如何在不嵌套 Maybe 的情况下 "zoom" 通过多个 Maybe 级别？

Question

让我们

data B = B {_b :: Maybe Int} deriving (Eq, Show, Generic)
makeFieldsNoPrefix ''B

data A = A {_a :: Maybe B} deriving (Eq, Show, Generic)
makeFieldsNoPrefix ''A

现在我想从 A（Maybe Int in Maybe B）“放大”到 b。我想到了：

let _TEST :: Maybe Int = (A {_a = Just B{_b = Just 7}}) ^. a ^? _Just . b & join

是否可以使用一些镜头运算符直接获得 Maybe Int 而无需使用 join 从 Maybe (Maybe Int) 解压它？

Answer 1

_TEST ^? a . _Just . b . _Just

如何在不嵌套 Maybe 的情况下 "zoom" 通过多个 Maybe 级别？

How to "zoom" through multiple levels of Maybe without getting nested Maybes?

haskell

haskell-lens