On Wed, 16 May 2007, Evan Laforge wrote: > > I think that in every particular case you have to find out how to avoid > > 'reverse'. Especially if you have two 'reverse's like in > > reverse . dropWhile p . reverse > > there are more efficient solutions. > > Just from curiosity, what *is* an efficient way to do rDropWhile? > Here's something which at least avoids 2 reverses: > > rDropWhile = doRDropWhile [] > > doRDropWhile accum f [] = [] > doRDropWhile accum f (x:xs) > | f x = doRDropWhile (x:accum) f xs > | otherwise = reverse (x:accum) ++ doRDropWhile [] f xs
http://www.haskell.org/pipermail/libraries/2005-August/004217.html dropWhileRev :: (a -> Bool) -> [a] -> [a] dropWhileRev p = foldr (\x xs -> if p x && null xs then [] else x:xs) [] _______________________________________________ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
