#14765: Levity polymorphism panic -------------------------------------+------------------------------------- Reporter: dfeuer | Owner: (none) Type: bug | Status: new Priority: normal | Milestone: 8.6.1 Component: Compiler | Version: 8.5 Keywords: | Operating System: Unknown/Multiple Architecture: | Type of failure: Compile-time Unknown/Multiple | crash or panic Test Case: | Blocked By: Blocking: | Related Tickets: Differential Rev(s): | Wiki Page: -------------------------------------+------------------------------------- I imagine I have made a mistake, but GHC shouldn't panic! {{{#!hs {-# language TypeInType, ScopedTypeVariables, MagicHash #-} import GHC.Exts (TYPE, Proxy#, proxy#) fold :: forall rep a (r :: TYPE rep). (r -> a -> Proxy# r -> r) -> (Proxy# r -> r) -> [a] -> r fold f k [] = k proxy# fold f k (x : xs) = fold f (f (k proxy#) x) xs }}} This gives me {{{ ghc-stage2: panic! (the 'impossible' happened) (GHC version 8.5.20171211 for x86_64-unknown-linux): splitFunTy () Call stack: CallStack (from HasCallStack): callStackDoc, called at compiler/utils/Outputable.hs:1150:37 in ghc:Outputable pprPanic, called at compiler/types/Type.hs:921:30 in ghc:Type }}} -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/14765 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler