#16287: :kind accepts bogus type -------------------------------------+------------------------------------- Reporter: simonpj | Owner: (none) Type: bug | Status: new Priority: normal | Milestone: Component: Compiler | Version: 8.6.3 Resolution: | Keywords: Operating System: Unknown/Multiple | Architecture: | Unknown/Multiple Type of failure: None/Unknown | Test Case: Blocked By: | Blocking: Related Tickets: | Differential Rev(s): Wiki Page: | -------------------------------------+------------------------------------- Comment (by RyanGlScott): From a quick glance, I would guess that the only reason for `check_syn_tc_app` calling `check_type` instead of `check_arg_type` is due to `LiberalTypeSynonyms`. For instance, consider this (where `T` is a type synonym) {{{ λ> :set -XLiberalTypeSynonyms -XRankNTypes λ> type T a = a λ> :k T (forall a. a) }}} If you check `T`'s argument with `check_type` (as `check_syn_tc_app` does currently), then this will be accepted. If you check it with `check_arg_type`, however, it will be rejected: {{{ Illegal polymorphic type: forall a. a GHC doesn't yet support impredicative polymorphism }}} The difference amounts to whether you set `ve_rank` to `synArgMonoType` (as `check_syn_tc_app` does before invoking `check_type`) or `tyConArgMonoType` (as `check_arg_type` does). Perhaps we can tweak `check_arg_type` so that it knows when to use `synArgMonoType`—it might be as simple as passing an extra `Bool` argument to `check_arg_type` indicating whether this is the argument to a type synonym or not. -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/16287#comment:3 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler