[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:  7.8.3
       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 simonpj):

 Re recursive flags, promotable, etc, the usual convention is to print that
 kind of stuff when `-dppr-debug` is enabled.  Let's just do that for now.

 I was expecting you to say that a type like `Ord a => a -> Bool` is
 printing as `Ord a -> a -> Bool`, which isn't what the user of GHCi
 expects.  Isn't that happening?  To solvet hat I propose that we add a new
 constructor `IfaceDFunTy` to `IfaceType`, that behaves exactly like
 `IfaceFunTy` except that it prints differently.

 Re (2) that's an example of a bump in the road, and one I was expecting.
 I think it amounts to saying that the `ifAxiom` field of the `IfaceData`
 constructor doesn't have enough information to print nicely.

 One possibility is to add that information; it's kind of redundant (in the
 same way as `IfaceDFunTy`, but helps printing. But first, why are we
 calling `pprTyThing` on a family instance tycon? Does this case show up in
 practice? If so, how? I'd expect it to be more common to print a
 `IfaceFamInst`.

 Simon

--
Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/7730#comment:21>
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