Re: [GHC] #12045: Visible kind application

12 Sep 2016

      #12045: Visible kind application
-------------------------------------+-------------------------------------
        Reporter:  Iceland_jack      |                Owner:  Iceland_jack
            Type:  feature request   |               Status:  new
        Priority:  normal            |            Milestone:
       Component:  Compiler          |              Version:  8.1
      Resolution:                    |             Keywords:
                                     |  TypeApplications TypeInType
Operating System:  Unknown/Multiple  |         Architecture:
                                     |  Unknown/Multiple
 Type of failure:  None/Unknown      |            Test Case:
      Blocked By:                    |             Blocking:
 Related Tickets:                    |  Differential Rev(s):  Phab:D2216
       Wiki Page:                    |
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Comment (by Iceland_jack):

 {{{#!hs
 type Cat k = k -> k -> Type

 data FreeCat :: Cat k -> Cat k where
   Nil  :: FreeCat f a a
   Cons :: f a b -> FreeCat f b c -> FreeCat f a c

 liftCat :: f a b -> FreeCat f a b
 liftCat x = Cons x Nil
 }}}

 Free category generated by graph of natural numbers

 {{{#!hs
 data Node = Unit | N

 data NatGraph :: Cat Node where
   One  :: NatGraph Unit N
   Succ :: NatGraph N    N
 }}}

 {{{#!hs
 one :: (FreeCat @Node NatGraph) Unit N
 one = liftCat One
 }}}

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Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/12045#comment:7
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