Merge pull request #28 from hdgarrood/better-complexities

make `head` and `last` O(1), not O(n).

Author: paf31

src/Data/Array.purs

@@ -92,16 +92,13 @@ singleton a = [a]
 
 -- | Get the first element in an array, or `Nothing` if the array is empty
 head :: forall a. [a] -> Maybe a
-head (x : _) = Just x
-head _       = Nothing
+head xs = xs !! 0
 
 -- | Get the last element in an array, or `Nothing` if the array is empty
 -- |
 -- | Running time: `O(n)` where `n` is the length of the array
 last :: forall a. [a] -> Maybe a
-last (x : []) = Just x
-last (_ : xs) = last xs
-last _        = Nothing
+last xs = xs !! (length xs - 1)
 
 -- | Get all but the first element of an array, creating a new array, or `Nothing` if the array is empty
 -- |

src/Data/Array/Unsafe.purs

@@ -11,7 +11,7 @@ import qualified Data.Array as A
 
 -- | Get the first element of a non-empty array.
 head :: forall a. [a] -> a
-head (x : _) = x
+head xs = unsafeIndex xs 0
 
 -- | Get all but the first element of a non-empty array.
 tail :: forall a. [a] -> [a]