gistfile1.txt

module Main where

import Data.NaturalTransformation (type (~>))
import Data.Symbol (class IsSymbol, SProxy)
import Prim.Row as Row
import Unsafe.Coerce (unsafeCoerce)

data VariantRF (s :: # Type) (r :: # Type) (a :: Type)

data RFProxy (f :: # Type -> Type -> Type) = RFProxy

newtype MuVariantRF r a = InVariantRF (VariantRF r r a)

inj :: forall u sym s r f
  .   Row.Cons sym (RFProxy f) u r
  =>  IsSymbol sym
  =>  SProxy sym
  ->  f s
  ~>  VariantRF s r
inj = unsafeCoerce 0
--

on :: forall u sym f s r a b
  .   Row.Cons sym (RFProxy f) u r
  =>  IsSymbol sym
  =>  SProxy sym
  ->  (f s a -> b)
  ->  (VariantRF s u a -> b)
  ->  VariantRF s r a
  ->  b
on = unsafeCoerce 0