#10122: PolyKinds: inferred type not as polymorphic as possible -------------------------------------+------------------------------------- Reporter: thomie | Owner: Type: bug | Status: closed Priority: normal | Milestone: Component: Compiler | Version: 7.10.1-rc2 Resolution: invalid | Keywords: Operating System: Unknown/Multiple | Architecture: Type of failure: None/Unknown | Unknown/Multiple Blocked By: | Test Case: Related Tickets: | Blocking: | Differential Revisions: -------------------------------------+------------------------------------- Changes (by thomie): * status: new => closed * resolution: => invalid Comment: Thanks, you're right. I indeed did not set `-XPolyKinds` in GHCi, and didn't fully appreciate the difference between the types of `f1` and `f2`: {{{ f1 :: (forall (a::k) (m::k->*). m a -> Int) -> Int f2 :: (forall (k::BOX) (a::k) (m::k->*). m a -> Int) -> Int }}} I asked a stackoverflow [http://stackoverflow.com/questions/28772695 /rankntypes-and-polykinds question] about this, so that the answer will be easier to find. Possible documentation improvements: * an explanation or link to an explanation for `BOX` is missing (see 'Datatype promotion'). * the documentation shows the initial `forall (k:BOX)` in `f1`'s type, but GHCi and GHC error message leave it out. This could be made more clear. * the inferred type signatures show `:` instead of `::`, unnecessarily. * maybe add one more sentence about the implications the placement of the `kind forall`. -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/10122#comment:2 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler