[Haskell-cafe] displaying conetents of a list

Alex MDC alex.mdc at gmail.com
Sun May 10 21:59:18 EDT 2009

2009/5/11 applebiz89 <applebiz89 at hotmail.com>

> I know to use show and putStrLn but I just don't know how to put them into
> the function correctly

Well I hope we're not doing your homework for you but...

As putStrLn is in the IO monad, listFilms should at least have a signature
like this:

listFilms :: [Film] -> IO ()

Now you know you want to call putStrLn on each item in the list. That means
you want to join a bunch of functions return IO (). That sounds like a job
for sequence_:

listFilms films = sequence_ $ map (putStrLn.show) films

Or the same thing more verbosely:

listFilms [] = return ()
listFilms (film:films)
 = do putStrLn (show film)
      listFilms films

Hope that helps,
-------------- next part --------------
An HTML attachment was scrubbed...
URL: http://www.haskell.org/pipermail/haskell-cafe/attachments/20090510/44ee10d0/attachment.html

More information about the Haskell-Cafe mailing list