检查2 list是否有任何相同的元素Haskell

Question

我试着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 e list4有同样的，"Marie“。

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")

我完全迷路了，代码不编译。

Answer 1

如果不使用显式递归，则可以使用以下方法

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