Re: [GHC] #9033: Type error suppresses defaulting, causes spurious errors

#9033: Type error suppresses defaulting, causes spurious errors ---------------------------------+----------------------------------------- Reporter: jun0 | Owner: Type: bug | Status: new Priority: normal | Milestone: Component: Compiler | Version: 7.8.2 Resolution: | Keywords: defaulting, ambiguous Operating System: | Architecture: Unknown/Multiple Unknown/Multiple | Difficulty: Unknown Type of failure: None/Unknown | Blocked By: Test Case: | Related Tickets: Blocking: | ---------------------------------+----------------------------------------- Comment (by Simon Peyton Jones ): In [changeset:"ba2e20149e2addaccf5ce3122d3a6e93da696a0a/ghc"]: {{{ #!CommitTicketReference repository="ghc" revision="ba2e20149e2addaccf5ce3122d3a6e93da696a0a" Do type-class defaulting even if there are insoluble constraints The argument in Trac #9033 is very compelling: we should not report 20 errors, fix one, and have the other 19 disappear. They were spurious in the first place. The fix was easy; do type-class defaulting uncondionally, rather than only if there are no insoluble constraints. See Note [When to do type-class defaulting] in TcSimplify. Error messages generally improve, especially tc211 which actually had an example of precisely this phenomenon. }}} -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/9033#comment:1 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler