Haskell中的电影数据库
问题描述：
目前正在尝试解决我的haskell计划中的两个主要问题。
Currently trying to solve 2 main questions in my haskell program.
- 显示给定用户是
-
- 显示特定演员在
特定时期（即指定开始年份和结束年份）之间发布的所有电影
这是我目前使用的示例数据库：
This is the sample database I am currently using:
type Title = String
type Cast = String
type Year = Int
type Fans = String
type Film = (Title, [Cast], Year, [Fans])
type Database = [Film]
testDatabase :: Database
testDatabase = [("Casino Royale", ["Daniel Craig", "Eva Green", "Judi Dench"], 2006, ["Garry", "Dave", "Zoe", "Kevin", "Emma"]),
("Cowboys & Aliens", ["Harrison Ford", "Daniel Craig", "Olivia Wilde"], 2011, ["Bill", "Jo", "Garry", "Kevin", "Olga", "Liz"]),
("Catch Me If You Can", ["Leonardo DiCaprio", "Tom Hanks"], 2002, ["Zoe", "Heidi", "Jo", "Emma", "Liz", "Sam", "Olga", "Kevin", "Tim"])]
数据库大得多，但由于空间原因，我省略了一些。
The database is much bigger but for space reasons I omitted some of this.
- 如何使用此数据库创建回答上述两个问题所需的函数？
答
这应该工作：
type Title = String
type Actor = String
type Cast = [Actor]
type Year = Int
type Fan = String
type Fans = [Fan]
type Period = (Year, Year)
type Film = (Title, Cast, Year, Fans)
type Database = [Film]
testDatabase :: Database
testDatabase = [("Casino Royale", ["Daniel Craig", "Eva Green", "Judi Dench"], 2006, ["Garry", "Dave", "Zoe", "Kevin", "Emma"]),
("Cowboys & Aliens", ["Harrison Ford", "Daniel Craig", "Olivia Wilde"], 2011, ["Bill", "Jo", "Garry", "Kevin", "Olga", "Liz"]),
("Catch Me If You Can", ["Leonardo DiCaprio", "Tom Hanks"], 2002, ["Zoe", "Heidi", "Jo", "Emma", "Liz", "Sam", "Olga", "Kevin", "Tim"])]
inCast :: Actor -> Film -> Bool
inCast givenActor (_, cast, _, _) = any (\actor -> actor == givenActor) cast
inPeriod :: Period -> Film -> Bool
inPeriod (periodStart, periodEnd) (_, _, year, _) = periodStart <= year && year <= periodEnd
inCastAndPeriod :: Actor -> Period -> Film -> Bool
inCastAndPeriod actor period film = inCast actor film && inPeriod period film
isFan :: Fan -> Film -> Bool
isFan givenFan (_, _, _, fans) = any (\fan -> fan == givenFan) fans
allFilmsThatAGivenUserIsAFanOf :: Fan -> [Film]
allFilmsThatAGivenUserIsAFanOf givenFan = filter (isFan givenFan) testDatabase
allTheFilmsOfAGivenActorThatWereReleasedDuringAParticularPeriod :: Actor -> Period -> [Film]
allTheFilmsOfAGivenActorThatWereReleasedDuringAParticularPeriod givenActor givenPeriod = filter (inCastAndPeriod givenActor givenPeriod) testDatabase