X-Git-Url: http://git.megacz.com/?p=ghc-hetmet.git;a=blobdiff_plain;f=compiler%2Futils%2FMaybes.lhs;h=39e6185a19eedbc355a31573e951e5ac0f05994b;hp=8a6a5f441e2db9fc62b4345047c70d605984c803;hb=8133a9f47b99f4e65ed30551de32ad72c6b61b27;hpb=3659ebdaca5124c4efb9dd9e8894054d34187deb

diff --git a/compiler/utils/Maybes.lhs b/compiler/utils/Maybes.lhs
index 8a6a5f4..39e6185 100644
--- a/compiler/utils/Maybes.lhs
+++ b/compiler/utils/Maybes.lhs
@@ -10,10 +10,11 @@ module Maybes (
         MaybeErr(..), -- Instance of Monad
         failME, isSuccess,
 
+        fmapM_maybe,
         orElse,
         mapCatMaybes,
         allMaybes,
-        firstJust,
+        firstJust, firstJusts,
         expectJust,
         maybeToBool,
 
@@ -45,12 +46,14 @@ allMaybes (Just x  : ms) = case allMaybes ms of
                            Nothing -> Nothing
                            Just xs -> Just (x:xs)
 
+firstJust :: Maybe a -> Maybe a -> Maybe a
+firstJust (Just a) _ = Just a
+firstJust Nothing  b = b
+
 -- | Takes a list of @Maybes@ and returns the first @Just@ if there is one, or
 -- @Nothing@ otherwise.
-firstJust :: [Maybe a] -> Maybe a
-firstJust [] = Nothing
-firstJust (Just x  : _)  = Just x
-firstJust (Nothing : ms) = firstJust ms
+firstJusts :: [Maybe a] -> Maybe a
+firstJusts = foldr firstJust Nothing
 \end{code}
 
 \begin{code}
@@ -69,11 +72,20 @@ mapCatMaybes f (x:xs) = case f x of
 \end{code}
 
 \begin{code}
+
 orElse :: Maybe a -> a -> a
 (Just x) `orElse` _ = x
 Nothing  `orElse` y = y
 \end{code}
 
+\begin{code}
+fmapM_maybe :: Monad m => (a -> m b) -> Maybe a -> m (Maybe b)
+fmapM_maybe _ Nothing = return Nothing
+fmapM_maybe f (Just x) = do
+        x' <- f x
+        return $ Just x'
+\end{code}
+
 %************************************************************************
 %*									*
 \subsection[MaybeT type]{The @MaybeT@ monad transformer}