I am wondering if there is a function in haskell to determine if each element in a list is in another list. I wrote my own, but it seems like something that would be in Prelude or Data.List

each :: Eq a => [a] -> [a] -> Bool
each xs ys = foldl (\acc x -> if x `elem` ys then True && acc else False) True xs

Does something like this already exist?

CodePudding user response：

The set operation you want specifically is not in the Prelude, but all makes the definition somewhat trivial (though not necessarily efficient).

-- Check if every element in xs is in ys (i.e., is xs a subset of ys)
each xs ys = all (`elem` ys) xs

Assuming your lists do not have duplicate values, you might try (\\).

import Data.List

-- Check if removing all elements in ys from xs produces an empty list.
each xs ys = null (xs \\ ys)