#14131: Difference between newtype and newtype instance -------------------------------------+------------------------------------- Reporter: Iceland_jack | Owner: (none) Type: bug | Status: patch Priority: normal | Milestone: Component: Compiler | Version: 8.2.1 Resolution: | Keywords: TypeFamilies Operating System: Unknown/Multiple | Architecture: | Unknown/Multiple Type of failure: None/Unknown | Test Case: Blocked By: | Blocking: Related Tickets: #7938, #9574, | Differential Rev(s): Phab:D3872 #13985 | Wiki Page: | -------------------------------------+------------------------------------- Changes (by RyanGlScott): * related: #13985 => #7938, #9574, #13985 Comment: It's also worth noting that Phab:D3872 reverses a design decision made in #7938 and #9574 to only allow kind variables in the RHSes of associated type instances if they're explicitly bound by LHS type patterns. But I think this is the right thing to do, because otherwise you can't have things like: {{{#!hs class C k where data family Nat :: k -> k -> Type instance C (k -> Type) where newtype Nat :: (k -> Type) -> (k -> Type) -> Type where Nat :: (forall xx. f xx -> g xx) -> Nat f g }}} And rejecting this feels like the wrong stance to take. -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/14131#comment:7 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler