Add cons

Author: hdgarrood

docs/Data.Array.md

@@ -20,6 +20,30 @@ for many use cases due to their poor asymptotics.
 This operator provides a safe way to read a value at a particular index
 from an array.
 
+#### `cons`
+
+``` purescript
+cons :: forall a. a -> [a] -> [a]
+```
+
+Attaches an element to the front of an array, creating a new array.
+
+```purescript
+cons 1 [2, 3, 4] = [1, 2, 3, 4]
+```
+
+Note, the running time of this function is `O(n)`.
+
+#### `(:)`
+
+``` purescript
+(:) :: forall a. a -> [a] -> [a]
+```
+
+An infix alias for `cons`.
+
+Note, the running time of this function is `O(n)`.
+
 #### `snoc`
 
 ``` purescript

src/Data/Array.purs

@@ -8,6 +8,8 @@
 module Data.Array
   ( (!!)
   , (..)
+  , cons
+  , (:)
   , snoc
   , singleton
   , head
@@ -72,6 +74,30 @@ infixl 8 !!
 (!!) xs n | n < zero || n >= length xs = Nothing
           | otherwise = Just (xs `unsafeIndex` toNumber n)
 
+-- | Attaches an element to the front of an array, creating a new array.
+-- |
+-- | ```purescript
+-- | cons 1 [2, 3, 4] = [1, 2, 3, 4]
+-- | ```
+-- |
+-- | Note, the running time of this function is `O(n)`.
+foreign import cons
+  """
+  function cons(e) {
+    return function(l) {
+      return [e].concat(l);
+    };
+  }
+  """ :: forall a. a -> [a] -> [a]
+
+infixr 6 :
+
+-- | An infix alias for `cons`.
+-- |
+-- | Note, the running time of this function is `O(n)`.
+(:) :: forall a. a -> [a] -> [a]
+(:) = cons
+
 -- | Append an element to the end of an array, creating a new array.
 foreign import snoc
   """