Merge pull request #1775 from dotty-staging/add-implicit-funtypes

Add implicit function types

Author: odersky

compiler/src/dotty/tools/backend/jvm/DottyBackendInterface.scala

@@ -39,6 +39,10 @@ import dotty.tools.dotc.core.Names.TypeName
 import scala.annotation.tailrec
 
 class DottyBackendInterface(outputDirectory: AbstractFile, val superCallsMap: Map[Symbol, Set[ClassSymbol]])(implicit ctx: Context) extends BackendInterface{
+  import Symbols.{toDenot, toClassDenot}
+    // Dotty deviation: Need to (re-)import implicit decorators here because otherwise
+    // they would be shadowed by the more deeply nested `symHelper` decorator.
+
   type Symbol          = Symbols.Symbol
   type Type            = Types.Type
   type Tree            = tpd.Tree
@@ -683,8 +687,6 @@ class DottyBackendInterface(outputDirectory: AbstractFile, val superCallsMap: Ma
       else sym.enclosingClass(ctx.withPhase(ctx.flattenPhase.prev))
     } //todo is handled specially for JavaDefined symbols in scalac
 
-
-
     // members
     def primaryConstructor: Symbol = toDenot(sym).primaryConstructor
 

compiler/src/dotty/tools/dotc/Compiler.scala

@@ -61,6 +61,7 @@ class Compiler {
            new PatternMatcher,      // Compile pattern matches
            new ExplicitOuter,       // Add accessors to outer classes from nested ones.
            new ExplicitSelf,        // Make references to non-trivial self types explicit as casts
+           new ShortcutImplicits,   // Allow implicit functions without creating closures
            new CrossCastAnd,        // Normalize selections involving intersection types.
            new Splitter),           // Expand selections involving union types into conditionals
       List(new VCInlineMethods,     // Inlines calls to value class methods

compiler/src/dotty/tools/dotc/ast/Desugar.scala

@@ -123,6 +123,13 @@ object desugar {
     else vdef
   }
 
+  def makeImplicitParameters(tpts: List[Tree], forPrimaryConstructor: Boolean)(implicit ctx: Context) =
+    for (tpt <- tpts) yield {
+       val paramFlags: FlagSet = if (forPrimaryConstructor) PrivateLocalParamAccessor else Param
+       val epname = ctx.freshName(nme.EVIDENCE_PARAM_PREFIX).toTermName
+       ValDef(epname, tpt, EmptyTree).withFlags(paramFlags | Implicit)
+    }
+
   /** Expand context bounds to evidence params. E.g.,
    *
    *      def f[T >: L <: H : B](params)
@@ -143,19 +150,16 @@ object desugar {
     val epbuf = new ListBuffer[ValDef]
     def desugarContextBounds(rhs: Tree): Tree = rhs match {
       case ContextBounds(tbounds, cxbounds) =>
-        for (cxbound <- cxbounds) {
-          val paramFlags: FlagSet = if (isPrimaryConstructor) PrivateLocalParamAccessor else Param
-          val epname = ctx.freshName(nme.EVIDENCE_PARAM_PREFIX).toTermName
-          epbuf += ValDef(epname, cxbound, EmptyTree).withFlags(paramFlags | Implicit)
-        }
+        for (cxbound <- cxbounds)
+          epbuf ++= makeImplicitParameters(cxbounds, isPrimaryConstructor)
         tbounds
       case PolyTypeTree(tparams, body) =>
         cpy.PolyTypeTree(rhs)(tparams, desugarContextBounds(body))
       case _ =>
         rhs
     }
-    val tparams1 = tparams mapConserve { tdef =>
-      cpy.TypeDef(tdef)(rhs = desugarContextBounds(tdef.rhs))
+    val tparams1 = tparams mapConserve { tparam =>
+      cpy.TypeDef(tparam)(rhs = desugarContextBounds(tparam.rhs))
     }
 
     val meth1 = addEvidenceParams(cpy.DefDef(meth)(tparams = tparams1), epbuf.toList)
@@ -680,6 +684,11 @@ object desugar {
     Function(param :: Nil, Block(vdefs, body))
   }
 
+  def makeImplicitFunction(formals: List[Type], body: Tree)(implicit ctx: Context): Tree = {
+    val params = makeImplicitParameters(formals.map(TypeTree), forPrimaryConstructor = false)
+    new ImplicitFunction(params, body)
+  }
+
   /** Add annotation with class `cls` to tree:
    *      tree @cls
    */

compiler/src/dotty/tools/dotc/ast/TreeInfo.scala

@@ -290,6 +290,16 @@ trait UntypedTreeInfo extends TreeInfo[Untyped] { self: Trees.Instance[Untyped]
     case _ => false
   }
 
+  /** Is `tree` an implicit function or closure, possibly nested in a block? */
+  def isImplicitClosure(tree: Tree)(implicit ctx: Context): Boolean = unsplice(tree) match {
+    case Function((param: untpd.ValDef) :: _, _) => param.mods.is(Implicit)
+    case Closure(_, meth, _) => true
+    case Block(Nil, expr) => isImplicitClosure(expr)
+    case Block(DefDef(nme.ANON_FUN, _, (param :: _) :: _, _, _) :: Nil, _: Closure) =>
+      param.mods.is(Implicit)
+    case _ => false
+  }
+
   // todo: fill with other methods from TreeInfo that only apply to untpd.Tree's
 }
 
@@ -501,7 +511,7 @@ trait TypedTreeInfo extends TreeInfo[Type] { self: Trees.Instance[Type] =>
    */
   object closure {
     def unapply(tree: Tree): Option[(List[Tree], Tree, Tree)] = tree match {
-      case Block(_, Closure(env, meth, tpt)) => Some(env, meth, tpt)
+      case Block(_, expr) => unapply(expr)
       case Closure(env, meth, tpt) => Some(env, meth, tpt)
       case _ => None
     }

compiler/src/dotty/tools/dotc/ast/Trees.scala

@@ -890,6 +890,11 @@ object Trees {
         case tree: Select if (qualifier eq tree.qualifier) && (name == tree.name) => tree
         case _ => finalize(tree, untpd.Select(qualifier, name))
       }
+      /** Copy Ident or Select trees */
+      def Ref(tree: RefTree)(name: Name)(implicit ctx: Context) = tree match {
+        case Ident(_) => Ident(tree)(name)
+        case Select(qual, _) => Select(tree)(qual, name)
+      }
       def This(tree: Tree)(qual: untpd.Ident): This = tree match {
         case tree: This if qual eq tree.qual => tree
         case _ => finalize(tree, untpd.This(qual))

compiler/src/dotty/tools/dotc/ast/tpd.scala

@@ -450,7 +450,8 @@ object tpd extends Trees.Instance[Type] with TypedTreeInfo {
       } else foldOver(sym, tree)
   }
 
-  override val cpy = new TypedTreeCopier
+  override val cpy: TypedTreeCopier = // Type ascription needed to pick up any new members in TreeCopier (currently there are none)
+    new TypedTreeCopier
 
   class TypedTreeCopier extends TreeCopier {
     def postProcess(tree: Tree, copied: untpd.Tree): copied.ThisTree[Type] =

compiler/src/dotty/tools/dotc/ast/untpd.scala

@@ -53,6 +53,12 @@ object untpd extends Trees.Instance[Untyped] with UntypedTreeInfo {
     override def isTerm = body.isTerm
     override def isType = body.isType
   }
+
+  /** An implicit function type */
+  class ImplicitFunction(args: List[Tree], body: Tree) extends Function(args, body) {
+    override def toString = s"ImplicitFunction($args, $body)"
+  }
+
   /** A function created from a wildcard expression
    *  @param  placeHolderParams  a list of definitions of synthetic parameters
    *  @param  body               the function body where wildcards are replaced by
@@ -111,7 +117,7 @@ object untpd extends Trees.Instance[Untyped] with UntypedTreeInfo {
 
     case class Var() extends Mod(Flags.Mutable)
 
-    case class Implicit(flag: FlagSet = Flags.ImplicitCommon) extends Mod(flag)
+    case class Implicit() extends Mod(Flags.ImplicitCommon)
 
     case class Final() extends Mod(Flags.Final)
 
@@ -270,8 +276,6 @@ object untpd extends Trees.Instance[Untyped] with UntypedTreeInfo {
 
   // ------ Additional creation methods for untyped only -----------------
 
-  // def TypeTree(tpe: Type): TypeTree = TypeTree().withType(tpe) todo: move to untpd/tpd
-
   /**     new pre.C[Ts](args1)...(args_n)
    *  ==>
    *      (new pre.C).<init>[Ts](args1)...(args_n)

compiler/src/dotty/tools/dotc/config/JavaPlatform.scala

@@ -18,6 +18,7 @@ class JavaPlatform extends Platform {
       currentClassPath = Some(new PathResolver().result)
     val cp = currentClassPath.get
     //println(cp)
+    //println("------------------")
     cp
   }
 

compiler/src/dotty/tools/dotc/core/Comments.scala

@@ -119,7 +119,7 @@ object Comments {
     def apply(comment: Comment, code: String, codePos: Position)(implicit ctx: Context) =
       new UseCase(comment, code, codePos) {
         val untpdCode = {
-          val tree = new Parser(new SourceFile("<usecase>", code)).localDef(codePos.start, EmptyFlags)
+          val tree = new Parser(new SourceFile("<usecase>", code)).localDef(codePos.start)
 
           tree match {
             case tree: untpd.DefDef =>

compiler/src/dotty/tools/dotc/core/Definitions.scala

@@ -86,24 +86,51 @@ class Definitions {
     newClassSymbol(ScalaPackageClass, name, EmptyFlags, completer).entered
   }
 
-  /** The trait FunctionN, for some N */
-  private def newFunctionNTrait(n: Int) = {
+  /** The trait FunctionN or ImplicitFunctionN, for some N
+   *  @param  name   The name of the trait to be created
+   *
+   *  FunctionN traits follow this template:
+   *
+   *      trait FunctionN[T0,...T{N-1}, R] extends Object {
+   *        def apply($x0: T0, ..., $x{N_1}: T{N-1}): R
+   *      }
+   *
+   *  That is, they follow the template given for Function2..Function22 in the
+   *  standard library, but without `tupled` and `curried` methods and without
+   *  a `toString`.
+   *
+   *  ImplicitFunctionN traits follow this template:
+   *
+   *      trait ImplicitFunctionN[T0,...,T{N-1}, R] extends Object with FunctionN[T0,...,T{N-1}, R] {
+   *        def apply(implicit $x0: T0, ..., $x{N_1}: T{N-1}): R
+   *      }
+   */
+  private def newFunctionNTrait(name: TypeName) = {
     val completer = new LazyType {
       def complete(denot: SymDenotation)(implicit ctx: Context): Unit = {
         val cls = denot.asClass.classSymbol
         val decls = newScope
+        val arity = name.functionArity
         val argParams =
-          for (i <- List.range(0, n)) yield
-            enterTypeParam(cls, s"T$i".toTypeName, Contravariant, decls)
-        val resParam = enterTypeParam(cls, s"R".toTypeName, Covariant, decls)
+          for (i <- List.range(0, arity)) yield
+            enterTypeParam(cls, name ++ "$T" ++ i.toString, Contravariant, decls)
+        val resParam = enterTypeParam(cls, name ++ "$R", Covariant, decls)
+        val (methodType, parentTraits) =
+          if (name.startsWith(tpnme.ImplicitFunction)) {
+            val superTrait =
+              FunctionType(arity).appliedTo(argParams.map(_.typeRef) ::: resParam.typeRef :: Nil)
+            (ImplicitMethodType, ctx.normalizeToClassRefs(superTrait :: Nil, cls, decls))
+          }
+          else (MethodType, Nil)
         val applyMeth =
           decls.enter(
             newMethod(cls, nme.apply,
-              MethodType(argParams.map(_.typeRef), resParam.typeRef), Deferred))
-        denot.info = ClassInfo(ScalaPackageClass.thisType, cls, ObjectType :: Nil, decls)
+              methodType(argParams.map(_.typeRef), resParam.typeRef), Deferred))
+        denot.info =
+          ClassInfo(ScalaPackageClass.thisType, cls, ObjectType :: parentTraits, decls)
       }
     }
-    newClassSymbol(ScalaPackageClass, s"Function$n".toTypeName, Trait, completer)
+    newClassSymbol(ScalaPackageClass, name, Trait, completer)
   }
 
   private def newMethod(cls: ClassSymbol, name: TermName, info: Type, flags: FlagSet = EmptyFlags): TermSymbol =
@@ -590,15 +617,16 @@ class Definitions {
     sym.owner.linkedClass.typeRef
 
   object FunctionOf {
-    def apply(args: List[Type], resultType: Type)(implicit ctx: Context) =
-      FunctionType(args.length).appliedTo(args ::: resultType :: Nil)
+    def apply(args: List[Type], resultType: Type, isImplicit: Boolean = false)(implicit ctx: Context) =
+      FunctionType(args.length, isImplicit).appliedTo(args ::: resultType :: Nil)
     def unapply(ft: Type)(implicit ctx: Context) = {
       val tsym = ft.typeSymbol
-      if (isFunctionClass(tsym)) {
-        lazy val targs = ft.argInfos
+      val isImplicitFun = isImplicitFunctionClass(tsym)
+      if (isImplicitFun || isFunctionClass(tsym)) {
+        val targs = ft.argInfos
         val numArgs = targs.length - 1
-        if (numArgs >= 0 && FunctionType(numArgs).symbol == tsym)
-          Some(targs.init, targs.last)
+        if (numArgs >= 0 && FunctionType(numArgs, isImplicitFun).symbol == tsym)
+          Some(targs.init, targs.last, isImplicitFun)
         else None
       }
       else None
@@ -659,8 +687,12 @@ class Definitions {
     lazy val Function0_applyR = ImplementedFunctionType(0).symbol.requiredMethodRef(nme.apply)
     def Function0_apply(implicit ctx: Context) = Function0_applyR.symbol
 
-  def FunctionType(n: Int)(implicit ctx: Context): TypeRef =
-    if (n < MaxImplementedFunctionArity) ImplementedFunctionType(n)
+  def ImplicitFunctionClass(n: Int)(implicit ctx: Context) =
+    ctx.requiredClass("scala.ImplicitFunction" + n.toString)
+
+  def FunctionType(n: Int, isImplicit: Boolean = false)(implicit ctx: Context): TypeRef =
+    if (isImplicit && !ctx.erasedTypes) ImplicitFunctionClass(n).typeRef
+    else if (n < MaxImplementedFunctionArity) ImplementedFunctionType(n)
     else FunctionClass(n).typeRef
 
   private lazy val TupleTypes: Set[TypeRef] = TupleType.toSet
@@ -686,6 +718,7 @@ class Definitions {
     tp.derivesFrom(NothingClass) || tp.derivesFrom(NullClass)
 
   def isFunctionClass(cls: Symbol) = isVarArityClass(cls, tpnme.Function)
+  def isImplicitFunctionClass(cls: Symbol) = isVarArityClass(cls, tpnme.ImplicitFunction)
   def isUnimplementedFunctionClass(cls: Symbol) =
     isFunctionClass(cls) && cls.name.functionArity > MaxImplementedFunctionArity
   def isAbstractFunctionClass(cls: Symbol) = isVarArityClass(cls, tpnme.AbstractFunction)
@@ -745,14 +778,21 @@ class Definitions {
       }
     else -1
 
-  def isFunctionType(tp: Type)(implicit ctx: Context) =
-    isFunctionClass(tp.dealias.typeSymbol) && {
-      val arity = functionArity(tp)
-      arity >= 0 && tp.isRef(FunctionType(functionArity(tp)).typeSymbol)
-    }
+  /** Is `tp` (an alias) of either a scala.FunctionN or a scala.ImplicitFunctionN ? */
+  def isFunctionType(tp: Type)(implicit ctx: Context) = {
+    val arity = functionArity(tp)
+    val sym = tp.dealias.typeSymbol
+    arity >= 0 && (
+      isFunctionClass(sym) && tp.isRef(FunctionType(arity, isImplicit = false).typeSymbol) ||
+      isImplicitFunctionClass(sym) && tp.isRef(FunctionType(arity, isImplicit = true).typeSymbol)
+    )
+  }
 
   def functionArity(tp: Type)(implicit ctx: Context) = tp.dealias.argInfos.length - 1
 
+  def isImplicitFunctionType(tp: Type)(implicit ctx: Context) =
+    isFunctionType(tp) && tp.dealias.typeSymbol.name.startsWith(tpnme.ImplicitFunction)
+
   // ----- primitive value class machinery ------------------------------------------
 
   /** This class would also be obviated by the implicit function type design */
@@ -825,6 +865,9 @@ class Definitions {
 
   // ----- Initialization ---------------------------------------------------
 
+  private def maxImplemented(name: Name) =
+    if (name `startsWith` tpnme.Function) MaxImplementedFunctionArity else 0
+
   /** Give the scala package a scope where a FunctionN trait is automatically
    *  added when someone looks for it.
    */
@@ -834,8 +877,8 @@ class Definitions {
     val newDecls = new MutableScope(oldDecls) {
       override def lookupEntry(name: Name)(implicit ctx: Context): ScopeEntry = {
         val res = super.lookupEntry(name)
-        if (res == null && name.functionArity > MaxImplementedFunctionArity)
-          newScopeEntry(newFunctionNTrait(name.functionArity))
+        if (res == null && name.isTypeName && name.functionArity > maxImplemented(name))
+          newScopeEntry(newFunctionNTrait(name.asTypeName))
         else res
       }
     }