[project @ 2003-08-20 15:06:23 by simonmar]

Define maybePrefixMatch, which is like prefixMatch but returns the
rest of the String after the match.

diff --git a/ghc/compiler/utils/Util.lhs b/ghc/compiler/utils/Util.lhs
index f335062..28880a2 100644 (file)
--- a/ghc/compiler/utils/Util.lhs
+++ b/ghc/compiler/utils/Util.lhs
@@ -34,7 +34,7 @@ module Util (
 
        -- comparisons
        eqListBy, equalLength, compareLength,
-       thenCmp, cmpList, prefixMatch, suffixMatch,
+       thenCmp, cmpList, prefixMatch, suffixMatch, maybePrefixMatch,
 
        -- strictness
        foldl', seqList,
@@ -732,6 +732,13 @@ prefixMatch _pat [] = False
 prefixMatch (p:ps) (s:ss) | p == s    = prefixMatch ps ss
                          | otherwise = False
 
+maybePrefixMatch :: String -> String -> Maybe String
+maybePrefixMatch []    rest = Just rest
+maybePrefixMatch (_:_) []   = Nothing
+maybePrefixMatch (p:pat) (r:rest)
+  | p == r    = maybePrefixMatch pat rest
+  | otherwise = Nothing
+
 suffixMatch :: Eq a => [a] -> [a] -> Bool
 suffixMatch pat str = prefixMatch (reverse pat) (reverse str)
 \end{code}