[GHC] #13324: Allow PartialTypeSignatures in the instance context of a standalone deriving declaration

[GHC]

#13324: Allow PartialTypeSignatures in the instance context of a standalone
deriving declaration
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        Reporter:  RyanGlScott       |                Owner:  (none)
            Type:  feature request   |               Status:  new
        Priority:  normal            |            Milestone:
       Component:  Compiler (Type    |              Version:  8.0.1
  checker)                           |
      Resolution:                    |             Keywords:
Operating System:  Unknown/Multiple  |         Architecture:
                                     |  Unknown/Multiple
 Type of failure:  None/Unknown      |            Test Case:
      Blocked By:                    |             Blocking:
 Related Tickets:  #10607            |  Differential Rev(s):
       Wiki Page:                    |
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Comment (by simonpj):

 Do you also, as #13415 implies, want the non-`deriving` case to work?
 {{{
 instance _ => C (T a) where
   op x = ...
   bop y = ...
 }}}
 This would be more ambitious, because you'd have to infer the constraints
 for the arbitrary user-written code in "...", and `TcInstDcls` isn't set
 up to do that.

 Remember that two instance declarations might both need each other. That's
 why there's a fixpoint in the deriving code.

 I think it'd be a lot easier to handle the deriving case than the general
 case.

--
Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/13324#comment:5>
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