add Functor and Monad instances for Prelude types

[ghc-base.git] / Control / Monad / Instances.hs

diff --git a/Control/Monad/Instances.hs b/Control/Monad/Instances.hs
new file mode 100644 (file)
index 0000000..1641e03
--- /dev/null
+++ b/Control/Monad/Instances.hs
@@ -0,0 +1,30 @@
+-----------------------------------------------------------------------------
+-- |
+-- Module      :  Control.Monad.Instances
+-- Copyright   :  (c) The University of Glasgow 2001
+-- License     :  BSD-style (see the file libraries/base/LICENSE)
+--
+-- Maintainer  :  libraries@haskell.org
+-- Stability   :  provisional
+-- Portability :  portable
+--
+-- 'Functor' and 'Monad' instances for @(->) r@ and
+-- 'Functor' instances for @(,) a@ and @'Either' a@.
+
+module Control.Monad.Instances () where
+
+import Prelude
+
+instance Functor ((->) r) where
+       fmap = (.)
+
+instance Monad ((->) r) where
+       return = const
+       f >>= k = \ r -> k (f r) r
+
+instance Functor ((,) a) where
+       fmap f (x,y) = (x, f y)
+
+instance Functor (Either a) where
+       fmap _ (Left x) = Left x
+       fmap f (Right y) = Right (f y)