Try this one (http://gist.github.com/524460):
import Data.Char
maxLineLength :: Int
maxLineLength = 72
trim :: String -> String
trim = reverse . dropSpaces . reverse . dropSpaces
where dropSpaces = dropWhile isSpace
none :: (a -> Bool) -> [a] -> Bool
none f = not . any f
reverseBreak :: (a -> Bool) -> [a] -> ([a], [a])
reverseBreak f xs = (reverse before, reverse after)
where (after, before) = break f $ reverse xs
wrapLine :: String -> [String]
wrapLine "" = [[]]
wrapLine line
| length line <= maxLineLength = [line]
| none isSpace line = beforeMax : wrapLine afterMax
| otherwise = beforeSpace : (wrapLine $ afterSpace ++
afterMax)
where (beforeMax, afterMax) = splitAt maxLineLength line
(beforeSpace, afterSpace) = reverseBreak isSpace beforeMax
main :: IO ()
main = interact $ unlines . concatMap (map trim . wrapLine) . lines
On Saturday Aug 14, 2010, at 9:41 AM, michael rice wrote:
> Hi Filipe, Bill
>
> Your corrected version works, while the original didn't, but it still
> produces incorrect
> output:
>
> However mean your life is, meet it and live it: do not shun it and call
> it hard names. Cultivate poverty like a garden herb, like sage. Do not t
> rouble yourself much to get new things, whether clothes or friends. Thin
> gs do not change, we change. Sell your clothes and keep your thoughts. G
> od will see that you do want society.
> Men have become the tools of their tools.
> I know of no more encouraging fact than the unquestioned ability of a ma
> n to elevate his life by conscious endeavor.
> I once had a sparrow alight upon my shoulder for a moment, while I was h
> oeing in a village garden, and I felt that I was more distinguished by t
> hat circumstance that I should have been by any epaulet I could have wor
> n.
> -Thoreau
>
> I don't want to break lines in the middle of words and I want to retain the
> original structure of the text with respect to blank lines between individual
> quotes. THe only thing in the input text that should change are the lines
> longer than 72 characters, and they should be reformatted to one or more
> lines less than or equal to 72 characters.
>
> Michael
>
> --- On Sat, 8/14/10, Felipe Lessa <[email protected]> wrote:
>
> From: Felipe Lessa <[email protected]>
> Subject: Re: [Haskell-cafe] Unwrapping long lines in text files
> To: "Bill Atkins" <[email protected]>
> Cc: "michael rice" <[email protected]>, [email protected]
> Date: Saturday, August 14, 2010, 9:17 AM
>
> On Sat, Aug 14, 2010 at 9:59 AM, Bill Atkins <[email protected]> wrote:
> > | otherwise = let (line, rest) =
> > splitAt maxLineLength line in
> > line :
> > wrapLine rest
>
> I haven't tested myself, but does this work at all? If I am reading
> it correctly, this is the same as
>
> let (foo, rest) = splitAt maxLineLength foo
> in foo : wrapLine rest
>
> In other words, no mention of wrapLine's argument 'line', and a
> recursive call that will bottom out and be the same as 'undefined' :).
> GHC would warn you, though, if you used -Wall. That expression
> should read:
>
> let (thisLine, rest) = splitAt maxLineLength line
> in thisLine : wrapLine rest
>
> Cheers,
>
> --
> Felipe.
>
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