Re: [Haskell-cafe] haskell - main function

9 May 2009

      Hi

applebiz89 wrote:
...
Could anyone look at this segment of code; it's not compiling wondering if
anyone could correct me as to why. Thanks
Code:
-- 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 -> 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
main :: [Film] -> IO()
main db = 
  do putStr "Hi there! what is your name: "
     fanName = getLine
     do 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
        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 <- getLine
            main insertFilm [Title Director Year [Film]]
        else if x == 2
         then do putStr "Enter film title: "
              filmTitle <- getLine
              putStr "Enter fan name: "
              fanName <- getLine
              main becomeFan [Title fanName]
        else if x == 3
         then do putStr "Enter film title: "
              filmTitle <- getLine
              main numberOfFans [Title]
        else if x == 4
         then do putStr "Enter film release year: "
      	filmYear <- getLine
      	main filmsInGivenYear [Year [Film]]
        else if x == 5
         then do putStr "Enter the fan name: "
      	fanName <- getLine
      	main givenUser [fanName [Film]]
        else if x = 6
         then return ()
You have an if without an else. You cannot have that. What should the
program do when x /= 6. And you write "x = 6" in stead of "x == 6".

But generally speaking, you want to include compiler output in "this is
not compiling"-messages to haskell-cafe.

Regards,

Mads Lindstrøm