{-# LANGUAGE TemplateHaskell #-}

import Data.Foldable
import Language.Haskell.TH

data Point = Point { x :: Double
                   , y :: Double
                   }
  deriving Show

let
  zipFields :: Q Exp -> Q Exp -> [Q Exp] -> Q Exp
  zipFields ctor op fields =
    foldl' (\prefix field -> [|$prefix ($op ($field a) ($field b))|]) ctor fields
  in [d|
    addPoint :: Point -> Point -> Point
    addPoint a b = $(zipFields [|Point|] [|(+)|] [[|x|], [|y|]])
  |]

main :: IO ()
main = print $ addPoint (Point 1.0 2.0) (Point 0.3 0.4)