从maybe列表中提取值列表而不是仅仅

Question

输入：[Just "foo", Just "bar", Nothing, Just "quux"]

输出：["foo", "bar", "quux"]

我对使用fromJust的以下解决方案不满意，因为它对 elm 不太容易移植，它不喜欢不安全的函数：

extract list = map fromJust $ filter isJust list

是否有另一种简洁/惯用的方法来实现这一目标？

Answer 1

您可以使用catMaybes：

import Data.Maybe
catMaybes list

Answer 2

Λ: :m + Data.Maybe
Λ: concatMap maybeToList [Just "foo", Just "bar", Nothing, Just "quux"]
["foo","bar","quux"]