#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 simonpj): Here's what is happening * The given `b ~ f b` has an occurs check, so it's insoluble. It's a bit like saying {{{ f :: (Int ~ Bool) => blah }}} * In the long discussion on #12466 (see `Note [Given errors]` in `TcErrors` we decided not to complain about insoluble givens. * So the given `b ~ f b` is just parked. * Now we try to solve `b ~ f b`. Lo, it has an occurs-check error. Which we report. Seems reasonable to me, except for the lack of a complaint about the insoluble given; better ideas welcome (but look at #12466). -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/14323#comment:1 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler