[GHC] #15760: Preserve parens in TH

[GHC]

#15760: Preserve parens in TH
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           Reporter:  goldfire       |             Owner:  (none)
               Type:  bug            |            Status:  new
           Priority:  normal         |         Milestone:
          Component:  Template       |           Version:  8.6.1
  Haskell                            |
           Keywords:                 |  Operating System:  Unknown/Multiple
       Architecture:                 |   Type of failure:  None/Unknown
  Unknown/Multiple                   |
          Test Case:                 |        Blocked By:
           Blocking:                 |   Related Tickets:
Differential Rev(s):                 |         Wiki Page:
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 Template Haskell supports parentheses in its AST. So does GHC. Yet GHC
 casually discards parentheses when desugaring TH quotes. We should
 preserve them.

 I was originally thinking that this could get rid of `Note [Adding parens
 for splices]` in Convert, but that processing would still be necessary if
 we are converting TH AST that did not come from a quote. Actually, it gets
 worse with this change, because we don't want to add ''redundant'' parens.

 Still, I think preserving parens is the right thing to do here. It also
 makes it possible for a client to give special meaning to, say, nested
 parens: Perhaps `process [| f x |]` and `process [| f ((x)) |]` will
 behave differently. (Idiom brackets, anyone?)

-- 
Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/15760>
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