小编use*_*712的帖子

import Data.Char

-- Sample test data
testData :: [Movies]
testData = [("Me and My Broken Heart","Rixton"),
            ("It’s My Birthday","will.i.am"),
            ("Problem","Ariana Grande")]

-- record a sale of a track 
record :: [Movies] -> String -> String 
record t a = []
record ((t, a): xs) a a
    | t == a && a == a = [(t,a)]
    | otherwise = record xs a t

正确的输出应该是数据库的修改版本.

import Data.Char
import Data.List
import Data.Maybe

-- Sample test data
type Movies = (String, String)

sample :: [Movies]
sample = [("I am legend","Will Smith"),
        ("Rise of the Planet of the Apes","James Franco"),
        ("Godzilla","Bryan Cranston")]

sellTicket :: [Movies] -> String -> String -> [Movies]
sellTicket [] _ _ = []
sellTicket ((title, actor): xs) aTitle anActor
    | title == aTitle && actor == anActor = 
        (title, actor):sellTicket xs aTitle anActor
    | otherwise = (title,actor):sellTicket xs aTitle anActor

谢谢大家的帮助,现在一切正常.

而詹姆斯弗兰科则崛起了猿星球.

如何根据第一个元素或第二个或第三个元素搜索元组？

我知道如何搜索两个元组,但我怎么做两个以上呢？

type Stuff = (String, String, Int)

testStuff :: [Stuff]
testStuff = [
    ("beans","black",5),
    ("cod","fish",4),
    ("coke","diet",3)
]

如何编写一个搜索"Stuff"并返回"int"值的函数？

例如,searchStuff"beans"应该返回5.