[GHC] #10327: Devise workaround for how infinite types prevent closed type family reduction

[GHC]

#10327: Devise workaround for how infinite types prevent closed type family
reduction
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        Reporter:  goldfire          |                   Owner:
            Type:  feature request   |                  Status:  new
        Priority:  normal            |               Milestone:
       Component:  Compiler          |                 Version:  7.10.1
      Resolution:                    |                Keywords:
Operating System:  Unknown/Multiple  |            Architecture:
 Type of failure:  None/Unknown      |  Unknown/Multiple
      Blocked By:                    |               Test Case:
 Related Tickets:                    |                Blocking:
                                     |  Differential Revisions:
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Comment (by simonpj):

 I must be missing something.  `Inf f (f :+: g)` will certainly reduce for
 any ground `f` (such as `True` or `False`) because then the call will be
 apart from the first equation so the second can fire.

 If `f` is not ground, then it'll still reduce, if `f` is anything other
 than `f2 :+: g`, for the same reason.

 If `f` is a variable then yes the reduction is stuck, but that seems fair
 enough. Reducing it to {{{f `Seq` rhs}}} doesn't get us any further
 forward (e.g. if we want to unify this with another type) but it does add
 real new complication.

 Very unconvinced.

--
Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/10327#comment:2>
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