X-Git-Url: http://git.megacz.com/?a=blobdiff_plain;f=compiler%2Futils%2FMonadUtils.hs;h=5e01a222b21bdb917853c6c416d5175efbeb98e1;hb=f4b727487a65e6b611bbaafbd2207bd63a8df706;hp=20646572df43aa916498d0c119cdcc7050823231;hpb=0ae16401a0c73548ba4c08f588174f618c363a73;p=ghc-hetmet.git

diff --git a/compiler/utils/MonadUtils.hs b/compiler/utils/MonadUtils.hs
index 2064657..5e01a22 100644
--- a/compiler/utils/MonadUtils.hs
+++ b/compiler/utils/MonadUtils.hs
@@ -8,6 +8,8 @@ module MonadUtils
         
         , MonadFix(..)
         , MonadIO(..)
+	
+  	, ID, runID
         
         , liftIO1, liftIO2, liftIO3, liftIO4
 
@@ -18,9 +20,12 @@ module MonadUtils
         , concatMapM
         , mapMaybeM
         , anyM, allM
-        , foldlM, foldrM
+        , foldlM, foldlM_, foldrM
+        , maybeMapM
         ) where
 
+import Outputable 
+
 ----------------------------------------------------------------------------------------
 -- Detection of available libraries
 ----------------------------------------------------------------------------------------
@@ -42,6 +47,20 @@ import Control.Monad
 import Control.Monad.Fix
 
 ----------------------------------------------------------------------------------------
+-- The ID monad
+----------------------------------------------------------------------------------------
+
+newtype ID a = ID a
+instance Monad ID where
+  return x     = ID x
+  (ID x) >>= f = f x
+  _ >> y       = y
+  fail s       = panic s
+
+runID :: ID a -> a
+runID (ID x) = x
+
+----------------------------------------------------------------------------------------
 -- MTL
 ----------------------------------------------------------------------------------------
 
@@ -145,7 +164,16 @@ allM f (b:bs) = (f b) >>= (\bv -> if bv then allM f bs else return False)
 foldlM :: (Monad m) => (a -> b -> m a) -> a -> [b] -> m a
 foldlM = foldM
 
+-- | Monadic version of foldl that discards its result
+foldlM_ :: (Monad m) => (a -> b -> m a) -> a -> [b] -> m ()
+foldlM_ = foldM_
+
 -- | Monadic version of foldr
 foldrM        :: (Monad m) => (b -> a -> m a) -> a -> [b] -> m a
 foldrM _ z []     = return z
 foldrM k z (x:xs) = do { r <- foldrM k z xs; k x r }
+
+-- | Monadic version of fmap specialised for Maybe
+maybeMapM :: Monad m => (a -> m b) -> (Maybe a -> m (Maybe b))
+maybeMapM _ Nothing  = return Nothing
+maybeMapM m (Just x) = liftM Just $ m x