#11681: ghc panic with TypeError -------------------------------------+------------------------------------- Reporter: inaki | Owner: Type: bug | Status: new Priority: normal | Milestone: 8.0.1 Component: Compiler (Type | Version: 8.0.1-rc2 checker) | Resolution: | Keywords: Operating System: Unknown/Multiple | Architecture: Type of failure: Compile-time | Unknown/Multiple crash | Test Case: Blocked By: | Blocking: Related Tickets: | Differential Rev(s): Wiki Page: | -------------------------------------+------------------------------------- Comment (by aavogt): I can't reproduce the original problem with -rc2 either, but I get the original error message with this file: {{{#!hs {-# LANGUAGE FlexibleInstances #-} class C x where m :: x () class B x instance B x => C x }}} {{{ ghc: panic! (the 'impossible' happened) (GHC version 8.0.0.20160204 for x86_64-unknown-linux): fvProv falls into a hole {a1eE} }}} Interestingly the kind error is in there if we're missing FlexibleInstances {{{ kind_error_fvprov.hs:12:17: error: ? Illegal instance declaration for ?C x? (All instance types must be of the form (T a1 ... an) where a1 ... an are *distinct type variables*, and each type variable appears at most once in the instance head. Use FlexibleInstances if you want to disable this.) ? In the instance declaration for ?C x? kind_error_fvprov.hs:12:19: error: ? Expected kind ?* -> *?, but ?x? has kind ?*? ? In the first argument of ?C?, namely ?x? In the instance declaration for ?C x? }}} -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/11681#comment:5 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler