
-    };
+  if (bound <= 0) {
+    throw new Error("Invalid_argument", {
+          cause: {
+            RE_EXN_ID: "Invalid_argument",
+            _1: "Random.int32"
+          }
+        });
   }
-  throw new Error("Invalid_argument", {
-        cause: {
-          RE_EXN_ID: "Invalid_argument",
-          _1: "Random.int32"
-        }
-      });
+  while(true) {
+    let b1 = bits(s);
+    let b2 = ((bits(s) & 1) << 30);
+    let r = b1 | b2;
+    let v = r % bound;
+    if ((r - v | 0) <= ((Int32.max_int - bound | 0) + 1 | 0)) {
+      return v;
+    }
+    continue;
+  };
 }
 
 function int64(s, bound) {
-  if (!Caml.i64_le(bound, Caml_int64.zero)) {
-    while(true) {
-      let b1 = Caml_int64.of_int32(bits(s));
-      let b2 = Caml_int64.lsl_(Caml_int64.of_int32(bits(s)), 30);
-      let b3 = Caml_int64.lsl_(Caml_int64.of_int32(bits(s) & 7), 60);
-      let r = Caml_int64.or_(b1, Caml_int64.or_(b2, b3));
-      let v = Caml_int64.mod_(r, bound);
-      if (!Caml.i64_gt(Caml_int64.sub(r, v), Caml_int64.add(Caml_int64.sub(Int64.max_int, bound), Caml_int64.one))) {
-        return v;
-      }
-      continue;
-    };
+  if (Caml.i64_le(bound, Caml_int64.zero)) {
+    throw new Error("Invalid_argument", {
+          cause: {
+            RE_EXN_ID: "Invalid_argument",
+            _1: "Random.int64"
+          }
+        });
   }
-  throw new Error("Invalid_argument", {
-        cause: {
-          RE_EXN_ID: "Invalid_argument",
-          _1: "Random.int64"
-        }
-      });
+  while(true) {
+    let b1 = Caml_int64.of_int32(bits(s));
+    let b2 = Caml_int64.lsl_(Caml_int64.of_int32(bits(s)), 30);
+    let b3 = Caml_int64.lsl_(Caml_int64.of_int32(bits(s) & 7), 60);
+    let r = Caml_int64.or_(b1, Caml_int64.or_(b2, b3));
+    let v = Caml_int64.mod_(r, bound);
+    if (!Caml.i64_gt(Caml_int64.sub(r, v), Caml_int64.add(Caml_int64.sub(Int64.max_int, bound), Caml_int64.one))) {
+      return v;
+    }
+    continue;
+  };
 }
 
 function rawfloat(s) {
@@ -227,7 +227,7 @@ function int64$1(bound) {
 }
 
 function float$1(scale) {
-  return float($$default, scale);
+  return rawfloat($$default) * scale;
 }
 
 function bool$1() {
diff --git a/lib/js/stream.js b/lib/js/stream.js
index 8912267e9e..2ee0c6b4be 100644
--- a/lib/js/stream.js
+++ b/lib/js/stream.js
@@ -1,6 +1,5 @@
 'use strict';
 
-let Lazy = require("./lazy.js");
 let List = require("./list.js");
 let Caml_bytes = require("./caml_bytes.js");
 let Caml_option = require("./caml_option.js");
@@ -362,32 +361,38 @@ function ising(i) {
 }
 
 function lapp(f, s) {
+  let f$1 = function () {
+    return {
+      TAG: "Sapp",
+      _0: data(f()),
+      _1: data(s)
+    };
+  };
   return {
     count: 0,
     data: {
       TAG: "Slazy",
-      _0: Lazy.from_fun(function () {
-        return {
-          TAG: "Sapp",
-          _0: data(f()),
-          _1: data(s)
-        };
+      _0: CamlinternalLazy.from_fun(function () {
+        return f$1();
       })
     }
   };
 }
 
 function lcons(f, s) {
+  let f$1 = function () {
+    return {
+      TAG: "Scons",
+      _0: f(),
+      _1: data(s)
+    };
+  };
   return {
     count: 0,
     data: {
       TAG: "Slazy",
-      _0: Lazy.from_fun(function () {
-        return {
-          TAG: "Scons",
-          _0: f(),
-          _1: data(s)
-        };
+      _0: CamlinternalLazy.from_fun(function () {
+        return f$1();
       })
     }
   };
@@ -398,7 +403,7 @@ function lsing(f) {
     count: 0,
     data: {
       TAG: "Slazy",
-      _0: Lazy.from_fun(function () {
+      _0: CamlinternalLazy.from_fun(function () {
         return {
           TAG: "Scons",
           _0: f(),
@@ -414,7 +419,7 @@ function slazy(f) {
     count: 0,
     data: {
       TAG: "Slazy",
-      _0: Lazy.from_fun(function () {
+      _0: CamlinternalLazy.from_fun(function () {
         return data(f());
       })
     }
diff --git a/lib/js/string.js b/lib/js/string.js
index 75ba5054f7..e26e35272b 100644
--- a/lib/js/string.js
+++ b/lib/js/string.js
@@ -128,28 +128,28 @@ function index_opt(s, c) {
 
 function index_from(s, i, c) {
   let l = s.length;
-  if (!(i < 0 || i > l)) {
-    return index_rec(s, l, i, c);
+  if (i < 0 || i > l) {
+    throw new Error("Invalid_argument", {
+          cause: {
+            RE_EXN_ID: "Invalid_argument",
+            _1: "String.index_from / Bytes.index_from"
+          }
+        });
   }
-  throw new Error("Invalid_argument", {
-        cause: {
-          RE_EXN_ID: "Invalid_argument",
-          _1: "String.index_from / Bytes.index_from"
-        }
-      });
+  return index_rec(s, l, i, c);
 }
 
 function index_from_opt(s, i, c) {
   let l = s.length;
-  if (!(i < 0 || i > l)) {
-    return index_rec_opt(s, l, i, c);
+  if (i < 0 || i > l) {
+    throw new Error("Invalid_argument", {
+          cause: {
+            RE_EXN_ID: "Invalid_argument",
+            _1: "String.index_from_opt / Bytes.index_from_opt"
+          }
+        });
   }
-  throw new Error("Invalid_argument", {
-        cause: {
-          RE_EXN_ID: "Invalid_argument",
-          _1: "String.index_from_opt / Bytes.index_from_opt"
-        }
-      });
+  return index_rec_opt(s, l, i, c);
 }
 
 function rindex_rec(s, _i, c) {
@@ -175,15 +175,15 @@ function rindex(s, c) {
 }
 
 function rindex_from(s, i, c) {
-  if (!(i < -1 || i >= s.length)) {
-    return rindex_rec(s, i, c);
+  if (i < -1 || i >= s.length) {
+    throw new Error("Invalid_argument", {
+          cause: {
+            RE_EXN_ID: "Invalid_argument",
+            _1: "String.rindex_from / Bytes.rindex_from"
+          }
+        });
   }
-  throw new Error("Invalid_argument", {
-        cause: {
-          RE_EXN_ID: "Invalid_argument",
-          _1: "String.rindex_from / Bytes.rindex_from"
-        }
-      });
+  return rindex_rec(s, i, c);
 }
 
 function rindex_rec_opt(s, _i, c) {
@@ -205,15 +205,15 @@ function rindex_opt(s, c) {
 }
 
 function rindex_from_opt(s, i, c) {
-  if (!(i < -1 || i >= s.length)) {
-    return rindex_rec_opt(s, i, c);
+  if (i < -1 || i >= s.length) {
+    throw new Error("Invalid_argument", {
+          cause: {
+            RE_EXN_ID: "Invalid_argument",
+            _1: "String.rindex_from_opt / Bytes.rindex_from_opt"
+          }
+        });
   }
-  throw new Error("Invalid_argument", {
-        cause: {
-          RE_EXN_ID: "Invalid_argument",
-          _1: "String.rindex_from_opt / Bytes.rindex_from_opt"
-        }
-      });
+  return rindex_rec_opt(s, i, c);
 }
 
 function contains_from(s, i, c) {
diff --git a/lib/js/stringLabels.js b/lib/js/stringLabels.js
index af81310fe7..66077dc73c 100644
--- a/lib/js/stringLabels.js
+++ b/lib/js/stringLabels.js
@@ -14,9 +14,7 @@ function sub(s, ofs, len) {
   return Bytes.unsafe_to_string(Bytes.sub(Bytes.unsafe_of_string(s), ofs, len));
 }
 
-function blit(src, src_pos, dst, dst_pos, len) {
-  Bytes.blit_string(src, src_pos, dst, dst_pos, len);
-}
+let blit = Bytes.blit_string;
 
 function concat(sep, xs) {
   return $$Array.of_list(xs).join(sep);
@@ -132,28 +130,28 @@ function index_opt(s, c) {
 
 function index_from(s, i, c) {
   let l = s.length;
-  if (!(i < 0 || i > l)) {
-    return index_rec(s, l, i, c);
+  if (i < 0 || i > l) {
+    throw new Error("Invalid_argument", {
+          cause: {
+            RE_EXN_ID: "Invalid_argument",
+            _1: "String.index_from / Bytes.index_from"
+          }
+        });
   }
-  throw new Error("Invalid_argument", {
-        cause: {
-          RE_EXN_ID: "Invalid_argument",
-          _1: "String.index_from / Bytes.index_from"
-        }
-      });
+  return index_rec(s, l, i, c);
 }
 
 function index_from_opt(s, i, c) {
   let l = s.length;
-  if (!(i < 0 || i > l)) {
-    return index_rec_opt(s, l, i, c);
+  if (i < 0 || i > l) {
+    throw new Error("Invalid_argument", {
+          cause: {
+            RE_EXN_ID: "Invalid_argument",
+            _1: "String.index_from_opt / Bytes.index_from_opt"
+          }
+        });
   }
-  throw new Error("Invalid_argument", {
-        cause: {
-          RE_EXN_ID: "Invalid_argument",
-          _1: "String.index_from_opt / Bytes.index_from_opt"
-        }
-      });
+  return index_rec_opt(s, l, i, c);
 }
 
 function rindex_rec(s, _i, c) {
@@ -179,15 +177,15 @@ function rindex(s, c) {
 }
 
 function rindex_from(s, i, c) {
-  if (!(i < -1 || i >= s.length)) {
-    return rindex_rec(s, i, c);
+  if (i < -1 || i >= s.length) {
+    throw new Error("Invalid_argument", {
+          cause: {
+            RE_EXN_ID: "Invalid_argument",
+            _1: "String.rindex_from / Bytes.rindex_from"
+          }
+        });
   }
-  throw new Error("Invalid_argument", {
-        cause: {
-          RE_EXN_ID: "Invalid_argument",
-          _1: "String.rindex_from / Bytes.rindex_from"
-        }
-      });
+  return rindex_rec(s, i, c);
 }
 
 function rindex_rec_opt(s, _i, c) {
@@ -209,15 +207,15 @@ function rindex_opt(s, c) {
 }
 
 function rindex_from_opt(s, i, c) {
-  if (!(i < -1 || i >= s.length)) {
-    return rindex_rec_opt(s, i, c);
+  if (i < -1 || i >= s.length) {
+    throw new Error("Invalid_argument", {
+          cause: {
+            RE_EXN_ID: "Invalid_argument",
+            _1: "String.rindex_from_opt / Bytes.rindex_from_opt"
+          }
+        });
   }
-  throw new Error("Invalid_argument", {
-        cause: {
-          RE_EXN_ID: "Invalid_argument",
-          _1: "String.rindex_from_opt / Bytes.rindex_from_opt"
-        }
-      });
+  return rindex_rec_opt(s, i, c);
 }
 
 function contains_from(s, i, c) {
diff --git a/lib/js/sys.js b/lib/js/sys.js
index 8239622f87..48a03282b9 100644
--- a/lib/js/sys.js
+++ b/lib/js/sys.js
@@ -45,20 +45,7 @@ function set_signal(sig_num, sig_beh) {
 let Break = /* @__PURE__ */Caml_exceptions.create("Sys.Break");
 
 function catch_break(on) {
-  if (on) {
-    return set_signal(-6, {
-      TAG: "Signal_handle",
-      _0: (function (param) {
-        throw new Error(Break, {
-              cause: {
-                RE_EXN_ID: Break
-              }
-            });
-      })
-    });
-  } else {
-    return set_signal(-6, "Signal_default");
-  }
+  
 }
 
 function enable_runtime_warnings(param) {
diff --git a/lib/js/uchar.js b/lib/js/uchar.js
index 27e3a6e7ac..87523c8fb6 100644
--- a/lib/js/uchar.js
+++ b/lib/js/uchar.js
@@ -15,30 +15,30 @@ function succ(u) {
   if (u === 55295) {
     return 57344;
   }
-  if (u !== 1114111) {
-    return u + 1 | 0;
+  if (u === 1114111) {
+    throw new Error("Invalid_argument", {
+          cause: {
+            RE_EXN_ID: "Invalid_argument",
+            _1: "U+10FFFF has no successor"
+          }
+        });
   }
-  throw new Error("Invalid_argument", {
-        cause: {
-          RE_EXN_ID: "Invalid_argument",
-          _1: "U+10FFFF has no successor"
-        }
-      });
+  return u + 1 | 0;
 }
 
 function pred(u) {
   if (u === 57344) {
     return 55295;
   }
-  if (u !== 0) {
-    return u - 1 | 0;
+  if (u === 0) {
+    throw new Error("Invalid_argument", {
+          cause: {
+            RE_EXN_ID: "Invalid_argument",
+            _1: "U+0000 has no predecessor"
+          }
+        });
   }
-  throw new Error("Invalid_argument", {
-        cause: {
-          RE_EXN_ID: "Invalid_argument",
-          _1: "U+0000 has no predecessor"
-        }
-      });
+  return u - 1 | 0;
 }
 
 function is_valid(i) {