haskell中的列表降序​​排序

Question

我試圖給出在給定年份或之後發佈的所有電影，按照網站評級的降序排列。

我設法做出一個函數來返回平均評分和函數來過濾數據庫並返回給定年份的電影。

這裏的問題是如何將這兩個放在一起，並按降序排序。我不太確定或熱衷於此，需要一些幫助。

import Data.List 
import Text.Printf 
import Data.Ord 

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

testDatabase :: [Film] 
testDatabase = [("Blade Runner","Ridley Scott",1982,[("Amy",6), ("Bill",9), ("Ian",7), ("Kevin",9), ("Emma",4), ("Sam",5), ("Megan",4)]), 
       ("The Fly","David Cronenberg",1986,[("Megan",4), ("Fred",7), ("Chris",5), ("Ian",0), ("Amy",5)]), 
       ("Psycho","Alfred Hitchcock",1960,[("Bill",4), ("Jo",4), ("Garry",8), ("Kevin",7), ("Olga",8), ("Liz",10), ("Ian",9)]), 
       ("Body Of Lies","Ridley Scott",2008,[("Sam",3), ("Neal",7), ("Kevin",2), ("Chris",5), ("Olga",6)]), 
       ("Avatar","James Cameron",2009,[("Olga",2), ("Wally",8), ("Megan",9), ("Tim",5), ("Zoe",8), ("Emma",3)]), 
       ("Titanic","James Cameron",1997,[("Zoe",7), ("Amy",2), ("Emma",5), ("Heidi",3), ("Jo",8), ("Megan",5), ("Olga",7), ("Tim",10)]), 
       ("The Departed","Martin Scorsese",2006,[("Heidi",2), ("Jo",8), ("Megan",5), ("Tim",2), ("Fred",5)]), 
       ("Aliens","Ridley Scott",1986,[("Fred",8), ("Dave",6), ("Amy",10), ("Bill",7), ("Wally",2), ("Zoe",5)]), 
       ("Prometheus","Ridley Scott",2012,[("Garry",3), ("Chris",4), ("Emma",5), ("Bill",1), ("Dave",3)]), 
       ("E.T. The Extra-Terrestrial","Steven Spielberg",1982,[("Ian",7), ("Amy",2), ("Emma",7), ("Sam",8), ("Wally",5), ("Zoe",6)]), 
       ("The Birds","Alfred Hitchcock",1963,[("Garry",7), ("Kevin",9), ("Olga",4), ("Tim",7), ("Wally",3)]), 
       ("Goodfellas","Martin Scorsese",1990,[("Emma",7), ("Sam",9), ("Wally",5), ("Dave",3)]), 
       ("The Shawshank Redemption","Frank Darabont",1994,[("Jo",8), ("Sam",10), ("Zoe",3), ("Dave",7), ("Emma",3), ("Garry",10), ("Kevin",7)]), 
       ("Gladiator","Ridley Scott",2000,[("Garry",7), ("Ian",4), ("Neal",6), ("Wally",3), ("Emma",4)]), 
       ("The Green Mile","Frank Darabont",1999,[("Sam",3), ("Zoe",4), ("Dave",8), ("Wally",5), ("Jo",5)]), 
       ("True Lies","James Cameron",1994,[("Dave",3), ("Kevin",4), ("Jo",0)]), 
       ("Minority Report","Steven Spielberg",2002,[("Dave",5), ("Garry",6), ("Megan",2), ("Sam",7), ("Wally",8)]), 
       ("The Wolf of Wall Street","Martin Scorsese",2013,[("Dave",6), ("Garry",6), ("Megan",0), ("Sam",4)]), 
       ("War Horse","Steven Spielberg",2011,[("Dave",6), ("Garry",6), ("Megan",3), ("Sam",7), ("Wally",8), ("Zoe",8)]), 
       ("Lincoln","Steven Spielberg",2012,[("Ian",3), ("Sam",7), ("Wally",3), ("Zoe",4), ("Liz",7), ("Megan",4)]), 
       ("Vertigo","Alfred Hitchcock",1958,[("Bill",7), ("Emma",5), ("Zoe",9), ("Olga",6), ("Tim",10)]), 
       ("The Terminal","Steven Spielberg",2004,[("Olga",3), ("Heidi",8), ("Bill",2), ("Sam",6), ("Garry",8)]), 
       ("Jaws","Steven Spielberg",1975,[("Fred",3), ("Garry",0), ("Jo",3), ("Neal",9), ("Emma",7)]), 
       ("Hugo","Martin Scorsese",2011,[("Sam",4), ("Wally",3), ("Zoe",4), ("Liz",7)])]  

averageFilmRating :: [(String,Int)] -> Float 
averageFilmRating ratings 
    = (fromIntegral(sum $ map snd ratings))/(fromIntegral(length ratings)) 

--Displays films by year 
filmsByYear :: Int -> [Film] 
filmsByYear year 
    = filter(\(_,_,yr,_) -> yr >= year) testDatabase  

Answer 1

import Data.List 
import Data.Ord 

sortFilms :: [Film] -> [Film] 
sortFilms = sortBy $ flip $ comparing averageFilmRating' 
    where 
    averageFilmRating' (_,_,_,rs) = averageFilmRating rs