From: Ross Paterson <ross@soi.city.ac.uk>
Date: Mon, 10 Apr 2006 11:14:43 +0000 (+0000)
Subject: add Functor and Monad instances for Prelude types
X-Git-Tag: 2007-09-13~394
X-Git-Url: http://git.megacz.com/?a=commitdiff_plain;h=4d6fe46a37ba0e82c4182cd26a9e89a258b0c6df;p=ghc-base.git

add Functor and Monad instances for Prelude types
---

diff --git a/Control/Monad/Fix.hs b/Control/Monad/Fix.hs
index a24d9af..e04a7f6 100644
--- a/Control/Monad/Fix.hs
+++ b/Control/Monad/Fix.hs
@@ -24,6 +24,7 @@ module Control.Monad.Fix (
 
 import Prelude
 import System.IO
+import Control.Monad.Instances ()
 
 -- | @'fix' f@ is the least fixed point of the function @f@,
 -- i.e. the least defined @x@ such that @f x = x@.
@@ -71,3 +72,6 @@ instance MonadFix [] where
 -- IO:
 instance MonadFix IO where
     mfix = fixIO 
+
+instance MonadFix ((->) r) where
+    mfix f = \ r -> let a = f a r in a
diff --git a/Control/Monad/Instances.hs b/Control/Monad/Instances.hs
new file mode 100644
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)
diff --git a/base.cabal b/base.cabal
index c45ccd4..4d5a6e8 100644
--- a/base.cabal
+++ b/base.cabal
@@ -20,6 +20,7 @@ exposed-modules:
 	Control.Exception,
 	Control.Monad,
 	Control.Monad.Fix,
+	Control.Monad.Instances,
 	Control.Monad.ST,
 	Control.Monad.ST.Lazy,
 	Control.Monad.ST.Strict,
diff --git a/package.conf.in b/package.conf.in
index 2c8067e..947d191 100644
--- a/package.conf.in
+++ b/package.conf.in
@@ -18,6 +18,7 @@ exposed-modules:
 	Control.Exception,
 	Control.Monad,
 	Control.Monad.Fix,
+	Control.Monad.Instances,
 	Control.Monad.ST,
 	Control.Monad.ST.Lazy,
 	Control.Monad.ST.Strict,