[Haskell-cafe] A round of golf

[Lennart Augustsson]

Without any fancy byte strings:

main = do
   name:_ <- getArgs
   file <- readFile name
   print $ length $ lines file


On Thu, Sep 18, 2008 at 6:02 PM, Creighton Hogg <wchogg at gmail.com> wrote:
> Hey Haskell,
> So for a fairly inane reason, I ended up taking a couple of minutes
> and writing a program that would spit out, to the console, the number
> of lines in a file.  Off the top of my head, I came up with this which
> worked fine with files that had 100k lines:
>
> main = do
>  path <- liftM head $ getArgs
>  h <- openFile path ReadMode
>  n <- execStateT (countLines h) 0
>  print n
>
> untilM :: Monad m => (a -> m Bool) -> (a -> m ()) -> a -> m ()
> untilM cond action val = do
>  truthy <- cond val
>  if truthy then return () else action val >> (untilM cond action val)
>
> countLines :: Handle -> StateT Int IO ()
> countLines = untilM (\h -> lift $ hIsEOF h) (\h -> do
>                                                lift $ hGetLine h
>                                                modify (+1))
>
> If this makes anyone cringe or cry "you're doing it wrong", I'd
> actually like to hear it.  I never really share my projects, so I
> don't know how idiosyncratic my style is.
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