#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):
type S is much better, because users can't make any assumptions about a type declaration that they might for a data declaration.
As far as I could tell, GHC actually doesn't make any assumptions when `data S` denotes an abstract type; so it's just a syntactic wart. It's a bit bothersome to fix because hs-boot syntax only supports data.
It would be super awesome if the user could prove the equality manually.
Do you have an example of a case where you could do this? -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/12680#comment:4 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler