SYB Test

Test.hs

{-# LANGUAGE RankNTypes #-}
module Test where

import Data.Generics
import Data.Void (Void)

myGeq :: forall a. Data a => a -> a -> Bool
myGeq a b = myGeq' a b
  where
    myGeq' :: GenericQ (GenericQ Bool)
    myGeq' x y
      | typeOf x == typeOf y,
        toConstr x == toConstr y
        = and $ gzipWithQ (
          myGeq'
          `extQ` impossible
        ) x y
      | otherwise = False
    
impossible :: Void -> GenericQ Bool
impossible _ _ = undefined