[Haskell-cafe] reversing big list with constant heap space used

[Evan Laforge]

> 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


I assume this is not in Data.List to discourage people from doing
things to the right side of lists...  it's still useful for string
stuff where ByteString would be overkill though.