#12088: Type/data family instances in kind checking -------------------------------------+------------------------------------- Reporter: alexvieth | Owner: Type: bug | Status: new Priority: high | Milestone: 8.2.1 Component: Compiler (Type | Version: 8.1 checker) | Resolution: | Keywords: TypeInType Operating System: Unknown/Multiple | Architecture: Type of failure: GHC rejects | Unknown/Multiple valid program | Test Case: Blocked By: | Blocking: Related Tickets: #11348, #12239 | Differential Rev(s): Phab:D2272 Wiki Page: | -------------------------------------+------------------------------------- Comment (by simonpj): Here's another example of the phasing problem, this one posted by [https://mail.haskell.org/pipermail/glasgow-haskell- users/2016-September/026399.html Dave Menendez]: {{{ {-# LANGUAGE TemplateHaskell, TypeInType, TypeFamilies #-} module DH where import Data.Kind (Type) type family K t :: Type type family T t :: K t -> Type data List type instance K List = Type type instance T List = [] -- Error on this line -- Error is: -- * Expected kind K List -> Type, but [] has kind `* -> *` -- In the type `[]` -- In the type instance declaration for `T` }}} The reasson is the we need teh `K List` instance to typecheck the `T List` instance. Adding a separator just before the `instance T List` declaration makes it work -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/12088#comment:30 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler