[GHC] #15905: Data familes should end in Type

[GHC]

#15905: Data familes should end in Type
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        Reporter:  simonpj           |                Owner:  (none)
            Type:  bug               |               Status:  new
        Priority:  normal            |            Milestone:  8.6.3
       Component:  Compiler          |              Version:  8.6.2
      Resolution:                    |             Keywords:
Operating System:  Unknown/Multiple  |         Architecture:
                                     |  Unknown/Multiple
 Type of failure:  None/Unknown      |            Test Case:
      Blocked By:                    |             Blocking:
 Related Tickets:  #14645            |  Differential Rev(s):
       Wiki Page:                    |
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Comment (by simonpj):

 My point is that the status quo is extremely fragile -- it relies
 crucially on eager unification.  It's supposed to be the case that we can
 defer all unifications to the constraint solver, all all will work.  But
 not so!  So now, to give a precise spec, we have to make precise which
 constraints can be solved eagerly and which can be deferred.  I hate that.

 The baby is mingled with the bathwater -- it's a fluke that it works at
 all.

-- 
Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/15905#comment:4>
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