#14323: Occurs check regressions in GHC 8.2.1 (and HEAD) -------------------------------------+------------------------------------- Reporter: RyanGlScott | Owner: (none) Type: bug | Status: new Priority: normal | Milestone: Component: Compiler (Type | Version: 8.2.1 checker) | 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): I'm quite confused. Why should an occurs check ever fire in the first place for `b ~R# f b`? This is a perfectly legitimate constraint that can be witnessed, for instance, by letting `f` be `Identity` (since `b` is representationally equal to `Identity b`). Thus, I'd argue that `hm2` and `hm3` are //not// wrong programs. -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/14323#comment:4 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler