[Haskell-beginners] movie database

[Payan Peshraw]

Hi, 

 

I have got a database with movies added into it. What Im basically coding is:

 

- add a new film to the database
- display all the films
- display all the films by a given director
- display a list of user ratings (together with the users' names) for a given film
- show the average overall rating for a given director
- allow a given user to rate (or re-rate) a film (note that only the latest rating from the user should remain recorded)
- display all the films from a given year, sorted in descending order of overall rating
 
Now I want to allow a given user to rate or be able to re-rate a film. But the latest rating from the user should remain recorder tho..and also I want to display all the films that a given user likes (i.e. the films to which she has given a positive-valued rating). I have written the code for the user liking the film but it doesn't seem to work and i'm not sure what to do with that one eiher.
 
Below is the coding that I've written so far, but i'm stuck on the last bit which I can't seem to code. 
 
 
type Director = String
type Title = String
type Year = Int
type Mark = Int
type Rating = (String, Int)

type Film = (Title, Director, Year, [Rating])
type Database = [Film]

testDatabase :: Database
testDatabase = [("Casino Royale", "Martin Campbell", 2006, [("Garry",-8),("Dave", 0)]), 
                ("Blade Runner", "Ridley Scott", 1982, [("Amy",5)]), 
    ("The Fly", "David Cronenberg", 1986, [("Fred",7)])
    ]

addFilm :: Database -> Title -> Director -> Year -> Database
addFilm  database title director year 
         = (title, director, year, []): database
 
displayFilms :: Database ->[(Title, Director, Year, Mark)]
displayFilms [] = []
displayFilms ((i, j, k, l):xs)
               |l == [] = (i, j, k, 0) : displayFilms xs
               |otherwise = (i, j, k, overallRating l) : displayFilms xs
 
overallRating :: [Rating] -> Int
overallRating rating = div (sum [j | (_,j) <- rating]) (length rating) 
 
filmsByDirector :: Database -> Director -> Database
filmsByDirector [] filmDirector = []
filmsByDirector((i, j, k, l):xs) filmDirector
                 |j == filmDirector = (i, j, k, l) : filmsByDirector xs filmDirector
                 |otherwise = filmsByDirector xs filmDirector
 
filmRating :: Database -> Title -> [Rating]
filmRating [] filmRat = []
filmRating ((i,j, k, l):xs) filmRat
                |i == filmRat = (l ++ filmRating xs filmRat)
                |otherwise = filmRating xs filmRat
 
 
THIS DOESNT SEEM TO WORK?
{-
filmsLiked :: Database -> String -> Database
filmsLiked [] user = []
filmsLiked ((i,j,k,l):xs) user
                 | == user = i ++ filmsLiked xs user
                 |otherwise = filmsLiked xs user
 
person :: [Rating] -> String -> Bool
person [] userName = False
person ((n, s):xs) userName
                    |n == userName && s > 0 = True
                    |otherwise = person xs userName
-}
 
averageDirector :: Database -> Director -> Int
averageDirector [] directorRating = 0
averageDirector ((i,j,k,l):xs) directorRating
                    |j == directorRating = (overallRating l) + (averageDirector xs directorRating)
                    |otherwise = averageDirector xs directorRating
 
filmFromYear :: Database -> Year -> Database
filmFromYear [] filmYear = []
filmFromYear ((i,j,k,l):xs) filmYear
                    |k == filmYear = (i,j,k,l) : filmFromYear xs filmYear
                    |otherwise = filmFromYear xs filmYear
 
rateFilm :: [Rating] -> Rating -> [Rating]
rateFilm [] rating = rating:[] 
rateFilm ((user, rating):xs) (newUser, newRating)
                    |newUser == user = ((newUser, newRating):xs)
                    |otherwise = (user, rating) : (rateFilm xs (newUser, newRating))
 
Stuck on this bit..
{- 
changeFilm :: Database -> Title -> [Rating] -> Database
changeFilm .........
-}
 
 
 
Any help is appreciated..thank you!
 		 	   		  
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