#16146: Trivial partial type signature kills type inference in the presence of GADTs -------------------------------------+------------------------------------- Reporter: goldfire | 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 simonpj): How do you propose to do step 1 (check that `p` is a subtype of `t2`)? Suppose `p` is `forall a. _ -> a`, and `t2` is `Int -> Int`. Now when we instantiate `p` (to do the subtype check), what do we do about that `_`?? We could satisfy the subtype with `_` = `Int`, or `_` = `a`. The point is that we can't hope to instantiate a partial type signature, and we should not attempt to do so. That's why I suggest that we might just squeeze by if there is visibly no quantification to be done. So I don't think comment:5 will work. -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/16146#comment:6 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler