Re: [GHC] #15552: Infinite loop/panic with an existential type.

#15552: Infinite loop/panic with an existential type. -------------------------------------+------------------------------------- Reporter: howtonotwin | Owner: (none) Type: bug | Status: new Priority: normal | Milestone: 8.6.1 Component: Compiler | Version: 8.4.3 Resolution: | Keywords: TypeInType, | TypeFamilies Operating System: Unknown/Multiple | Architecture: Type of failure: Compile-time | Unknown/Multiple crash or panic | Test Case: Blocked By: | Blocking: Related Tickets: #14723 | Differential Rev(s): Wiki Page: | -------------------------------------+------------------------------------- Comment (by Simon Peyton Jones ): In [changeset:"565ef4cc036905f9f9801c1e775236bb007b026c/ghc" 565ef4c/ghc]: {{{ #!CommitTicketReference repository="ghc" revision="565ef4cc036905f9f9801c1e775236bb007b026c" Remove knot-tying bug in TcHsSyn.zonkTyVarOcc There was a subtle knot-tying bug in TcHsSyn.zonkTyVarOcc, revealed in Trac #15552. I fixed it by * Eliminating the short-circuiting optimisation in zonkTyVarOcc, instead adding a finite map to get sharing of zonked unification variables. See Note [Sharing when zonking to Type] in TcHsSyn * On the way I /added/ the short-circuiting optimisation to TcMType.zonkTcTyVar, which has no such problem. This turned out (based on non-systematic measurements) to be a modest win. See Note [Sharing in zonking] in TcMType On the way I renamed some of the functions in TcHsSyn: * Ones ending in "X" (like zonkTcTypeToTypeX) take a ZonkEnv * Ones that do not end in "x" (like zonkTcTypeToType), don't. Instead they whiz up an empty ZonkEnv. }}} -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/15552#comment:10 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler