Re: [GHC] #10592: Allow cycles in class declarations

#10592: Allow cycles in class declarations -------------------------------------+------------------------------------- Reporter: MikeIzbicki | Owner: Type: feature request | Status: infoneeded Priority: normal | Milestone: Component: Compiler (Type | Version: 7.10.1 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 Simon Peyton Jones ): In [changeset:"ff752a1a5eb69955c0e4fda8647f495409a2c384/ghc" ff752a1a/ghc]: {{{ #!CommitTicketReference repository="ghc" revision="ff752a1a5eb69955c0e4fda8647f495409a2c384" tcCheckSatisfiability: less aggressive superclass expansion In the pattern-match check we are looking for a proof of *unsatisfiablity* among a bunch of givens. The unsat-ness might be hidden in the superclasses, so we must expand them. But in the common case where the constraints are satisfiable, we don't want to expand a recursive superclass forever. This is all a bit arbitrary, but then the whole question is undecidable anyway. The bug in Trac #10592 comment:12 was that I expanded superclasses forever. This patch fixes it. }}} -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/10592#comment:15 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler