#9357: Kind-polymorphic type family accepts unlifted type arguments -------------------------------------+------------------------------------- Reporter: kosmikus | Owner: Type: bug | Status: new Priority: normal | Milestone: Component: Compiler (Type | Version: 7.8.2 checker) | Operating System: Keywords: | Unknown/Multiple Architecture: Unknown/Multiple | Type of failure: GHC Difficulty: Unknown | accepts invalid program Blocked By: | Test Case: Related Tickets: | Blocking: | Differential Revisions: -------------------------------------+------------------------------------- The following code is accepted by ghc-7.8.2 and ghc-7.6.3: {{{#!hs {-# LANGUAGE TypeFamilies, MagicHash, PolyKinds #-} import GHC.Exts type family F (a :: k) :: * type instance F Int# = () }}} In nearly all other places, it seems that unlifted types are explicitly forbidden. I'm also not allowed to actually apply `F` to `Int#` after defining the type family like this. So I think the compiler should probably reject the `type instance`. (BTW, is it actually clear that using `#` as an argument kind to a type family or as an index kind for a GADT is in any way harmful?) -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/9357 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler