Merge pull request #10 from joneshf/master

Added Comonad/Extend.

Author: garyb

README.md

@@ -62,6 +62,38 @@ If you are have a conflict between `<|>` in `Prelude` and `Control.Alt` please u
     join :: forall a m. (Bind m) => m (m a) -> m a
 
 
+## Module Control.Comonad
+
+### Type Classes
+
+    class (Extend w) <= Comonad w where
+      extract :: forall a. w a -> a
+
+
+## Module Control.Extend
+
+### Type Classes
+
+    class (Functor w) <= Extend w where
+      (<<=) :: forall b a. (w a -> b) -> w a -> w b
+
+
+### Type Class Instances
+
+    instance extendArr :: (Semigroup w) => Extend (Prim.Function w)
+
+
+### Values
+
+    (=<=) :: forall b a w c. (Extend w) => (w b -> c) -> (w a -> b) -> w a -> c
+
+    (=>=) :: forall b a w c. (Extend w) => (w a -> b) -> (w b -> c) -> w a -> c
+
+    (=>>) :: forall b a w. (Extend w) => w a -> (w a -> b) -> w b
+
+    duplicate :: forall a w. (Extend w) => w a -> w (w a)
+
+
 ## Module Control.Lazy
 
 ### Type Classes

src/Control/Comonad.purs

@@ -0,0 +1,6 @@
+module Control.Comonad where
+
+import Control.Extend
+
+class (Extend w) <= Comonad w where
+  extract :: forall a. w a -> a

src/Control/Extend.purs

@@ -0,0 +1,24 @@
+module Control.Extend where
+
+infixl 1 =>>
+infixr 1 <<=
+infixr 1 =>=
+infixr 1 =<=
+
+class (Functor w) <= Extend w where
+  (<<=) :: forall b a. (w a -> b) -> w a -> w b
+
+instance extendArr :: (Semigroup w) => Extend ((->) w) where
+  (<<=) f g w = f \w' -> g (w <> w')
+
+(=>>) :: forall b a w. (Extend w) => w a -> (w a -> b) -> w b
+(=>>) w f = f <<= w
+
+(=>=) :: forall b a w c. (Extend w) => (w a -> b) -> (w b -> c) -> w a -> c
+(=>=) f g w = g (f <<= w)
+
+(=<=) :: forall b a w c. (Extend w) => (w b -> c) -> (w a -> b) -> w a -> c
+(=<=) f g w = f (g <<= w)
+
+duplicate :: forall a w. (Extend w) => w a -> w (w a)
+duplicate w = id <<= w