[GHC] #10177: Typeable solver regression

[GHC]

#10177: Typeable solver regression
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        Reporter:  glguy             |                   Owner:
            Type:  bug               |                  Status:  new
        Priority:  highest           |               Milestone:  7.10.1
       Component:  Compiler (Type    |                 Version:  7.10.1-rc3
  checker)                           |                Keywords:
      Resolution:                    |            Architecture:
Operating System:  Unknown/Multiple  |  Unknown/Multiple
 Type of failure:  GHC rejects       |               Test Case:
  valid program                      |  testsuite/tests/typecheck/should_compile/T10177
      Blocked By:                    |                Blocking:
 Related Tickets:                    |  Differential Revisions:
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Changes (by simonpj):

 * status:  closed => new
 * resolution:  fixed =>


Comment:

 Actually I really don't think this code should work.  It should be
 {{{
 instance (Typeable n, Typeable a) => C (V n a)
 }}}
 Otherwise there is an overlap between the given `(Typeable (V n))` and the
 built-in instance for `Typeable (V n a)`.   Making the code given here
 work is very fragile, and might depend on solve order.


 I vote that should fail.  Any dissenters?

 Simon

--
Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/10177#comment:5>
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