[GHC] #7730: :info and polykinds

[GHC]

#7730: :info and polykinds
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        Reporter:  monoidal                 |            Owner:  archblob
            Type:  bug                      |           Status:  new
        Priority:  normal                   |        Milestone:  7.8.1
       Component:  Compiler (Type checker)  |          Version:  7.6.2
      Resolution:                           |         Keywords:
Operating System:  Unknown/Multiple         |     Architecture:
 Type of failure:  None/Unknown             |  Unknown/Multiple
       Test Case:                           |       Difficulty:  Unknown
        Blocking:                           |       Blocked By:
                                            |  Related Tickets:  #8776
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Comment (by archblob):

 We could also just use ``` tyThingToIfaceDecl ``` and keep printing
 ```TyThing`` using the existing code and just replace the type variables
 with the ones we extract from ``` IfaceDecl ``` . This fix would be just a
 few lines but it seems rather hackish and wasteful.

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Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/7730#comment:14>
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