#14419: Check kinds for ambiguity -------------------------------------+------------------------------------- Reporter: goldfire | Owner: (none) Type: bug | Status: new Priority: normal | Milestone: Component: Compiler | Version: 8.2.1 Resolution: | Keywords: TypeInType Operating System: Unknown/Multiple | Architecture: | Unknown/Multiple Type of failure: None/Unknown | Test Case: Blocked By: | Blocking: Related Tickets: | Differential Rev(s): Wiki Page: | -------------------------------------+------------------------------------- Description changed by goldfire: Old description:
GHC does an ambiguity check on types. It should also do the same for kinds. Here is a program that should be rejected:
{{{#!hs type family F a data T :: F a -> Type }}}
`T`'s kind is ambiguous, and any occurrence of `T` will be rejected. Instead of rejecting usage sites, let's just reject the definition site.
This check would be disabled by `AllowAmbiguousTypes`.
Happily, I think the implementation should be easy, and that the current algorithm to check for ambiguous types should work for kinds, too. After all, types and kinds are the same these days.
This was inspired by #14203, but no need to read that ticket to understand this one.
New description: GHC does an ambiguity check on types. It should also do the same for kinds. Here is a program that should be rejected: {{{#!hs type family F a data T :: F a -> Type }}} `T`'s kind is ambiguous, and any occurrence of `T` will be rejected. Instead of rejecting usage sites, let's just reject the definition site. This check would be disabled by `AllowAmbiguousTypes`. Happily, I think the implementation should be easy, and that the current algorithm to check for ambiguous types should work for kinds, too. After all, types and kinds are the same these days. This was inspired by #14203, but no need to read that ticket to understand this one. EDIT: See comment:8 and comment:10 for the nub of what needs to be done here. -- -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/14419#comment:11 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler