#12680: Permit type equality instances in signatures -------------------------------------+------------------------------------- Reporter: ezyang | Owner: Type: feature request | Status: new Priority: low | Milestone: Component: Compiler (Type | Version: 8.1 checker) | Resolution: | Keywords: backpack Operating System: Unknown/Multiple | Architecture: | Unknown/Multiple Type of failure: None/Unknown | Test Case: Blocked By: | Blocking: Related Tickets: | Differential Rev(s): Wiki Page: | -------------------------------------+------------------------------------- Comment (by ezyang):
Fix what? I like the current behavior of the hs-boot file, because all data-types really are injective. Or do you mean fix what's used in a signature?
What we use in an hsig file. I guess, type synonyms should not be allowed to implement abstract data; and then add a new type construct which doesn't assume injectivity.
The Nat one (comment:3) is a great starting point.
So, assuming that you had this equality floating around, would it actually do something useful? -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/12680#comment:8 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler