[GHC] #12553: Reference kind in a type instance declaration defined in another instance declaration

[GHC]

#12553: Reference kind in a type instance declaration defined in another instance
declaration
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        Reporter:  Iceland_jack      |                Owner:
            Type:  bug               |               Status:  new
        Priority:  normal            |            Milestone:
       Component:  Compiler          |              Version:  8.0.1
      Resolution:                    |             Keywords:  TypeInType
Operating System:  Unknown/Multiple  |         Architecture:
                                     |  Unknown/Multiple
 Type of failure:  None/Unknown      |            Test Case:
      Blocked By:                    |             Blocking:
 Related Tickets:                    |  Differential Rev(s):
       Wiki Page:                    |
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Comment (by goldfire):

 I think the following clarifying comment might help:

 When declaring a type family like

 {{{
 type family F a :: u
 }}}

 the result kind `u` is actually a ''parameter'' to `F`. This type family
 is the same as

 {{{
 type family G u a :: u
 }}}

 except that in `F`, the `u` is invisible. So there are no existential
 kinds involved.

 Does this help?

--
Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/12553#comment:9>
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