Typeclass dictionary equality test

typeclass_method_equality.hs

{-# language BangPatterns #-}
{-# language UnboxedTuples #-}
{-# language TypeInType #-}
{-# language GeneralizedNewtypeDeriving #-}
{-# language TypeApplications #-}
{-# language MagicHash #-}

import Data.Primitive
import GHC.Exts
import Data.Int

main :: IO ()
main = do
  putStrLn "Beginning"
  let !x = (readByteArray# @Foo)
  let !y = (unsafeCoerce# (readByteArray# @Bar))
  case reallyUnsafePtrEquality# x y of
    1# -> putStrLn "Equal"
    _ -> putStrLn "Not Equal"
  putStrLn "Finished"

newtype Foo = Foo Int8
  deriving (Prim)

newtype Bar = Bar Int8
  deriving (Prim)