testsuite/tests/indexed-types/should_fail/T9554.hs


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{-# LANGUAGE TypeFamilies, UndecidableInstances #-}

module T9554 where

import Data.Proxy

type family F a where
  F a = F (F a)

foo :: Proxy (F Bool) -> Proxy (F Int)
foo x = x

main = case foo Proxy of Proxy -> putStrLn "Made it!"