Merge pull request #5 from sharkdp/add-head-tail

Add head, tail

Author: paf31

docs/Data/NonEmpty.md

@@ -21,12 +21,12 @@ nonEmptyList = 0 :| empty
 
 ##### Instances
 ``` purescript
-instance showNonEmpty :: (Show a, Show (f a)) => Show (NonEmpty f a)
-instance eqNonEmpty :: (Eq a, Eq (f a)) => Eq (NonEmpty f a)
-instance ordNonEmpty :: (Ord a, Ord (f a)) => Ord (NonEmpty f a)
-instance functorNonEmpty :: (Functor f) => Functor (NonEmpty f)
-instance foldableNonEmpty :: (Foldable f) => Foldable (NonEmpty f)
-instance traversableNonEmpty :: (Traversable f) => Traversable (NonEmpty f)
+(Show a, Show (f a)) => Show (NonEmpty f a)
+(Eq a, Eq (f a)) => Eq (NonEmpty f a)
+(Ord a, Ord (f a)) => Ord (NonEmpty f a)
+(Functor f) => Functor (NonEmpty f)
+(Foldable f) => Foldable (NonEmpty f)
+(Traversable f) => Traversable (NonEmpty f)
 ```
 
 #### `singleton`
@@ -50,7 +50,7 @@ An infix synonym for `NonEmpty`.
 #### `foldl1`
 
 ``` purescript
-foldl1 :: forall f a s. (Foldable f) => (a -> a -> a) -> NonEmpty f a -> a
+foldl1 :: forall f a. (Foldable f) => (a -> a -> a) -> NonEmpty f a -> a
 ```
 
 Fold a non-empty structure, collecting results using a binary operation.
@@ -83,4 +83,20 @@ fromNonEmpty :: forall f a r. (a -> f a -> r) -> NonEmpty f a -> r
 oneOf :: forall f a. (Alternative f) => NonEmpty f a -> f a
 ```
 
+#### `head`
+
+``` purescript
+head :: forall f a. NonEmpty f a -> a
+```
+
+Get the 'first' element of a non-empty container.
+
+#### `tail`
+
+``` purescript
+tail :: forall f a. NonEmpty f a -> f a
+```
+
+Get everything but the 'first' element of a non-empty container.
+
 

src/Data/NonEmpty.purs

@@ -10,6 +10,8 @@ module Data.NonEmpty
   , fold1
   , fromNonEmpty
   , oneOf
+  , head
+  , tail
   ) where
 
 import Prelude
@@ -59,6 +61,14 @@ fromNonEmpty f (NonEmpty a fa) = a `f` fa
 oneOf :: forall f a. (Alternative f) => NonEmpty f a -> f a
 oneOf (NonEmpty a fa) = pure a <|> fa
 
+-- | Get the 'first' element of a non-empty container.
+head :: forall f a. NonEmpty f a -> a
+head (NonEmpty x _) = x
+
+-- | Get everything but the 'first' element of a non-empty container.
+tail :: forall f a. NonEmpty f a -> f a
+tail (NonEmpty _ xs) = xs
+
 instance showNonEmpty :: (Show a, Show (f a)) => Show (NonEmpty f a) where
   show (NonEmpty a fa) = "(NonEmpty " ++ show a ++ " " ++ show fa ++ ")"