For a non-recursive let, make sure we extend the value environment

[ghc-hetmet.git] / compiler / utils / MonadUtils.hs

diff --git a/compiler/utils/MonadUtils.hs b/compiler/utils/MonadUtils.hs
index 2064657..dc54620 100644 (file)
--- a/compiler/utils/MonadUtils.hs
+++ b/compiler/utils/MonadUtils.hs
@@ -8,6 +8,8 @@ module MonadUtils
         
         , MonadFix(..)
         , MonadIO(..)
+       
+       , ID, runID
         
         , liftIO1, liftIO2, liftIO3, liftIO4
 
@@ -17,10 +19,14 @@ module MonadUtils
         , mapSndM
         , concatMapM
         , mapMaybeM
+       , fmapMaybeM, fmapEitherM
         , anyM, allM
-        , foldlM, foldrM
+        , foldlM, foldlM_, foldrM
+        , maybeMapM
         ) where
 
+import Outputable 
+
 ----------------------------------------------------------------------------------------
 -- Detection of available libraries
 ----------------------------------------------------------------------------------------
@@ -42,6 +48,20 @@ 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
 ----------------------------------------------------------------------------------------
 
@@ -129,6 +149,16 @@ concatMapM f xs = liftM concat (mapM f xs)
 mapMaybeM :: (Monad m) => (a -> m (Maybe b)) -> [a] -> m [b]
 mapMaybeM f = liftM catMaybes . mapM f
 
+-- | Monadic version of fmap
+fmapMaybeM :: (Monad m) => (a -> m b) -> Maybe a -> m (Maybe b)
+fmapMaybeM _ Nothing  = return Nothing
+fmapMaybeM f (Just x) = f x >>= (return . Just)
+
+-- | Monadic version of fmap
+fmapEitherM :: Monad m => (a -> m b) -> (c -> m d) -> Either a c -> m (Either b d)
+fmapEitherM fl _ (Left  a) = fl a >>= (return . Left)
+fmapEitherM _ fr (Right b) = fr b >>= (return . Right)
+
 -- | Monadic version of 'any', aborts the computation at the first @True@ value
 anyM :: Monad m => (a -> m Bool) -> [a] -> m Bool
 anyM _ []     = return False
@@ -145,7 +175,16 @@ 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