#15142: GHC HEAD regression: tcTyVarDetails -------------------------------------+------------------------------------- Reporter: RyanGlScott | Owner: (none) Type: bug | Status: new Priority: highest | Milestone: 8.6.1 Component: Compiler (Type | Version: 8.5 checker) | Keywords: TypeInType, Resolution: | TypeFamilies 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: | -------------------------------------+------------------------------------- Comment (by RyanGlScott): Some more observations about this: * If you swap out `TypeInType` for just `DataKinds` and `PolyKinds`, then the program no longer panics, so `TypeInType` appears to be critical in triggering this panic. * If you try and give the parameter to `ListToTuple` an explicit kind signature: {{{#!hs {-# LANGUAGE MultiParamTypeClasses #-} {-# LANGUAGE TypeFamilies #-} {-# LANGUAGE TypeInType #-} module Bug where import Data.Kind class ListTuple (tuple :: Type) (as :: [(k, Type)]) where type ListToTuple (as :: [(k, Type)]) :: Type }}} Then this will typecheck on GHC 8.4.2, but on HEAD it will give an error message: {{{ $ ~/Software/ghc/inplace/bin/ghc-stage2 Bug.hs [1 of 1] Compiling Bug ( Bug.hs, Bug.o ) Bug.hs:9:29: error: • Expected a type, but ‘k’ has kind ‘k0’ • In the kind ‘[(k, Type)]’ | 9 | type ListToTuple (as :: [(k, Type)]) :: Type | ^ }}} -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/15142#comment:2 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler