[GHC] #10343: Make Typeable track kind information better

[GHC]

#10343: Make Typeable track kind information better
-------------------------------------+-------------------------------------
        Reporter:  oerjan            |                Owner:  goldfire
            Type:  feature request   |               Status:  new
        Priority:  normal            |            Milestone:  8.0.1
       Component:  Compiler          |              Version:  7.10.1
      Resolution:                    |             Keywords:
Operating System:  Unknown/Multiple  |         Architecture:
                                     |  Unknown/Multiple
 Type of failure:  None/Unknown      |            Test Case:  typeOf ::
                                     |  Typeable (a::k) => Proxy a ->
                                     |  TypeRep
      Blocked By:                    |             Blocking:
 Related Tickets:  #9858             |  Differential Rev(s):
       Wiki Page:                    |
-------------------------------------+-------------------------------------

Comment (by bgamari):

 My goal was to augment the existing `Typeable` interface with a means of
 extracting the kind of the type represented by a given `TypeRep`. That is,
 {{{#!hs
 -- The current (non-type-indexed) TypeRep machinery
 data TypeRep
 type KindRep = TypeRep
 typeRep :: Typeable a => Proxy a -> TypeRep

 -- I wanted this...
 typeRepKind :: TypeRep -> KindRep
 }}}

 As far as I can tell, the semantics of `typeRepKind` should be clear so
 long as we are only talking about monomorphically kinded types. For
 instance,
 {{{#!hs
 kindRep :: Typeable a => Proxy a -> KindRep
 kindRep = typeRepKind . typeRep

 kindRep (Proxy :: Proxy Int)          == *
 kindRep (Proxy :: Proxy Int#)         == TYPE 'Unlifted
 kindRep (Proxy :: Proxy '[4])         == '[Nat]
 kindRep (Proxy :: Proxy (4 ':))       == '[Nat] -> '[Nat]
 kindRep (Proxy :: Proxy [])           == * -> *
 kindRep (Proxy :: Proxy [Int])        == *
 kindRep (Proxy :: Proxy ((->) Int))   == * -> *
 kindRep (Proxy :: Proxy Eq)           == * -> Constraint

 kindRep (Proxy :: Proxy (':))         insoluble
 kindRep (Proxy :: Proxy 'Just)        insoluble
 }}}

 I have not thought much about this might fit in to the new type-indexed
 `TypeRep`.

--
Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/10343#comment:26>
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