Hannah Schroeter wrote:
>
> Hello!
>
> On Mon, May 31, 1999 at 06:01:31PM +0200, Friedrich Dominicus wrote:
> > Hannah Schroeter wrote:
>
> > > Hello!
>
> > > On Fri, May 28, 1999 at 08:00:27AM +0200, Friedrich Dominicus wrote:
> > > > I wrote before with my trouble understanding hugsIsEOF. But I don't have
> > > > found a clean way just to write a cat. Can s.o give me a hand?
>
> > > import System(getArgs)
> > > file2stdout :: String {- filename -} -> IO ()
>
> > could you explain that to me?
>
> "{- filename -}" is just a comment designating that that parameter
> shall be the filename of the file to be copied to stdout.
Oh mei, just a comment it's time for me to reread my book it should be
found there.
>
> > If I want to do it line-by-line is is some combination from
> > getLine, putStr ?
>
> If you want to do it line wise, you probably have to do some
> exception handling in the IO monad. I.e. you try to read a line,
> handle the EOF exception by just terminating, any other exception
> by re-throwing it. If getLine succeeds you output it and continue,
> using tail recursion.
>
> That's something like this:
>
> import IO (isEOFError,openFile,IOMode(ReadMode),hGetLine)
>
> file2stdout filename = catch mainloop handler
> where
> mainloop = do
> handle <- openFile filename ReadMode
> mainloop' handle
> mainloop' hdl = do
> line <- hGetLine hdl
> putStrLn line
> mainloop' hdl
> handler err = if isEOFError err then return () else ioError err -- rethrow
>
> But why make it difficult if there's readFile?
I want to do the following, read a file line by line and finding out
which line is longer than x-chars. I want to print out which lines are
so long. I think that can just be done line-wise.
Thanks for you answer I hope I got it right with that information.
Regards
Friedrich
