[GHC] #7730: :info and polykinds

[GHC]

#7730: :info and polykinds
--------------------------------------------+------------------------------
        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
--------------------------------------------+------------------------------

Comment (by archblob):

 I started implementing this and printing through ``` IfaceDecl ```
 directly as you suggested is the easier way and it turns out we don't
 really need to add any more information, all we need for printing properly
 is already there.

 Now before I go any further we need to discuss the approach I have taken
 and if it needs changing. Right now I'm exporting ``` pprIfaceDecl ```
 from ``` IfaceSyn ``` and I've modified  it to look like this ```
 pprIfaceDecl :: Maybe ShowSub -> IfaceDecl -> SDoc ``` this allows us to
 decide how we print things, if the first argument is ``` Nothing ``` we
 print ``` IfaceDecl ``` the old way. This will polute the ``` IfaceDecl
 ``` printing function with stuff destined for GHCi printing but it has the
 advantage that there are a lot of places where the printing is the same
 and a lot of code from pprTyThing will no longer be necessary.

 Another aproach is to write a separate ``` IfaceDecl ``` printing function
 for use in GHCi, but while keeping things separate this will lead to a lot
 of duplication.

 If you think that I should take the second aproach, or another that I did
 not consider please tell me and I will implement it.

 Thank you,

 Andrei

--
Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/7730#comment:13>
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