On Tue, May 12, 2009 at 9:59 AM, applebiz89 wrote:

I have compiled each function independently and they have compiled the only problem is the main function..

I keep getting the error 'films not defined' and I am not sure why

[code]

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"])]

-- Function

filmsInGivenYear :: Year -> [Film] -> [String] filmsInGivenYear year' films = [ title | (Film title director year fans) <- films, year == year']

doFilmsInGivenYear :: [Film] -> IO () doFilmsInGivenYear films  = do putStrLn "which year?"                               text <- getLine                               let year' = read text :: Int                               let answer = filmsInGivenYear year' films                               print answer

main :: IO () main = do         doFilmsInGivenYear films         main

[/code]

if the other functions are compiling without this error im not sure as to why the main function does not compile because of the films...any light on this?

Thanks

When you say 'doFilmsInGivenYear films', where does the variable 'films' come from? It's not defined anywhere in your program. That's what the compiler is complaining about. Alex

Am Dienstag 12 Mai 2009 18:59:47 schrieb applebiz89:

I have compiled each function independently and they have compiled the only problem is the main function..

I keep getting the error 'films not defined' and I am not sure why

[code]

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"])]

-- Function

filmsInGivenYear :: Year -> [Film] -> [String] filmsInGivenYear year' films = [ title | (Film title director year fans) <- films, year == year']

doFilmsInGivenYear :: [Film] -> IO () doFilmsInGivenYear films = do putStrLn "which year?" text <- getLine let year' = read text :: Int let answer = filmsInGivenYear year' films print answer

main :: IO () main = do doFilmsInGivenYear films main

There is no top level definition of films in your module, main doesn't take any parameter, so films is not in scope in main. You probably meant testDatabase. However, main is not good even if you fix that, because every iteration of main, you work on the same database, you can't add new films or fans to films. You should do something like main :: IO () main = loop testDatabase loop db = do actionToRun <- selectAction newDB <- actionToRun db loop newDB selectAction = do putStrLn $ "Select action to run:\n 1-print films from given year\n 2-add fan for some film\n ..." ln <- getLine let n = read ln act = case n of 1 -> doFilmsInGivenYear 2 -> becomeFan .... return act doFilmInGivenYear :: [Film] -> IO [Film] doFilmInGivenYear films = do .... (your code) return films becomeFan :: [Film] -> IO [Film] becomeFan films = do who <- ask for name of fan whichFilm <- ask for film let newFilms = makeFan who whichFilm films return newFilms then you can alter your database and have the modified database available in the next iteration of loop.

[/code]

if the other functions are compiling without this error im not sure as to why the main function does not compile because of the films...any light on this?

The other functions receive films as a parameter.

Thanks