I am trying to change the Film type to a data type so it will make it easier to order and save and load to a file, I am having problems matching the functions up with the right arguments, it was a lot easier working with the types.
type Rating = (String, Int)
--type Film = (String, String, Int, [Rating])
data Film = Film String String Int [Rating]
deriving (Show,Ord,Eq, Read)
testDatabase :: [Film]
testDatabase = []
testFilm = ("Test","Test",2012,[("Test",8),("Test",5)])
saveToFile :: IO ()
saveToFile = do
putStrLn "Enter the output filename: "
name <- getLine
writeFile name (show testDatabase)
putStrLn "Done"
loadFromFile :: IO ()
loadFromFile = do
putStrLn "Enter the input filename: "
name <- getLine
contents <- readFile name
let testDatabase = length contents `seq` (read contents :: [Film])
putStrLn formatDatabase
putStrLn "Done"
average xs = realToFrac (sum xs) / genericLength xs
addFilm :: String -> String -> Int -> [Film] -> [Film]
addFilm title director year db = db ++ Film title director year []
filmsByDirector :: String -> [Film]
filmsByDirector name = filter (\(a,_,_,_) -> a == name) testDatabase
filmsByRating :: Float -> [Film]
filmsByRating rating = filter (\(_,_,_,a) -> filmRating a > rating) testDatabase
filmsByYear :: Int -> [Film]
filmsByYear year = filter (\(_,_,a,_) -> a == year) testDatabase
filmRating :: [(String,Int)] -> Float
filmRating ratings = average (map snd ratings)
formatString :: Film -> String
formatString (dir, film, year, rat) = printf "\n\nDirector: %s \nFilm Name: %s \nYear: %s \nRating: %4.2f" (show dir) (show film) (show year) (filmRating rat)
formattedByYear :: Int -> String
formattedByYear year = concatMap formatString $ filmsByYear year
formattedByDirector :: String -> String
formattedByDirector dir = concatMap formatString $ filmsByDirector dir
formatDatabase = concatMap formatString $ testDatabase
There isn't much to necessarily change, instead of
filmsByDirector name = filter (\(a,_,_,_) -> a == name) testDatabase
where you use the (,,,)
constructor for the pattern, you use the Film
constructor
filmsByDirector name = filter (\(Film a _ _ _) -> a == name) testDatabase
and similarly for the other functions.
However, it's much more convenient to use named-field (or record) syntax and define
data Film = Film { director, title :: String, year :: Int, ratings :: [Rating] }
and then the function would be simply
filmsByDirector name = filter ((name ==) . director) testDatabase
or, if you're uncomfortable with point-free style
filmsByDirector name = filter (\f -> director f == name) testDatabase
For the error regarding Film
vs [Film]
in addFilm
, you have to wrap the last film into []
,
addFilm title director year db = db ++ [Film title director year []]
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