#12860: GeneralizedNewtypeDeriving + MultiParamTypeClasses sends typechecker into an infinite loop -------------------------------------+------------------------------------- Reporter: RyanGlScott | Owner: Type: bug | Status: new Priority: normal | Milestone: Component: Compiler (Type | Version: 8.0.1 checker) | Resolution: | Keywords: Operating System: Unknown/Multiple | Architecture: Type of failure: Compile-time | Unknown/Multiple performance bug | Test Case: Blocked By: | Blocking: Related Tickets: | Differential Rev(s): Wiki Page: | -------------------------------------+------------------------------------- Comment (by simonpj): Well my efforts thus far have at least succeeded in getting an error message very promptly {{{ T12860.hs:12:13: error: • Reduction stack overflow; size = 201 When simplifying the following type: C y (Foo x) Use -freduction-depth=0 to disable this check (any upper bound you could choose might fail unpredictably with minor updates to GHC, so disabling the check is recommended if you're sure that type checking should terminate) • When deriving the instance for (C y (Foo x)) }}} -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/12860#comment:6 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler