[Haskell-cafe] efficient chop

Hello Cafe, I would like to have an efficient implementation of the chop function. As you guess, the chop function drops spaces in the tail of a list. chop " foo bar baz " -> " foo bar baz" A naive implementation is as follows: chopReverse :: String -> String chopReverse = reverse . dropWhile isSpace . reverse But this is not elegant. foldr version is as follows: chopFoldr :: String -> String chopFoldr = foldr f [] where f c [] | isSpace c = [] | otherwise = c:[] f c cs = c:cs But this code is slower than chopReverse in some cases. Are there any more efficient implementations of chop? Any suggestions? --Kazu