#14880: GHC panic: updateRole -------------------------------------+------------------------------------- Reporter: RyanGlScott | Owner: goldfire Type: bug | Status: new Priority: normal | Milestone: 8.8.1 Component: Compiler (Type | Version: 8.2.2 checker) | Resolution: | Keywords: TypeInType Operating System: Unknown/Multiple | Architecture: Type of failure: Compile-time | Unknown/Multiple crash or panic | Test Case: Blocked By: | Blocking: Related Tickets: #15076 | Differential Rev(s): Phab:D4769, Wiki Page: | Phab:D5141 -------------------------------------+------------------------------------- Comment (by goldfire): * First off, no mists of time here: the more ambitious patch was because comment:13 fixed the problem in TcType -- which caused the original bug -- but that same problem existed in TyCoRep. We just didn't have (and still don't, to my knowledge) a concrete program that exhibits misbehavior. I don't remember the exact cause of the bug I mentioned in comment:13, but I don't think that's about the changes in TyCoRep. * Your new approach relies on this invariant: If a variable in a tyvar kind is in the bound-var set, then the variable is in the bound-var set, too. Perhaps easier is to think about the contrapositive: If a variable is not in the bound-var set (in other words, if we look at it at all), then no variable in its kind is in the bound-var set (so we can zap the bound- var set). This invariant is certainly true of well-typed programs. (It's just barely conceivable that it might not be true in the case of a mis- ordered telescope, but let's not worry about that now.) So: yes, I think that works nicely. Nice idea. It's very much worth a Note. @tdammers: Do you think you can push this new idea through? I can write the Note if need be. -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/14880#comment:124 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler