#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 int-index): Here's a complete GHCi session to demonstrate the asymmetry: {{{ GHCi, version 8.0.1: http://www.haskell.org/ghc/ :? for help Prelude> :set -XTypeInType -XScopedTypeVariables Prelude> import Data.Proxy Prelude Data.Proxy> import Data.Kind Prelude Data.Proxy Data.Kind> data TyFun :: * -> * -> * Prelude Data.Proxy Data.Kind> fffSym0 (x :: TyFun (Proxy a) ()) = undefined :: Type Prelude Data.Proxy Data.Kind> :type fffSym0 fffSym0 :: forall k (a :: k). TyFun (Proxy a) () -> Type Prelude Data.Proxy Data.Kind> data FffSym0 (x :: TyFun (Proxy a) ()) :: Type <interactive>:7:1: error: You have written a *complete user-suppled kind signature*, but the following variable is undetermined: k0 :: * Perhaps add a kind signature. Inferred kinds of user-written variables: a :: k0 x :: TyFun (Proxy a) () }}} -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/12928#comment:8 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler