lens-op-ob-lenses.hs

-- | A lens from a User to Text.
--
-- Written quite explicitly with getter and setter helper functions to expose
-- Lens's nature.
userName :: Lens' User UserName
userName = lens getter setter
  where
    getter user = _userName user
    setter user newName = user { _userName = newName }

score :: Lens' User Int
score = lens _userScore (\user newScore -> user { _userScore = newScore })

-- | Note that this lens targets a 'Maybe Pet'.
pet :: Lens' User (Maybe Pet)
pet = lens _userPet (\user maybePet -> user {_userPet = maybePet})

-- | Single letter vars, seriously? Yep.
inventory :: Lens' User Inventory
inventory = lens _userInventory (\u i -> u { _userInventory = i })

------------------------------------------------------------------------------

petName :: Lens' Pet PetName
petName = lens _petName (\p n -> p { _petName = n })

------------------------------------------------------------------------------

value :: Lens' Item Int
value = lens _itemValue (\i v -> i { _itemValue = v })

weight :: Lens' Item Int
weight = lens _itemWeight (\i w -> i { _itemWeight = w })