Merge pull request #25 from purescript/maybe

Add instances for Maybe

Author: garyb

src/Data/Unfoldable.purs

@@ -41,6 +41,9 @@ class Unfoldable1 t <= Unfoldable t where
 instance unfoldableArray :: Unfoldable Array where
   unfoldr = unfoldrArrayImpl isNothing (unsafePartial fromJust) fst snd
 
+instance unfoldableMaybe :: Unfoldable Maybe where
+  unfoldr f b = fst <$> f b
+
 foreign import unfoldrArrayImpl
   :: forall a b
    . (forall x. Maybe x -> Boolean)

src/Data/Unfoldable1.purs

@@ -41,6 +41,9 @@ class Unfoldable1 t where
 instance unfoldable1Array :: Unfoldable1 Array where
   unfoldr1 = unfoldr1ArrayImpl isNothing (unsafePartial fromJust) fst snd
 
+instance unfoldable1Maybe :: Unfoldable1 Maybe where
+  unfoldr1 f b = Just (fst (f b))
+
 foreign import unfoldr1ArrayImpl
   :: forall a b
    . (forall x. Maybe x -> Boolean)