#16315: Pattern synonym implicit existential quantification -------------------------------------+------------------------------------- Reporter: int-index | Owner: (none) Type: bug | Status: new Priority: normal | Milestone: Component: Compiler | Version: 8.6.3 Resolution: | Keywords: Operating System: Unknown/Multiple | Architecture: | Unknown/Multiple Type of failure: None/Unknown | Test Case: Blocked By: | Blocking: Related Tickets: | Differential Rev(s): Wiki Page: | -------------------------------------+------------------------------------- Comment (by RyanGlScott): OK. If I understand you correctly, then the original program with `k` uncommented should be accepted. (I think you were hinting at this all along, but it wasn't obvious to me until comment:7.) If that's the case, then it sounds like the proper course of action is to: * Proceed with https://gitlab.haskell.org/ghc/ghc/merge_requests/374, as it will get rid of the awkwardness brought about by implicitly quantified variables being brought into scope. * Moreover, !374 can revert most of #14998: * There is no longer any need for `PatSynExPE`, since implicitly quantified existentials are no longer brought into scope. * `Note [Pattern synonym existentials do not scope]` can go away. * The `T14498` test case can be removed. (Or, alternatively, we could explicitly quantify `k` and move it to `patsyn/should_compile`.) Does this sound right? -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/16315#comment:8 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler