[project @ 1997-05-18 04:56:05 by sof]

new function: mapMaybe

diff --git a/ghc/compiler/utils/Maybes.lhs b/ghc/compiler/utils/Maybes.lhs
index a3834fd..2542141 100644 (file)
--- a/ghc/compiler/utils/Maybes.lhs
+++ b/ghc/compiler/utils/Maybes.lhs
@@ -12,6 +12,7 @@ module Maybes (
 --     Maybe(..), -- no, it's in 1.3
        MaybeErr(..),
 
+       mapMaybe,
        allMaybes,
        firstJust,
        expectJust,
@@ -80,6 +81,12 @@ allMaybes (Nothing : ms) = Nothing
 allMaybes (Just x  : ms) = case (allMaybes ms) of
                             Nothing -> Nothing
                             Just xs -> Just (x:xs)
+
+mapMaybe :: (a -> Maybe b) -> [a] -> [b]
+mapMaybe f [] = []
+mapMaybe f (x:xs) = case f x of
+                       Just y  -> y : mapMaybe f xs
+                       Nothing -> mapMaybe f xs
 \end{code}
 
 @firstJust@ takes a list of @Maybes@ and returns the