Question

我试图检查两个列表是否有相同的元素。

Example : 
List1 = ["John", "Thomas", "Sinclair", "Marie"]
List2 = ["Philip", "Albert", "Maria"]

结果应该是假的。

但如果是这样的话：

List3 = ["John", "Thomas", "Sinclair", "Marie"]
List4 = ["Philip", "Albert", "Marie", "Edward"]

结果应该是真的，list3和list4有相同的，＆＃34; Marie＆＃34;。

我的代码：

import qualified Data.Text    as Text
import qualified Data.Text.IO as Text

main = do
    list1 <- fmap Text.lines (Text.readFile "file1.txt")
    list2 <- fmap Text.lines (Text.readFile "file.txt")
    compareList list1 list2

compareList (x:xs) ys | elem x ys = True
                      |otherwise = compareList xs ys

result = 
if ((compareList list1 list2) == True)
       then putStrnLn ( " They sare elements")
          else
             putStrnLn ("They don't share elements")

我完全输了，代码无法编译。

Answer 1

您可以按照intersect和null定义此功能，如下所示：

compareList :: (Eq a) => [a] -> [a] -> Bool
compareList a = not . null . intersect a

Live demo

您的代码未编译，因为：

您在result
list1和list2未在result
putStrnLn不存在;你可能意味着putStrLn
您在compareList中呼叫main，其中Bool，而不是IO ()
您需要在(Eq a) =>以及compareList

result

如果你遵循这些建议，你会得到：

compareList :: (Eq a) => [a] -> [a] -> Bool
compareList [] _ = False
compareList (x:xs) ys 
    | elem x ys = True
    | otherwise  = compareList xs ys

result :: (Eq a) => [a] -> [a] -> IO ()
result list1 list2 = 
    if (compareList list1 list2)
        then putStrLn ("They share elements")
        else putStrLn ("They don't share elements")

Live demo

Answer 2

如果没有显式递归，您可以使用此

compareList :: (Eq a) => [a] -> [a] -> Bool
compareList xs ys = foldl (\acc x -> x `elem` ys || acc) False xs

检查2列表是否有任何相同的元素Haskell

2 个答案: