From a4bf08c42601244cf8805128b8b22c90d5324520 Mon Sep 17 00:00:00 2001
From: Phil Freeman <paf31@cantab.net>
Date: Sun, 8 Mar 2015 14:45:25 -0700
Subject: [PATCH] Add modifyAt

---
 README.md           | 495 +++++++++++++++++++++++++++++++++++++-------
 src/Data/Array.purs |   6 +
 2 files changed, 426 insertions(+), 75 deletions(-)

diff --git a/README.md b/README.md
index f08f2633..22c03f9a 100644
--- a/README.md
+++ b/README.md
@@ -2,160 +2,505 @@
 
 ## Module Data.Array
 
-### Type Class Instances
+#### `(!!)`
 
-    instance altArray :: Alt Prim.Array
+``` purescript
+(!!) :: forall a. [a] -> Number -> Maybe a
+```
 
-    instance alternativeArray :: Alternative Prim.Array
 
-    instance applicativeArray :: Applicative Prim.Array
+#### `snoc`
 
-    instance applyArray :: Apply Prim.Array
+``` purescript
+snoc :: forall a. [a] -> a -> [a]
+```
 
-    instance bindArray :: Bind Prim.Array
 
-    instance functorArray :: Functor Prim.Array
+#### `singleton`
 
-    instance monadArray :: Monad Prim.Array
+``` purescript
+singleton :: forall a. a -> [a]
+```
 
-    instance monadPlusArray :: MonadPlus Prim.Array
 
-    instance plusArray :: Plus Prim.Array
+#### `head`
 
-    instance semigroupArray :: Semigroup [a]
+``` purescript
+head :: forall a. [a] -> Maybe a
+```
 
 
-### Values
+#### `last`
 
-    (!!) :: forall a. [a] -> Number -> Maybe a
+``` purescript
+last :: forall a. [a] -> Maybe a
+```
 
-    (..) :: Number -> Number -> [Number]
 
-    (\\) :: forall a. (Eq a) => [a] -> [a] -> [a]
+#### `tail`
 
-    append :: forall a. [a] -> [a] -> [a]
+``` purescript
+tail :: forall a. [a] -> Maybe [a]
+```
 
-    catMaybes :: forall a. [Maybe a] -> [a]
 
-    concat :: forall a. [[a]] -> [a]
+#### `init`
 
-    concatMap :: forall a b. (a -> [b]) -> [a] -> [b]
+``` purescript
+init :: forall a. [a] -> Maybe [a]
+```
 
-    delete :: forall a. (Eq a) => a -> [a] -> [a]
 
-    deleteAt :: forall a. Number -> Number -> [a] -> [a]
+#### `null`
 
-    deleteBy :: forall a. (a -> a -> Boolean) -> a -> [a] -> [a]
+``` purescript
+null :: forall a. [a] -> Boolean
+```
 
-    drop :: forall a. Number -> [a] -> [a]
 
-    dropWhile :: forall a. (a -> Boolean) -> [a] -> [a]
+#### `length`
 
-    elemIndex :: forall a. (Eq a) => a -> [a] -> Number
+``` purescript
+length :: forall a. [a] -> Number
+```
 
-    elemLastIndex :: forall a. (Eq a) => a -> [a] -> Number
 
-    filter :: forall a. (a -> Boolean) -> [a] -> [a]
+#### `findIndex`
 
-    findIndex :: forall a. (a -> Boolean) -> [a] -> Number
+``` purescript
+findIndex :: forall a. (a -> Boolean) -> [a] -> Number
+```
 
-    findLastIndex :: forall a. (a -> Boolean) -> [a] -> Number
 
-    group :: forall a. (Eq a) => [a] -> [[a]]
+#### `findLastIndex`
 
-    group' :: forall a. (Ord a) => [a] -> [[a]]
+``` purescript
+findLastIndex :: forall a. (a -> Boolean) -> [a] -> Number
+```
 
-    groupBy :: forall a. (a -> a -> Boolean) -> [a] -> [[a]]
 
-    head :: forall a. [a] -> Maybe a
+#### `elemIndex`
 
-    init :: forall a. [a] -> Maybe [a]
+``` purescript
+elemIndex :: forall a. (Eq a) => a -> [a] -> Number
+```
 
-    insertAt :: forall a. Number -> a -> [a] -> [a]
 
-    intersect :: forall a. (Eq a) => [a] -> [a] -> [a]
+#### `elemLastIndex`
 
-    intersectBy :: forall a. (a -> a -> Boolean) -> [a] -> [a] -> [a]
+``` purescript
+elemLastIndex :: forall a. (Eq a) => a -> [a] -> Number
+```
 
-    last :: forall a. [a] -> Maybe a
 
-    length :: forall a. [a] -> Number
+#### `append`
 
-    map :: forall a b. (a -> b) -> [a] -> [b]
+``` purescript
+append :: forall a. [a] -> [a] -> [a]
+```
 
-    mapMaybe :: forall a b. (a -> Maybe b) -> [a] -> [b]
 
-    nub :: forall a. (Eq a) => [a] -> [a]
+#### `concat`
 
-    nubBy :: forall a. (a -> a -> Boolean) -> [a] -> [a]
+``` purescript
+concat :: forall a. [[a]] -> [a]
+```
 
-    null :: forall a. [a] -> Boolean
 
-    range :: Number -> Number -> [Number]
+#### `reverse`
 
-    reverse :: forall a. [a] -> [a]
+``` purescript
+reverse :: forall a. [a] -> [a]
+```
 
-    singleton :: forall a. a -> [a]
 
-    snoc :: forall a. [a] -> a -> [a]
+#### `drop`
 
-    sort :: forall a. (Ord a) => [a] -> [a]
+``` purescript
+drop :: forall a. Number -> [a] -> [a]
+```
 
-    sortBy :: forall a. (a -> a -> Ordering) -> [a] -> [a]
 
-    span :: forall a. (a -> Boolean) -> [a] -> { rest :: [a], init :: [a] }
+#### `take`
 
-    tail :: forall a. [a] -> Maybe [a]
+``` purescript
+take :: forall a. Number -> [a] -> [a]
+```
 
-    take :: forall a. Number -> [a] -> [a]
 
-    takeWhile :: forall a. (a -> Boolean) -> [a] -> [a]
+#### `insertAt`
 
-    updateAt :: forall a. Number -> a -> [a] -> [a]
+``` purescript
+insertAt :: forall a. Number -> a -> [a] -> [a]
+```
+
+
+#### `deleteAt`
+
+``` purescript
+deleteAt :: forall a. Number -> Number -> [a] -> [a]
+```
+
+
+#### `updateAt`
+
+``` purescript
+updateAt :: forall a. Number -> a -> [a] -> [a]
+```
+
+
+#### `modifyAt`
+
+``` purescript
+modifyAt :: forall a. Number -> (a -> a) -> [a] -> [a]
+```
+
+
+#### `deleteBy`
+
+``` purescript
+deleteBy :: forall a. (a -> a -> Boolean) -> a -> [a] -> [a]
+```
+
+
+#### `delete`
+
+``` purescript
+delete :: forall a. (Eq a) => a -> [a] -> [a]
+```
+
+
+#### `(\\)`
+
+``` purescript
+(\\) :: forall a. (Eq a) => [a] -> [a] -> [a]
+```
+
+
+#### `intersectBy`
+
+``` purescript
+intersectBy :: forall a. (a -> a -> Boolean) -> [a] -> [a] -> [a]
+```
+
+
+#### `intersect`
+
+``` purescript
+intersect :: forall a. (Eq a) => [a] -> [a] -> [a]
+```
+
+
+#### `concatMap`
+
+``` purescript
+concatMap :: forall a b. (a -> [b]) -> [a] -> [b]
+```
+
+
+#### `map`
+
+``` purescript
+map :: forall a b. (a -> b) -> [a] -> [b]
+```
+
+
+#### `mapMaybe`
+
+``` purescript
+mapMaybe :: forall a b. (a -> Maybe b) -> [a] -> [b]
+```
+
+
+#### `catMaybes`
+
+``` purescript
+catMaybes :: forall a. [Maybe a] -> [a]
+```
+
+
+#### `filter`
+
+``` purescript
+filter :: forall a. (a -> Boolean) -> [a] -> [a]
+```
+
+
+#### `range`
+
+``` purescript
+range :: Number -> Number -> [Number]
+```
+
+
+#### `(..)`
+
+``` purescript
+(..) :: Number -> Number -> [Number]
+```
+
+
+#### `zipWith`
+
+``` purescript
+zipWith :: forall a b c. (a -> b -> c) -> [a] -> [b] -> [c]
+```
+
+
+#### `nub`
+
+``` purescript
+nub :: forall a. (Eq a) => [a] -> [a]
+```
+
+
+#### `nubBy`
+
+``` purescript
+nubBy :: forall a. (a -> a -> Boolean) -> [a] -> [a]
+```
+
+
+#### `sort`
+
+``` purescript
+sort :: forall a. (Ord a) => [a] -> [a]
+```
+
+
+#### `sortBy`
+
+``` purescript
+sortBy :: forall a. (a -> a -> Ordering) -> [a] -> [a]
+```
+
+
+#### `group`
+
+``` purescript
+group :: forall a. (Eq a) => [a] -> [[a]]
+```
+
+
+#### `group'`
+
+``` purescript
+group' :: forall a. (Ord a) => [a] -> [[a]]
+```
+
+Performs a sorting first.
+
+#### `groupBy`
+
+``` purescript
+groupBy :: forall a. (a -> a -> Boolean) -> [a] -> [[a]]
+```
+
+
+#### `span`
+
+``` purescript
+span :: forall a. (a -> Boolean) -> [a] -> { rest :: [a], init :: [a] }
+```
+
+
+#### `takeWhile`
+
+``` purescript
+takeWhile :: forall a. (a -> Boolean) -> [a] -> [a]
+```
+
+
+#### `dropWhile`
+
+``` purescript
+dropWhile :: forall a. (a -> Boolean) -> [a] -> [a]
+```
+
+
+#### `functorArray`
+
+``` purescript
+instance functorArray :: Functor Prim.Array
+```
+
+
+#### `applyArray`
+
+``` purescript
+instance applyArray :: Apply Prim.Array
+```
+
+
+#### `applicativeArray`
+
+``` purescript
+instance applicativeArray :: Applicative Prim.Array
+```
+
+
+#### `bindArray`
+
+``` purescript
+instance bindArray :: Bind Prim.Array
+```
+
+
+#### `monadArray`
+
+``` purescript
+instance monadArray :: Monad Prim.Array
+```
+
+
+#### `semigroupArray`
+
+``` purescript
+instance semigroupArray :: Semigroup [a]
+```
+
+
+#### `altArray`
+
+``` purescript
+instance altArray :: Alt Prim.Array
+```
+
+
+#### `plusArray`
+
+``` purescript
+instance plusArray :: Plus Prim.Array
+```
+
+
+#### `alternativeArray`
+
+``` purescript
+instance alternativeArray :: Alternative Prim.Array
+```
+
+
+#### `monadPlusArray`
+
+``` purescript
+instance monadPlusArray :: MonadPlus Prim.Array
+```
 
-    zipWith :: forall a b c. (a -> b -> c) -> [a] -> [b] -> [c]
 
 
 ## Module Data.Array.ST
 
-### Types
+#### `STArray`
+
+``` purescript
+data STArray :: * -> * -> *
+```
+
+
+#### `Assoc`
+
+``` purescript
+type Assoc a = { index :: Number, value :: a }
+```
+
+
+#### `runSTArray`
+
+``` purescript
+runSTArray :: forall a r. (forall h. Eff (st :: ST h | r) (STArray h a)) -> Eff r [a]
+```
+
+
+#### `emptySTArray`
+
+``` purescript
+emptySTArray :: forall a h r. Eff (st :: ST h | r) (STArray h a)
+```
+
 
-    type Assoc a = { index :: Number, value :: a }
+#### `peekSTArray`
 
-    data STArray :: * -> * -> *
+``` purescript
+peekSTArray :: forall a h r. STArray h a -> Number -> Eff (st :: ST h | r) (Maybe a)
+```
 
 
-### Values
+#### `pokeSTArray`
 
-    emptySTArray :: forall a h r. Eff (st :: ST h | r) (STArray h a)
+``` purescript
+pokeSTArray :: forall a h r. STArray h a -> Number -> a -> Eff (st :: ST h | r) Boolean
+```
 
-    freeze :: forall a h r. STArray h a -> Eff (st :: ST h | r) [a]
 
-    peekSTArray :: forall a h r. STArray h a -> Number -> Eff (st :: ST h | r) (Maybe a)
+#### `pushAllSTArray`
 
-    pokeSTArray :: forall a h r. STArray h a -> Number -> a -> Eff (st :: ST h | r) Boolean
+``` purescript
+pushAllSTArray :: forall a h r. STArray h a -> [a] -> Eff (st :: ST h | r) Number
+```
 
-    pushAllSTArray :: forall a h r. STArray h a -> [a] -> Eff (st :: ST h | r) Number
 
-    pushSTArray :: forall a h r. STArray h a -> a -> Eff (st :: ST h | r) Number
+#### `pushSTArray`
 
-    runSTArray :: forall a r. (forall h. Eff (st :: ST h | r) (STArray h a)) -> Eff r [a]
+``` purescript
+pushSTArray :: forall a h r. STArray h a -> a -> Eff (st :: ST h | r) Number
+```
 
-    spliceSTArray :: forall a h r. STArray h a -> Number -> Number -> [a] -> Eff (st :: ST h | r) [a]
 
-    thaw :: forall a h r. [a] -> Eff (st :: ST h | r) (STArray h a)
+#### `spliceSTArray`
+
+``` purescript
+spliceSTArray :: forall a h r. STArray h a -> Number -> Number -> [a] -> Eff (st :: ST h | r) [a]
+```
+
+
+#### `freeze`
+
+``` purescript
+freeze :: forall a h r. STArray h a -> Eff (st :: ST h | r) [a]
+```
+
+
+#### `thaw`
+
+``` purescript
+thaw :: forall a h r. [a] -> Eff (st :: ST h | r) (STArray h a)
+```
+
+
+#### `toAssocArray`
+
+``` purescript
+toAssocArray :: forall a h r. STArray h a -> Eff (st :: ST h | r) [Assoc a]
+```
 
-    toAssocArray :: forall a h r. STArray h a -> Eff (st :: ST h | r) [Assoc a]
 
 
 ## Module Data.Array.Unsafe
 
-### Values
+#### `head`
+
+``` purescript
+head :: forall a. [a] -> a
+```
+
+
+#### `tail`
+
+``` purescript
+tail :: forall a. [a] -> [a]
+```
+
+
+#### `last`
 
-    head :: forall a. [a] -> a
+``` purescript
+last :: forall a. [a] -> a
+```
 
-    init :: forall a. [a] -> [a]
 
-    last :: forall a. [a] -> a
+#### `init`
 
-    tail :: forall a. [a] -> [a]
\ No newline at end of file
+``` purescript
+init :: forall a. [a] -> [a]
+```
\ No newline at end of file
diff --git a/src/Data/Array.purs b/src/Data/Array.purs
index df162114..80d2a165 100644
--- a/src/Data/Array.purs
+++ b/src/Data/Array.purs
@@ -24,6 +24,7 @@ module Data.Array
   , insertAt
   , deleteAt
   , updateAt
+  , modifyAt
   , deleteBy
   , delete
   , (\\)
@@ -205,6 +206,11 @@ foreign import updateAt
   \  };\
   \}":: forall a. Number -> a -> [a] -> [a]
 
+modifyAt :: forall a. Number -> (a -> a) -> [a] -> [a]
+modifyAt i f xs = case xs !! i of
+                    Just x -> updateAt i (f x) xs
+                    Nothing -> xs
+
 deleteBy :: forall a. (a -> a -> Boolean) -> a -> [a] -> [a]
 deleteBy _ _ [] = []
 deleteBy eq x ys = case findIndex (eq x) ys of