#15709: GHC panic using TypeInType with minimal source code -------------------------------------+------------------------------------- Reporter: jnape | Owner: (none) Type: bug | Status: new Priority: normal | Milestone: Component: Compiler | Version: 8.4.3 Keywords: TypeInType | Operating System: Linux Architecture: x86_64 | Type of failure: Compile-time (amd64) | crash or panic Test Case: | Blocked By: Blocking: | Related Tickets: Differential Rev(s): | Wiki Page: -------------------------------------+------------------------------------- The following source code causes GHC 8.4.3 on 64bit Linux to panic: {{{#!haskell {-# LANGUAGE TypeInType #-} module Lib where import Data.Kind class Contravariant f where contramap :: (a -> b) -> f b -> f a dimap :: (Contravariant (p :: * -> b -> p * b), Functor (p a)) => (z -> a) -> (b -> c) -> p a b -> p z c dimap f g = contramap f . fmap g }}} I have no idea if it should compile or not, but it shouldn't do this: {{{ ghc: panic! (the 'impossible' happened) (GHC version 8.4.3 for x86_64-unknown-linux): piResultTy k_a34u[tau:1] * Call stack: CallStack (from HasCallStack): callStackDoc, called at compiler/utils/Outputable.hs:1150:37 in ghc:Outputable pprPanic, called at compiler/types/Type.hs:947:35 in ghc:Type Please report this as a GHC bug: http://www.haskell.org/ghc/reportabug }}} -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/15709 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler