Merge pull request #5 from joneshf/master

Add `Extend` and `Semigroup` instances.

Author: garyb

README.md

@@ -23,6 +23,8 @@
 
     instance eqMaybe :: (Eq a) => Eq (Maybe a)
 
+    instance extendMaybe :: Extend Maybe
+
     instance functorMaybe :: Functor Maybe
 
     instance monadMaybe :: Monad Maybe
@@ -33,6 +35,8 @@
 
     instance plusMaybe :: Plus Maybe
 
+    instance semigroupMaybe :: (Semigroup a) => Semigroup (Maybe a)
+
     instance showMaybe :: (Show a) => Show (Maybe a)
 
 

src/Data/Maybe.purs

@@ -1,9 +1,10 @@
 module Data.Maybe where
 
 import Control.Alt
-import Control.Plus
 import Control.Alternative
+import Control.Extend
 import Control.MonadPlus
+import Control.Plus
 
 data Maybe a = Nothing | Just a
 
@@ -48,6 +49,15 @@ instance monadMaybe :: Monad Maybe
 
 instance monadPlusMaybe :: MonadPlus Maybe
 
+instance extendMaybe :: Extend Maybe where
+  (<<=) _ Nothing  = Nothing
+  (<<=) f x        = Just $ f x
+
+instance semigroupMaybe :: (Semigroup a) => Semigroup (Maybe a) where
+  (<>) Nothing  x        = x
+  (<>) x        Nothing  = x
+  (<>) (Just x) (Just y) = Just (x <> y)
+
 instance showMaybe :: (Show a) => Show (Maybe a) where
   show (Just x) = "Just (" ++ show x ++ ")"
   show Nothing  = "Nothing"