main.hs

{-# LANGUAGE TemplateHaskell, DataKinds, TypeOperators, FlexibleContexts #-}
{-# OPTIONS_GHC -fno-warn-unticked-promoted-constructors #-}

import Data.Extensible
import Control.Lens hiding ((:>))

mkField "x y"
r = emptyRecord

foo = (x @= 1 <: y @= 2 <: r) == (y @= 2 <: x @= 1 <: r)

{-
  main.hs:10:45: error:
      • Couldn't match type ‘'Missing "x"’ with ‘'Expecting (n1 ':> v1)’
          arising from a use of ‘x’
      • In the first argument of ‘(@=)’, namely ‘x’
        In the first argument of ‘(<:)’, namely ‘x @= 1’
        In the second argument of ‘(<:)’, namely ‘x @= 1 <: r’
     |
  10 | foo = (x @= 1 <: y @= 2 <: r) == (y @= 2 <: x @= 1 <: r)
     |                                             ^
-}