At Sat, 9 May 2009 04:54:13 -0700 (PDT), applebiz89 wrote:

Could anyone look at this segment of code; it's not compiling wondering if anyone could correct me as to why. Thanks

There is a ton of things wrong with that code. I have attached a version that at least compiles, but there are still a bunch of things that are wrong. -- Film as datatype type Title = String type Director = String type Year = Int type Fan = String data Film = Film Title Director Year [Fan] -- List of films testDatabase :: [Film] testDatabase = [(Film "Casino Royale" "Martin Campbell" 2006 ["Garry","Dave", "Zoe"]) ] becomeFan :: Title -> Fan -> [Film] -> [Film] becomeFan _ _ [] = [] becomeFan title' fanName (film@(Film title director year fans) : films) | title == title' = (Film title director year (fanName:fans)) : films | otherwise = film : becomeFan title' fanName films insertFilm = undefined numberOfFans = undefined filmsInGivenYear= undefined givenUser = undefined mainLoop :: [Film] -> IO() mainLoop db = do putStr "Hi there! what is your name: " fanName <- getLine putStr "1 = Insert film, 2 = Become a Fan, 3 = The number of fans of a film, 4 = Film released in a year, 5 = Given fan, 6 = Stop : " input <- getLine let x = read input :: Int if x == 1 then do putStr "Enter film title: " filmTitle <- getLine putStr "Enter director name: " filmDirector <- getLine putStr "Enter release year: " filmYear <- fmap read getLine mainLoop $ insertFilm (Film filmTitle filmDirector filmYear []) db else if x == 2 then do putStr "Enter film title: " filmTitle <- getLine putStr "Enter fan name: " fanName <- getLine mainLoop $ becomeFan filmTitle fanName db else if x == 3 then do putStr "Enter film title: " filmTitle <- getLine mainLoop $ numberOfFans filmTitle db else if x == 4 then do putStr "Enter film release year: " filmYear <- getLine mainLoop $ filmsInGivenYear filmYear db else if x == 5 then do putStr "Enter the fan name: " fanName <- getLine mainLoop $ givenUser fanName db else if x == 6 then return () else return () main :: IO () main = mainLoop testDatabase

applebiz89 wrote:

becomeFan :: Title -> fanName -> [Film] -> [Film] becomeFan _ _ [] = [] becomeFan Title fanName ((Film Title Director Year fan):xs) | filmName == title = (Film Title Director Year fanName:fan) : xs | otherwise = (Film Title Director Year fan) : becomeFan Title fanName xs

In the type signature, you have to use types. In other words, use "Fan" instead of "fanName" in the first line. Variables have to begin with a lowercase letter. In other words, use "title", "director", "year" instead of "Title", "Director", "Year". Regarding the IO: I still propose to get your pure functions to work first, then worry about IO. You can test your code by loading it into ghci.

ghci nameofmyfile.hs

If everything works (i.e. no compile errors), you can call your functions at the prompt:

becomeFan "Casine Royale" "apple", testDatabase

Now ghci should answer with something like the following: [(Film "Casino Royale" "Martin Campbell" 2006 ["apple", "Garry", "Dave", "Zoe"])] This way, you can test your stuff while working on it. Tillmann