Overloading records with lens

gistfile1.hs

{-# LANGUAGE TemplateHaskell #-}
{-# LANGUAGE FunctionalDependencies #-}
{-# LANGUAGE FlexibleInstances #-}

module Fields where

import Control.Lens
import Control.Lens.TH

data Vec2 = Vec2
  { _vec2X :: Double
  , _vec2Y :: Double
  } deriving (Eq, Read, Show)

data Vec3 = Vec3
  { _vec3X :: Double
  , _vec3Y :: Double
  , _vec3Z :: Double
  } deriving (Eq, Read, Show)

makeFields ''Vec2
makeFields ''Vec3

-- results in: Vec2 2 2
example1 = over x (+1) $ Vec2 1 2
-- results in: Vec3 1 2 300
example2 = over z (*100) $ Vec3 1 2 3

-- | 2- and 3-Tuple instances for x and y.
instance HasX (Double, a) Double where
  x = _1

instance HasY (a, Double) Double where
  y = _2

instance HasX (Double, a, b) Double where
  x = _1

instance HasY (a, Double, b) Double where
  y = _2

instance HasZ (a, b, Double) Double where
  z = _3