#10845: Incorrect behavior when let binding implicit CallStack object -------------------------------------+------------------------------------- Reporter: nitromaster101 | Owner: gridaphobe Type: bug | Status: new Priority: normal | Milestone: Component: Compiler | Version: 7.11 Resolution: | Keywords: Operating System: Unknown/Multiple | Architecture: | Unknown/Multiple Type of failure: None/Unknown | Test Case: Blocked By: | Blocking: Related Tickets: #10846 | Differential Rev(s): -------------------------------------+------------------------------------- Comment (by simonpj): Ah, yes, you are correct. (You can have a nested implication with skolems but no givens; that's important. Here there are no skolems either, and it'd take a little longer to explain why.) Rather than conditionally suppressing the no-given solver for `CallStack`, a better way is probably this. * Remove the auto-solve for `CallStack` (with no givens) altogether. * Instead, look at `TcSimplify.simplifyInfer`. It figures out what to quantify over. At top level (look at `rhs_tclvl`) we don't want to quantify over `CallStack` constraints; instead we want to discharge (solve) them. After getting the constraints back from `approximateWC`, we can simply solve any un-solved `CallStack` constraints. Does that help? I should have though of this first. -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/10845#comment:10 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler