#10343: Make Typeable track kind information better -------------------------------------+------------------------------------- Reporter: oerjan | Owner: goldfire Type: feature request | Status: new Priority: normal | Milestone: 7.12.1 Component: Compiler | Version: 7.10.1 Resolution: | Keywords: Operating System: Unknown/Multiple | Architecture: Type of failure: None/Unknown | Unknown/Multiple Blocked By: | Test Case: typeOf :: Related Tickets: #9858 | Typeable (a::k) => Proxy a -> | TypeRep | Blocking: | Differential Revisions: -------------------------------------+------------------------------------- Changes (by goldfire): * owner: => goldfire * milestone: => 7.12.1 Comment: This all continues to seem straightforward to me, but I maintain (in contrast to Simon's claim in comment:8) that this is separate from kind equalities. My implementation approach would be, as oerjan suggests, adding a `kindRep` field in `TypeRep`. This can be done today. Then, define {{{ class Typeable k => Typeable (a :: k) where ... -- probably not possible until I merge }}} This appears to be a superclass cycle, but we know it doesn't induce infinite regress because the kind of a kind is always `*`. So, we arrange to have this definition accepted. Then, the solver will just do the right thing. When we have a given `Typeable (a :: k)` constraint, the solver will spit off a `Typeable (k :: *)` constraint. We may have to arrange for the solver not to then spit off a (harmless, but potentially confusing) `Typeable (* :: *)` constraint. To work with `typeOf :: Typeable a => Proxy a -> TypeRep`... well it will all just work. Typechecking this expression leads to {{{ [G] Typeable (a :: k) [W] Typeable (Proxy (a :: k)) }}} After a little work, the solver arrives at {{{ [G] Typeable (a :: k) [G] Typeable (k :: *) [W] Typeable (Proxy :: k -> *) -- the Typeable solver doesn't decompose kind applications [W] Typeable (a :: k) }}} The wanteds are easily solved from the givens. Since I'm the one with the plan, sounds like I should be the one to execute the plan. But probably only after I merge, since this isn't something we need today. -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/10343#comment:12 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler