#10532: Unnecessary constraints when using overlapping instances -------------------------------------+------------------------------------- Reporter: MikeIzbicki | Owner: Type: bug | 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 goldfire): This looks like expected behavior to me. In the overlapping instances case, GHC can't know which instance to choose when calling `foo` from `f`. If you want GHC to decide based on whether `a` is `Int` at a particular call site, then that's exactly what adding the constraint to `f`'s type signature means. -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/10532#comment:2 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler