-- Hoogle documentation, generated by Haddock
-- See Hoogle, http://www.haskell.org/hoogle/


-- | A small library providing a contravariant functor class
--   
--   This library provides a <a>Cofunctor</a> class useful for types that
--   are sinks or make use of IO effects. See documentation for details.
--   Some supporting constructions are also provided.
@package cofunctor
@version 0.1.0

module Data.Cofunctor

-- | The Confunctor class is useful for "sink-like" types, especially when
--   combined with GADTs. For instance:
--   
--   <pre>
--   
--   data StringStack a where
--       StringStack :: (a -&gt; String) -&gt; [String] -&gt; StringStack a
--   
--   emptyStack :: StringStack String
--   emptyStack = StringStack id []
--   
--   push :: a -&gt; StringStack a -&gt; StringStack a
--   push a (StringStack f ss) = StringStack f (f s : ss)
--   
--   instance Confunctor StringStack where
--       cofmap f (StringStack g ss) = StringStack (g . f) ss
--   </pre>
--   
--   See the <a>split-chan</a> package for another example.
--   
--   A class for contravariant functors
class Cofunctor f
cofmap :: Cofunctor f => (b -> a) -> f a -> f b