#7854: Constrained method type accepted in Haskell 98 mode -------------------------------------+------------------------------------- Reporter: refold | Owner: thomie Type: bug | Status: patch Priority: normal | Milestone: 7.12.1 Component: Compiler (Type | Version: 7.6.3 checker) | Keywords: newcomer Resolution: | Architecture: Operating System: Unknown/Multiple | Unknown/Multiple Type of failure: None/Unknown | Test Case: Blocked By: | typechecker/should_fail/T7854 Related Tickets: #10118, #10119 | Blocking: | Differential Revisions: Phab:D688 -------------------------------------+------------------------------------- Comment (by Simon Peyton Jones <simonpj@…>): In [changeset:"f66e0e695b0377c469fbe877d4850fc0ebca2010/ghc"]: {{{ #!CommitTicketReference repository="ghc" revision="f66e0e695b0377c469fbe877d4850fc0ebca2010" A raft of small changes associated with -XConstrainedClassMethods See Trac #7854. Specifically: * Major clean up and simplification of check_op in checkValidClass; specifically - use checkValidType on the entire method-selector type to detect ambiguity - put a specific test for -XConstrainedClassMethods * Make -XConstrainedClassMethods be implied by -XMultiParamTypeClasses (a bit ad-hoc but see #7854), and document in the user manual. * Do the checkAmbiguity test just once in TcValidity.checkValidType, rather than repeatedly at every level. See Note [When to call checkAmbiguity] * Add -XAllowAmbiguousTypes in GHC.IP, since 'ip' really is ambiguous. (It's a rather magic function.) * Improve location info for check_op in checkValidClass * Update quite a few tests, which had genuinely-ambiguous class method signatures. Some I fixed by making them unambiguous; some by adding -XAllowAmbiguousTypes }}} -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/7854#comment:12> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler