#10114: Kind mismatches with AnyK in rank-2 types -------------------------------------+------------------------------------- Reporter: cam | Owner: Type: bug | Status: new Priority: normal | Milestone: Component: Compiler | Version: 7.8.4 Resolution: | Keywords: Operating System: Unknown/Multiple | Architecture: Type of failure: GHC rejects | Unknown/Multiple valid program | Test Case: Blocked By: | Blocking: Related Tickets: | Differential Revisions: -------------------------------------+------------------------------------- Comment (by simonpj): It's amazing how easily I can be confused by this stuff! To the question of why restricting foralls to have result of kind `*`, maybe I can attempt to answer my own question, thus: in what context could you could use such a type? Obviously not in a type signature, since that must have kind `*`. Where else? Would it make sense to say `T (forall a. Either a)`? But if `T` expected an arg of kind `* -> *`, does it make sense to instantiate it with `(forall a. Either a)`? Does the type `(forall a. Either a) Int` make sense? Maybe not. Re unboxed tuples, maybe you are right. Perhaps it only matters in very special cases like `forall a. (# a, a #)` which may not be very important. In short, maybe we should explore * `forall` always has kind `*` * Kind-generalise the RHS of type synonyms, so we get the kind in comment:4 -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/10114#comment:7 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler