#14904: Compiler panic (piResultTy) -------------------------------------+------------------------------------- Reporter: kcsongor | Owner: (none) Type: bug | Status: new Priority: normal | Milestone: Component: Compiler | Version: 8.2.2 (Type checker) | Keywords: | Operating System: Unknown/Multiple Architecture: | Type of failure: None/Unknown Unknown/Multiple | Test Case: | Blocked By: Blocking: | Related Tickets: 14873 Differential Rev(s): | Wiki Page: -------------------------------------+------------------------------------- Type-checking the following type family {{{#!hs type family F (f :: forall a. g a) :: Type where F (f :: forall a. g a) = Int }}} panics with the message: {{{#!txt ghc: panic! (the 'impossible' happened) (GHC version 8.4.0.20180118 for x86_64-apple-darwin): piResultTy k_aVM[tau:1] a_aVF[sk: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:950:35 in ghc:Type }}} The panic happens with HEAD, 8.4 and 8.2. 8.0 rejects the program with an error message, but even it panics on the following version: {{{#!hs type family F f :: Type where F ((f :: forall a. g a) :: forall a. g a) = Int }}} #14873 seemed somewhat related, so I tried with the patch implemented in 3d252037234ce48f9bdada7d5c9b1d8eba470829, but that fails with the same panic too. -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/14904 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler