#14110: GHC Panic on over-saturated associated type family -------------------------------------+------------------------------------- Reporter: Iceland_jack | Owner: (none) Type: bug | Status: new Priority: normal | Milestone: Component: Compiler | Version: 8.2.1 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: -------------------------------------+------------------------------------- If we over-saturate a type family {{{#!hs {-# Language TypeFamilies, ScopedTypeVariables, PolyKinds, DataKinds #-} import Data.Kind class R (c :: k -> Constraint) where type R_ (c :: k -> Constraint) :: k -> Type instance R Eq where type R_ Eq a = a -> a -> Bool }}} we get {{{ $ ghci -ignore-dot-ghci test.hs GHCi, version 8.3.20170605: http://www.haskell.org/ghc/ :? for help [1 of 1] Compiling Main ( test.hs, interpreted ) ghc: panic! (the 'impossible' happened) (GHC version 8.3.20170605 for x86_64-unknown-linux): repSplitAppTys a_a2qu[sk:1] a_a2qu[sk:1] -> Bool [] Call stack: CallStack (from HasCallStack): prettyCurrentCallStack, called at compiler/utils/Outputable.hs:1133:58 in ghc:Outputable callStackDoc, called at compiler/utils/Outputable.hs:1137:37 in ghc:Outputable pprPanic, called at compiler/types/Type.hs:809:9 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/14110 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler