#12423: Panic with DeriveAnyClass and DefaultSignatures -------------------------------------+------------------------------------- Reporter: knrafto | Owner: Type: bug | Status: new Priority: normal | Milestone: Component: Compiler | Version: 8.0.1 Keywords: | Operating System: Unknown/Multiple Architecture: | Type of failure: None/Unknown Unknown/Multiple | Test Case: | Blocked By: Blocking: | Related Tickets: Differential Rev(s): | Wiki Page: -------------------------------------+------------------------------------- With the code {{{#!hs {-# LANGUAGE DefaultSignatures, DeriveAnyClass #-} class Eq1 f where (==#) :: Eq a => f a -> f a -> Bool default (==#) :: Eq (f a) => f a -> f a -> Bool (==#) = (==) data Foo a = Foo (Either a a) deriving (Eq, Eq1) }}} GHC 8.0.1 and 7.10.3 both panic: {{{ ghc: panic! (the 'impossible' happened) (GHC version 8.0.1 for x86_64-apple-darwin): in other argument Please report this as a GHC bug: http://www.haskell.org/ghc/reportabug }}} -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/12423 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler