#9220: type roles for unboxed arrays -------------------------------------+------------------------------------- Reporter: rwbarton | Owner: goldfire Type: bug | Status: new Priority: normal | Milestone: 7.10.1 Component: Core | Version: 7.8.1 Libraries | Keywords: Resolution: | Architecture: Unknown/Multiple Operating System: | Difficulty: Unknown Unknown/Multiple | Blocked By: Type of failure: | Related Tickets: None/Unknown | Test Case: | Blocking: | Differential Revisions: | -------------------------------------+------------------------------------- Comment (by ekmett): Boxed arrays are representational (just by the default roles) though both `Array` and `UArray` are currently ''also'' `representational` in the first argument. =/ That is dangerous for much the same reason as relying on the semantics of `Storable` not changing to a newtype, it is often the very point that the newtype would change such an instance. In fact `UArray` is currently even worse and gets inferred as {{{ type role UArray representational phantom -- ack! }}} because the underlying constructor doesn't mention the element type at all. We basically just ignored roles in the `array` package when shipping 7.8.x -- It strikes me that we should have {{{ type role Array nominal representational type role UArray nominal nominal }}} The first argument is formed nominal by depending upon the chosen `Ix` instance, and in the case of `UArray` the second argument is forced nominal by depending upon the chosen `Storable` instance. -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/9220#comment:24 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler