2009/5/11 applebiz89

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, Alex

listFilms = [Film] -> IO () listFilms = putStrLn . show -- point free style listFilms films = putStrLn $ show films listFilms = mapM_ (putStrLn . show) -- put each movie on a separate line, point free style listFilms films = mapM_ (putStrLn . show) films Hope that makes sense... Michael On Sun, May 10, 2009 at 5:30 PM, applebiz89 wrote:

I want to write a function to output the entire contents of a list. not sure of how to do so...This is my list i want to output

type Title = String type Director = String type Year = Int type Fan = String

data Film = Film Title Director Year [Fan] deriving Show

-- List of films

testDatabase :: [Film] testDatabase = [(Film "Casino Royale" "Martin Campbell" 2006 ["Garry", "Dave", "Zoe"]) ]

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I know this isnt right but this is what I have so far

listFilms :: [Film] -> [Film] listFilms (film@(Film title director year fans) : films) = putStrLn . show film

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

thank you. -- View this message in context: http://www.nabble.com/displaying-conetents-of-a-list-tp23470633p23470633.htm... Sent from the Haskell - Haskell-Cafe mailing list archive at Nabble.com.

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