Re: [Haskell-cafe] displaying conetents of a list
Even more succinctly: sequence_ . map is mapM_, and putStrLn . show is print, so you get: mapM_ print films Dan On Sun, May 10, 2009 at 9:59 PM, Alex MDC wrote: > 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 > > > ___ > Haskell-Cafe mailing list > Haskell-Cafe@haskell.org > http://www.haskell.org/mailman/listinfo/haskell-cafe > > ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] displaying conetents of a list
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 ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
[Haskell-cafe] displaying conetents of a list
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"]) ] --- 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.html Sent from the Haskell - Haskell-Cafe mailing list archive at Nabble.com. ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
