[Haskell-cafe] Re: Software Tools in Haskell

[Conal Elliott]

Since there are many useful per-line functions, do a little refactoring,
placing the following into a library:

  perLine :: (String -> String) -> (String -> String)
  perLine f = unlines . map f . lines


On Dec 12, 2007 12:43 PM, apfelmus <apfelmus at quantentunnel.de> wrote:

> Tommy M McGuire wrote:
> > (Plus, interact is scary. :-D )
>
> You have a scary feeling for a moment, then it passes. ;)
>
> > Gwern Branwen wrote:
> >> I... I want to provide a one-liner for 'detab', but it looks
> >> impressively monstrous and I'm not sure I understand it.
> >
> > On the other hand, I'm not looking for one-liners; I really want clarity
> > as opposed to cleverness.
>
>   tabwidth = 4
>
>      -- tabstop !! (col-1) == there is a tabstop at column  col
>      -- This is an infinite list, so no need to limit the line width
>   tabstops  = map (\col -> col `mod` tabwidth == 1) [1..]
>
>      -- calculate spaces needed to fill to the next tabstop in advance
>   tabspaces = snd $ mapAccumR addspace [] tabstops
>   addspace cs isstop = let cs'=' ':cs in (if isstop then [] else cs',cs')
>
>
>   main = interact $ unlines . map detabLine . lines
>      where
>      detabLine = concat $ zipWith replace tabspaces
>      replace cs '\t' = cs     -- replace with adequate number of spaces
>      replace _  char = [char] -- pass through
>
>
> How about that?
>
>
> Regards,
> apfelmus
>
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