[GHC] #10796: Illegal data constructor name: `fromList' ... When splicing a TH expression

[GHC]

#10796: Illegal data constructor name: `fromList' ... When splicing a TH expression
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        Reporter:  erisco            |                Owner:
            Type:  bug               |               Status:  new
        Priority:  normal            |            Milestone:  8.0.1
       Component:  Template Haskell  |              Version:  7.8.3
      Resolution:                    |             Keywords:  newcomer
Operating System:  Unknown/Multiple  |         Architecture:
                                     |  Unknown/Multiple
 Type of failure:  None/Unknown      |            Test Case:
      Blocked By:                    |             Blocking:
 Related Tickets:                    |  Differential Rev(s):
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Comment (by RyanGlScott):

 One thing isn't clear to me about the changes proposed. We could certainly
 modify `dataToQa` so that `dataToExpQ` (and thus `liftData`) works with
 both function and constructor names. What about `dataToPatQ`, though?
 There's no way to pattern-match on an expression directly, so what would
 this translate to?

 {{{#!hs
 f :: Set Char -> Set Char
 f s@($(dataToPatQ (const Nothing) (fromList "test"))) = s
 }}}

 The only way I could envision this working is if it were translated to
 something like:

 {{{#!hs
 f :: Set Char -> Set Char
 f x | x == fromList "test" = x
 }}}

 which is reminiscent of how pattern-matching on literals works, I suppose.

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Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/10796#comment:6>
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