[GHC] #10079: Coercible solver regression: Couldn't match rep of () with Const () b

[GHC]

#10079: Coercible solver regression: Couldn't match rep of () with Const () b
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        Reporter:  glguy             |                   Owner:  goldfire
            Type:  bug               |                  Status:  merge
        Priority:  highest           |               Milestone:  7.10.1
       Component:  Compiler (Type    |                 Version:  7.10.1-rc1
  checker)                           |                Keywords:
      Resolution:                    |            Architecture:
Operating System:  Unknown/Multiple  |  Unknown/Multiple
 Type of failure:  GHC rejects       |               Test Case:  indexed-
  valid program                      |  types/should_compile/T10079
      Blocked By:                    |                Blocking:
 Related Tickets:                    |  Differential Revisions:
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Comment (by simonpj):

 No I can't remember why the inherited thing was done; but I think we can
 simplify it away anyway.

 Re new proposal, I'm worried about what happens if we have `f a ~ N b`,
 where N's data constructor is not in scope.  Then the
 `tcTopNormaliseNewTypeNF_maybe` thing won't fire, and we'll drop back into
 the `AppTy` case.... infinite loop.

 It doesn't smell good... code is too tricky.

 You don't comment about '''Third''' above; but it's another bug waiting to
 happen, isn't it?

 Simon

--
Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/10079#comment:11>
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