#12928: Too easy to trigger CUSK condition using TH -------------------------------------+------------------------------------- Reporter: int-index | Owner: Type: feature request | Status: new Priority: high | Milestone: Component: Compiler (Type | Version: 8.0.1 checker) | Resolution: | Keywords: Operating System: Unknown/Multiple | Architecture: Type of failure: GHC rejects | Unknown/Multiple valid program | Test Case: Blocked By: | Blocking: Related Tickets: | Differential Rev(s): Wiki Page: | -------------------------------------+------------------------------------- Comment (by goldfire): Another way to see the difference is that GHC uses the definition of a type to inform its kinds. That is, {{{ data T a = MkT (a Int) }}} will infer `a :: Type -> Type`. On the other hand, term-level type signatures stand entirely on their own, as Simon says. So, {{{ x :: forall a. Proxy a x = Proxy :: Proxy (a :: Type) }}} is rejected, even though choosing `a :: Type` in the type signature would work here. I've been favoring having standalone type-level kind signatures for some time, and am waiting for the right time to introduce a ghc-proposal to this end. CUSKs are terribly fiddly and very unexpected to users! -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/12928#comment:9 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler