#10978: Anonymous type instances -------------------------------------+------------------------------------- Reporter: benjamin.hodgson | Owner: Type: feature request | Status: new Priority: normal | Milestone: Component: Compiler (Type | Version: 7.8.3 checker) | Resolution: | Keywords: 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 goldfire): I don't see any structural problems with this proposal, but I think it doesn't pay its way. It would be yet another wrinkle to already-quite- complex type family story. And, I think more problematically, this approach would prohibit you to write class instances for these new datatypes. Because type families are not injective and generative, you cannot specify a type family in a class instance head. But with these "anonymous type instances", there would be no other way to name the datatype, so you've effectively made datatypes for which no instances can exist. (Except maybe by `deriving`. But you'd even be prohibited from standalone-deriving.) So I'm skeptical, even though I do think the underlying idea is sound. If you really want this, find a loud chorus of people who think likewise. :) -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/10978#comment:2 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler