Added 'splitAt' function

src/Data/String.js

@@ -139,6 +139,17 @@ exports.split = function (sep) {
   };
 };
 
+exports._splitAt = function (just) {
+  return function (nothing) {
+    return function (i) {
+      return function (s) {
+        return i >= 0 && i < s.length ?
+               just([s.substring(0, i), s.substring(i)]) : nothing;
+      };
+    };
+  };
+};
+
 exports.toCharArray = function (s) {
   return s.split("");
 };

src/Data/String.purs

@@ -25,6 +25,7 @@ module Data.String
   , stripSuffix
   , count
   , split
+  , splitAt
   , toCharArray
   , toLower
   , toUpper
@@ -197,6 +198,16 @@ foreign import count :: (Char -> Boolean) -> String -> Int
 -- | * `split " " "hello world" == ["hello", "world"]`
 foreign import split :: String -> String -> Array String
 
+-- | Returns the substrings of split at the given index, if the index is within bounds.
+splitAt :: Int -> String -> Maybe (Array String)
+splitAt = _splitAt Just Nothing
+
+foreign import _splitAt :: (forall a. a -> Maybe a)
+                        -> (forall a. Maybe a)
+                        -> Int
+                        -> String
+                        -> Maybe (Array String)
+
 -- | Converts the string into an array of characters.
 foreign import toCharArray :: String -> Array Char
 

test/Test/Data/String.purs

@@ -155,6 +155,13 @@ testString = do
   assert $ split "b" "aabcc" == ["aa", "cc"]
   assert $ split "d" "abc" == ["abc"]
 
+  log "splitAt"
+  assert $ splitAt 1 "" == Nothing
+  assert $ splitAt 0 "a" == Just ["", "a"]
+  assert $ splitAt 1 "ab" == Just ["a", "b"]
+  assert $ splitAt 3 "aabcc" == Just ["aab", "cc"]
+  assert $ splitAt (-1) "abc" == Nothing
+
   log "toCharArray"
   assert $ toCharArray "" == []
   assert $ toCharArray "a" == ['a']