[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 goldfire):

 Replying to [comment:2 simonpj]:
 > Very unconvinced.

 As, rest assured, am I.

 I think to get this to work we would also need a constraint `Finite f`
 that means (via magic) that {{{f `Seq` x}}} reduces to `x`. (Without
 magic, this would be spelled {{{forall x. f `Seq` x ~ x}}}, but that's a
 higher-order constraint!)

 But to really get it to work, we need a totally different idea, as this
 one is terrible.

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Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/10327#comment:3>
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