[GHC] #9813: Error when reifying type constructor

[GHC]

#9813: Error when reifying type constructor
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        Reporter:  owst              |                Owner:
            Type:  bug               |               Status:  new
        Priority:  normal            |            Milestone:
       Component:  Template Haskell  |              Version:  7.8.3
      Resolution:                    |             Keywords:
Operating System:  Unknown/Multiple  |         Architecture:
                                     |  Unknown/Multiple
 Type of failure:  None/Unknown      |            Test Case:
      Blocked By:                    |             Blocking:
 Related Tickets:                    |  Differential Rev(s):  Phab:D1899
       Wiki Page:                    |
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Comment (by owst):

 I think it's reasonable to expose the toposort of declarations - users are
 presumably used to declarations not being processed top-to-bottom already;
 it seems more consistent to expose toposorted-ness here too, rather than
 use a different rule.

 Some thoughts about your proposal (which I like the gist of!):
 * W.r.t. step 1. I'd quite like the splice in {{{f}}}:
     {{{#!hs
     f x = x ++ $(reify 'g ...)

     $(return [])

     g x = x + 1
     }}}
  to be able to refer to {{{g}}}. It is in a different declaration group,
 but I think that it should be visible. However, I can't see an easy way
 around the need for declaration groups, so maybe it's not possible.
 * In step 2. I think it would be necessary that a splice within a
 declaration cannot refer to the declaration itself (though I'm not
 ''sure'' this is a problem?)


 > No code that is accepted today would be rejected by these rules.
 This seems particularly desirable to me!

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Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/9813#comment:16>
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