#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 rwbarton): Well before 8.0, it results in a context reduction stack overflow reasonably quickly. The code is extremely dubious anyways, since the derived instance would have form {{{#!hs instance C b a => C b (Foo a) where ... }}} But if you could actually satisfy the context `C b a`, then you would be disallowed from writing the instance `C b (Foo a)` by the functional dependency. So the derived instance should be useless. -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/12860#comment:1 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler