Nested Maybe Accessor (Haskell)

Lens.hs

{-# LANGUAGE TemplateHaskell #-}

import Control.Lens

data Parent = Parent {
  _child :: Maybe Child
} deriving (Show)

data Child = Child {
  _property :: Maybe String
} deriving (Show)

p :: Parent
p = Parent {
  _child = Just Child {
    _property = Just "hello!"
  }
}

makeLenses ''Parent
makeLenses ''Child

m = _Just

(.?) a b = a . _Just . b

main :: IO ()
main = do
  print p
  print $ p^.child.m.property
  print $ p^.child.?property