Right, but if you use Prelude.interact, as in my example, you don't have to
worry about the EOF checking yourself - it's all handled for you. And if you
use a functional style, your code will be simpler and more testable - otherwise
you might as well just use an imperative language.
Here's a slightly better version (uses splitAt):
maxLineLength :: Int
maxLineLength = 72
wrapLine :: String -> [String]
wrapLine "" = []
wrapLine line
| length line <= maxLineLength = [line]
| otherwise = let (line, rest) =
splitAt maxLineLength line in
line :
wrapLine rest
main :: IO ()
main = interact $ unlines . concatMap wrapLine . lines
On Saturday Aug 14, 2010, at 12:38 AM, michael rice wrote:
> Hi Bill,
>
> Each quote of the input is on a single line. I want to unwrap lines greater
> than 72 characters, i.e., break them into several lines each <= 72
> characters, but I don't want to break up words. and I want to retain the
> blank lines. So, my output is correct except for the error message.
>
> Michael
>
> ============ My input data ============
> 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 trouble
> yourself much to get new things, whether clothes or friends. Things do not
> change, we change. Sell your clothes and keep your thoughts. God 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 man to
> elevate his life by conscious endeavor.
>
> I once had a sparrow alight upon my shoulder for a moment, while I was hoeing
> in a village garden, and I felt that I was more distinguished by that
> circumstance that I should have been by any epaulet I could have worn.
>
> -Thoreau
> ============ My output ============
> unwrap: <stdin>: hGetLine: end of file <<<< here's my eof message
> 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
> trouble yourself much to get new things, whether clothes or friends.
> Things do not change, we change. Sell your clothes and keep your
> thoughts. God 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
> man to elevate his life by conscious endeavor.
>
> I once had a sparrow alight upon my shoulder for a moment, while I was
> hoeing in a village garden, and I felt that I was more distinguished by
> that circumstance that I should have been by any epaulet I could have
> worn.
>
> -Thoreau
> ============ Your 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
> ===================================
>
>
> --- On Fri, 8/13/10, Bill Atkins <watk...@alum.rpi.edu> wrote:
>
> From: Bill Atkins <watk...@alum.rpi.edu>
> Subject: Re: [Haskell-cafe] Unwrapping long lines in text files
> To: "michael rice" <nowg...@yahoo.com>
> Cc: haskell-cafe@haskell.org
> Date: Friday, August 13, 2010, 11:13 PM
>
> Not sure if I understood what you're trying to do, but development will be
> easier if you minimize your IO, e.g. :
>
> maxLineLength :: Int
> maxLineLength = 72
>
> wrapLine :: String -> [String]
> wrapLine "" = []
> wrapLine line
> | length line <= maxLineLength = [line]
> | otherwise = take maxLineLength
> line : wrapLine (drop maxLineLength line)
>
> main :: IO ()
> main = interact $ unlines . concatMap wrapLine . lines
>
> Now wrapLine is pure and you can use it more easily using GHCi. Removing
> dependencies on IO usually makes your problem easier to test and understand
> and your code simpler.
>
> In your example, the EOF probably happens on the call to getLine after input
> has run out. By using Prelude.interact, we can ignore details like that and
> rely on already-written functions.
>
> HTH,
> Bill
>
> On Friday Aug 13, 2010, at 9:38 PM, michael rice wrote:
>
> > The program below takes a text file and unwraps all lines to 72 columns,
> > but I'm getting an end of file message at the top of my output.
> >
> > How do I lose the EOF?
> >
> > Michael
> >
> >
> > ====== unwrap.hs ======
> >
> > main = do
> > line <- getLine
> > if null line
> > then do
> > putStrLn ""
> > main
> > else
> > do
> > printList (words line) 1
> > main
> >
> >
> > printList :: [String] -> Int -> IO ()
> > printList [] _ = do putStrLn ""
> > printList (w:[]) k = do
> > if k+(length w) <= 72
> > then do
> > putStrLn w
> > else do
> > putStrLn ""
> > putStrLn w
> > printList r@(w:ws) k = do
> > if k+(length w) <= 72
> > then do
> > putStr w
> > putStr " "
> > printList ws (k+(length w)+1)
> > else do
> > putStrLn ""
> > printList r 1
> >
> >
> >
> > _______________________________________________
> > Haskell-Cafe mailing list
> > Haskell-Cafe@haskell.org
> > http://www.haskell.org/mailman/listinfo/haskell-cafe
>
>
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