X-Git-Url: http://git.megacz.com/?a=blobdiff_plain;f=compiler%2Futils%2FIOEnv.hs;h=b81b2e8fde943c30e710b257a686d76e5c11f070;hb=d436c70d43fb905c63220040168295e473f4b90a;hp=61345ca246aa41243a7849838f5864b4830d48be;hpb=f4ce543cff19b797d54d435dc7c804acdefca9c8;p=ghc-hetmet.git

diff --git a/compiler/utils/IOEnv.hs b/compiler/utils/IOEnv.hs
index 61345ca..b81b2e8 100644
--- a/compiler/utils/IOEnv.hs
+++ b/compiler/utils/IOEnv.hs
@@ -3,6 +3,7 @@
 --
 -- The IO Monad with an environment
 --
+{-# LANGUAGE UndecidableInstances #-}
 
 module IOEnv (
         IOEnv, -- Instance of Monad
@@ -31,6 +32,7 @@ import Data.IORef       ( IORef, newIORef, readIORef, writeIORef, modifyIORef )
 import Data.Typeable
 import System.IO.Unsafe ( unsafeInterleaveIO )
 import System.IO        ( fixIO )
+import Control.Monad
 import MonadUtils
 
 ----------------------------------------------------------------------
@@ -64,7 +66,7 @@ thenM (IOEnv m) f = IOEnv (\ env -> do { r <- m env ;
                                          unIOEnv (f r) env })
 
 thenM_ :: IOEnv env a -> IOEnv env b -> IOEnv env b
-thenM_ (IOEnv m) f = IOEnv (\ env -> do { m env ; unIOEnv f env })
+thenM_ (IOEnv m) f = IOEnv (\ env -> do { _ <- m env ; unIOEnv f env })
 
 failM :: IOEnv env a
 failM = IOEnv (\ _ -> throwIO IOEnvFailure)
@@ -132,6 +134,16 @@ unsafeInterleaveM (IOEnv m) = IOEnv (\ env -> unsafeInterleaveIO (m env))
 
 
 ----------------------------------------------------------------------
+-- MonadPlus
+----------------------------------------------------------------------
+
+-- For use if the user has imported Control.Monad.Error from MTL
+-- Requires UndecidableInstances
+instance MonadPlus IO => MonadPlus (IOEnv env) where
+    mzero = IOEnv (const mzero)
+    m `mplus` n = IOEnv (\env -> unIOEnv m env `mplus` unIOEnv n env)
+
+----------------------------------------------------------------------
 -- Accessing input/output
 ----------------------------------------------------------------------