[GHC] #15828: Type family equation foralls allow strange re-quantification of class-bound type variables

[GHC]

#15828: Type family equation foralls allow strange re-quantification of class-bound
type variables
-------------------------------------+-------------------------------------
        Reporter:  RyanGlScott       |                Owner:  (none)
            Type:  bug               |               Status:  new
        Priority:  normal            |            Milestone:  8.8.1
       Component:  Compiler          |              Version:  8.7
      Resolution:                    |             Keywords:  TypeFamilies
Operating System:  Unknown/Multiple  |         Architecture:
                                     |  Unknown/Multiple
 Type of failure:  None/Unknown      |            Test Case:
                                     |  rename/should_fail/T15828
      Blocked By:                    |             Blocking:
 Related Tickets:                    |  Differential Rev(s):  Phab:D5283
       Wiki Page:                    |
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Comment (by Simon Peyton Jones <simonpj@…>):

 In [changeset:"5b7ca03995c1d5fbd29ba0e327bb2a1f344c9419/ghc"
 5b7ca039/ghc]:
 {{{
 #!CommitTicketReference repository="ghc"
 revision="5b7ca03995c1d5fbd29ba0e327bb2a1f344c9419"
 Wibble to Taming the Kind Inference Monster

 I had allowed rename/should_fail/T15828 (Trac #15828) to regress a bit.
 The main payload of this patch is to fix that problem, at the cost of
 more contortions in checkConsistentFamInst.  Oh well, at least they are
 highly localised.

 I also update the -ddump-types code in TcRnDriver to print out some
 more expicit information about each type constructor, thus instead of

    DF{3} :: forall k. * -> k -> *

 we get

    data family DF{3} :: forall k. * -> k -> *

 Remember, this is debug-printing only.  This change is the reason
 that so many .stderr files change.
 }}}

-- 
Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/15828#comment:12>
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