[commit: haskeline] master: #117: Implement mapInputT. (8da2956)

[Ian Lynagh]

Repository : ssh://darcs.haskell.org//srv/darcs/packages/haskeline

On branch  : master

http://hackage.haskell.org/trac/ghc/changeset/8da29568eca603b174b9bc53a65da53387b3392a

>---------------------------------------------------------------

commit 8da29568eca603b174b9bc53a65da53387b3392a
Author: Judah Jacobson <judah.jacobson at gmail.com>
Date:   Fri Mar 23 16:54:47 2012 +0000

    #117: Implement mapInputT.

>---------------------------------------------------------------

 System/Console/Haskeline.hs        |    1 +
 System/Console/Haskeline/InputT.hs |    5 +++++
 System/Console/Haskeline/Monads.hs |    5 +++++
 3 files changed, 11 insertions(+), 0 deletions(-)

diff --git a/System/Console/Haskeline.hs b/System/Console/Haskeline.hs
index 715b382..bc5db8f 100644
--- a/System/Console/Haskeline.hs
+++ b/System/Console/Haskeline.hs
@@ -32,6 +32,7 @@ module System.Console.Haskeline(
                     InputT,
                     runInputT,
                     haveTerminalUI,
+                    mapInputT,
                     -- ** Behaviors
                     Behavior,
                     runInputTBehavior,
diff --git a/System/Console/Haskeline/InputT.hs b/System/Console/Haskeline/InputT.hs
index 9129a91..fba5705 100644
--- a/System/Console/Haskeline/InputT.hs
+++ b/System/Console/Haskeline/InputT.hs
@@ -150,6 +150,11 @@ execInputT prefs settings run (InputT f)
             $ runHistoryFromFile (historyFile settings) (maxHistorySize prefs)
             $ runReaderT f run
 
+-- | Map a user interaction by modifying the base monad computation.
+mapInputT :: (forall b . m b -> m b) -> InputT m a -> InputT m a
+mapInputT f = InputT . mapReaderT (mapStateT (mapStateT 
+                                  (mapReaderT (mapReaderT f))))
+                    . unInputT
 
 -- | Read input from 'stdin'.  
 -- Use terminal-style interaction if 'stdin' is connected to
diff --git a/System/Console/Haskeline/Monads.hs b/System/Console/Haskeline/Monads.hs
index 75de7c2..9dd4aa1 100644
--- a/System/Console/Haskeline/Monads.hs
+++ b/System/Console/Haskeline/Monads.hs
@@ -3,10 +3,12 @@ module System.Console.Haskeline.Monads(
                 module System.Console.Haskeline.MonadException,
                 ReaderT(..),
                 runReaderT',
+                mapReaderT,
                 asks,
                 StateT,
                 runStateT,
                 evalStateT',
+                mapStateT,
                 gets,
                 modify,
                 update,
@@ -75,6 +77,9 @@ instance MonadTrans (StateT s) where
 instance MonadIO m => MonadIO (StateT s m) where
     liftIO = lift . liftIO
 
+mapStateT :: (forall b . m b -> n b) -> StateT s m a -> StateT s n a
+mapStateT f (StateT m) = StateT (\s -> f (m s))
+
 runStateT :: Monad m => StateT s m a -> s -> m (a, s)
 runStateT f s = do
     useXS <- getStateTFunc f s