#9201: GHC unexpectedly refines explicit kind signatures -------------------------------------+------------------------------------- Reporter: ekmett | Owner: Type: bug | Status: new Priority: normal | Milestone: Component: Compiler (Type | Version: 7.8.2 checker) | Operating System: Unknown/Multiple Keywords: | Type of failure: GHC accepts Architecture: Unknown/Multiple | invalid program Difficulty: Unknown | Test Case: Blocked By: | Blocking: Related Tickets: | -------------------------------------+------------------------------------- The following program should be rejected by the type checker: {{{ {-# LANGUAGE PolyKinds, FunctionalDependencies, MultiParamTypeClasses #-} class MonoidalCCC (f :: x -> y) (d :: y -> y -> *) | f -> d where ret :: d a (f a) }}} Instead it is accepted, but the kind variables specified above are 'corrected' during typechecking to: {{{
:browse class MonoidalCCC (f :: x -> x) (d :: x -> x -> *) | f -> d where ret :: d a (f a) }}}
This may be similar in root cause to issue #9200, but there a valid program is rejected, and here an invalid program is accepted, so the fixes may be quite different. It seems these kind variables are just being allowed to unify rather than being checked for subsumption. -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/9201 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler