#10592: Allow cycles in class declarations -------------------------------------+------------------------------------- Reporter: MikeIzbicki | Owner: Type: feature request | Status: new Priority: normal | Milestone: Component: Compiler (Type | Version: 7.10.1 checker) | Keywords: Resolution: | Architecture: Operating System: Unknown/Multiple | Unknown/Multiple Type of failure: None/Unknown | Test Case: Blocked By: | Blocking: Related Tickets: | Differential Revisions: -------------------------------------+------------------------------------- Comment (by simonpj): The stuff in #10318 is speculation about a possible feature. But the question remains: in your application If {{{ class (Scalar (Scalar a) ~ Scalar a, Field (Scalar a)) => Vector a class Vector x => Field x }}} was accepted by GHC, would it serve your purpose? That means that in any instance of `Vector t`, GHC will need to prove that `Scalar (Scalar t) ~ Scalar t`. Will that be true, in your application? If so, that makes the speculation in #10318 more persuasive. -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/10592#comment:6 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler