#15707: More liberally kinded coercions for newtypes -------------------------------------+------------------------------------- Reporter: mniip | Owner: (none) Type: feature request | Status: new Priority: normal | Milestone: 8.6.1 Component: Compiler (Type | Version: 8.6.1 checker) | Resolution: | Keywords: Roles Operating System: Unknown/Multiple | Architecture: | Unknown/Multiple Type of failure: None/Unknown | Test Case: Blocked By: | Blocking: Related Tickets: #12369 | Differential Rev(s): Wiki Page: | -------------------------------------+------------------------------------- Comment (by mniip): Replying to [comment:2 goldfire]:
I see where you're getting, but it's still wishy-washy to me. Is there a concrete program you'd like to write with this feature?
Me (and partly ekmett) are experimenting with the idea of building a polykinded generics framework using a type-level combinatory calculus. So there's a handful of such data families involved, acting as combinators. In practice of course the family can't be infinite and we have to stop at some arity. We could unsafely introduce a coercion of the desired shape, but then what if someone extends the family? -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/15707#comment:4 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler