[GHC] #11081: Implement Introspective Template Haskell

[GHC]

#11081: Implement Introspective Template Haskell
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        Reporter:  goldfire          |                Owner:
            Type:  feature request   |               Status:  new
        Priority:  normal            |            Milestone:  ⊥
       Component:  Template Haskell  |              Version:  7.10.2
      Resolution:                    |             Keywords:
Operating System:  Unknown/Multiple  |         Architecture:
                                     |  Unknown/Multiple
 Type of failure:  None/Unknown      |            Test Case:
      Blocked By:                    |             Blocking:
 Related Tickets:                    |  Differential Rev(s):
       Wiki Page:                    |
  TemplateHaskell/Introspective      |
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Comment (by simonpj):

 I'm sceptical about the stuff about Core until I see more details.  But
 that's for the future.

 The fundamental idea here is to replace `Language.Haskell.TH.Syntax`
 outright with `HsSyn`.  The advantages, of course, are (a) avoiding
 duplication, (b) TH stop lagging GHC.

 The disadvantage is that `HsSyn` is designed as an internal data type for
 a compiler. We feel free to

 * decorate it with extra information (mostly types) as it moves down the
 pipeline,
 * have one constructor before type checking and a different one afterwards
 (eg `ConPatIn` and `ConPatOut` in `HsPat`
 * add elaboration info for type and dictionary applications and
 instantiation.

 For TH programs that construct syntax trees directly (ie not using
 quotation) or pattern-match over them, all this extra clutter might be
 confusing and/or awkward.

 I'm very unsure about the back-compat shim, but maybe it's possible. Yay
 for pattern synonyms.

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Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/11081#comment:5>
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