#14331: Overzealous free-floating kind check causes deriving clause to be rejected -------------------------------------+------------------------------------- Reporter: RyanGlScott | Owner: (none) Type: bug | Status: merge Priority: normal | Milestone: 8.2.2 Component: Compiler (Type | Version: 8.2.1 checker) | Resolution: | Keywords: deriving Operating System: Unknown/Multiple | Architecture: | Unknown/Multiple Type of failure: GHC rejects | Test Case: valid program | deriving/should_compile/T14331 Blocked By: | Blocking: Related Tickets: | Differential Rev(s): Wiki Page: | -------------------------------------+------------------------------------- Comment (by simonpj): I agree. After elaboration we expect {{{ class C {k1 k2} (p::k1) (q::k2) data D {k3} (r::k3) = D instance forall {k2} k (a:k) (b:k2). C a (D {k2} b) where ... }}} So we instantiate the `k3` belonging to the data declaration to `k2` belonging to the instance. The `forall k` in the `deriving` clause is just the kind on `a`, the first parameter for `C`. Right? Why this doesn't work I don't know. -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/14331#comment:13 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler