"While were in there", it occurred to me that one `coerce` per constructor argument ideally ought to suffice. On Mon, Aug 15, 2016, 07:17 GHC wrote:

#8516: Add (->) representation and the Invariant class to GHC.Generics -------------------------------------+------------------------------------- Reporter: nfrisby | Owner: Type: feature request | Status: new Priority: low | Milestone: Component: Compiler (Type | Version: 7.7 checker) | Resolution: | Keywords: Generics 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 RyanGlScott):

And as it turns out, goldfire has a separate ticket (#8177) for the proposed idea of being able to give explicit role signatures to type families, which might make the potential regression in [https://ghc.haskell.org/trac/ghc/ticket/8516#comment:7 this comment] not an actual regression. See my comment [https://ghc.haskell.org/trac/ghc/ticket/8177#comment:31 here].

-- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/8516#comment:11 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler