#11324: Missing Kind Inference -------------------------------------+------------------------------------- Reporter: crockeea | Owner: Type: bug | Status: closed Priority: normal | Milestone: Component: Compiler | Version: 7.10.2 Resolution: invalid | 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: | -------------------------------------+------------------------------------- Changes (by rwbarton): * status: new => closed * resolution: => invalid Comment:
I think GHC should know the kind from the constraint on `foo`.
The kind of what? Since `CharOf` is polykinded in its result kind, there could be two different instances {{{ type instance CharOf T = True -- really "type instance CharOf Bool T = True" type instance CharOf T = () -- really "type instance CharOf * T = ()" }}} The occurrence of `CharOf fp` in `MyConstraint (CharOf fp)` must have kind `Bool`, because that is the kind that `MyConstraint` takes. But there is no reason why the subsequent occurrence of `CharOf fp` must have the same kind. This is illustrated by your two working examples. In the first one, `Bin` is not `Bool`! -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/11324#comment:1 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler