[GHC] #12778: Expose variables bound in quotations to reify

[GHC]

#12778: Expose variables bound in quotations to reify
-------------------------------------+-------------------------------------
        Reporter:                    |                Owner:  (none)
  facundo.dominguez                  |
            Type:  bug               |               Status:  patch
        Priority:  normal            |            Milestone:
       Component:  Template Haskell  |              Version:  8.0.1
      Resolution:                    |             Keywords:  template-
                                     |  haskell reify
Operating System:  Unknown/Multiple  |         Architecture:
                                     |  Unknown/Multiple
 Type of failure:  None/Unknown      |            Test Case:
      Blocked By:                    |             Blocking:
 Related Tickets:                    |  Differential Rev(s):  Phab:D3003
       Wiki Page:                    |
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Comment (by facundo.dominguez):

 Another way to address this. We make
 {{{
 $([| let x = True in $(q) |])
 }}}
 desugar to
 {{{
 $(return (LetE [ x = True ] (Splice q)))
 }}}
 where `Splice :: Q Exp -> Exp` is a new constructor of the datatype
 `Language.Haskell.TH.Syntax.Exp`.

 The compiler runs first the outer splice which becomes
 {{{
 let x = True in $(q)
 }}}
 and then it runs the inner splice $(q) as if it were a regular top-level
 splice.

 Pros: It makes inner splices work pretty much as outer splices.
 Cons: This probably is a bigger change in the compiler (hopefully not too
 big).

--
Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/12778#comment:11>
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