# Pastebin vXKCVFzi
{-# LANGUAGE AllowAmbiguousTypes #-}
{-# LANGUAGE RecordWildCards #-}
{-# LANGUAGE TypeApplications #-}
{-# LANGUAGE TypeFamilies #-}

import Control.Lens
import Data.Word

data Colour = Colour Word8 Word8 Word8

type family QualityType q

-- Typelevel tag
data ForegroundColour

type instance QualityType ForegroundColour = Colour

class HasQuality q s where
  -- could take a proxy argument here if you don't want to use
  -- AllowAmbiguousTypes and TypeApplications
  quality :: Lens' s (QualityType q)

data SomeRecord = SomeRecord
  { name :: String,
    fg :: Colour
  }

instance HasQuality ForegroundColour SomeRecord where
  quality f r@SomeRecord {..} = f fg <&> \fg' -> r {fg = fg'} -- or use a generated lens

whiteout :: HasQuality ForegroundColour a => a -> a
whiteout a = a & quality @ForegroundColour .~ Colour 255 255 255