[GHC] #12249: Template Haskell top level scoping error

[GHC]

#12249: Template Haskell top level scoping error
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        Reporter:  simonpj           |                Owner:
            Type:  bug               |               Status:  new
        Priority:  normal            |            Milestone:
       Component:  Template Haskell  |              Version:  8.0.1
      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:                    |
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Comment (by goldfire):

 Hm. I suppose I've run into the same issue when writing `singletons`. But
 isn't this what `newName` is for? Currently, `newName` doesn't always do a
 good enough job at creating a top-level name that's fresh even between
 splices, but I'm sure we could fix it.

 In effect, you're trying to turn TH into a module/namespace system, where
 some apparently-top-level declarations actually have a limited scope.
 Whether or not a definition is local or global depends on the entire file,
 instead of being listed in one spot. While what you propose may be readily
 implementable, I would say that it may be time better spent designing a
 proper module/namespace system that TH could use.

 As you've designed this feature, I could see people (perhaps even
 including myself) using TH only for your new module-like capabilities. For
 example, when writing papers, I often use the same variable names in
 different examples. When I extract my code and compile the papers, these
 overlapping variable names cause annoyance. If you implement your feature,
 then I would put some TH dingbats in my extraction engine to avoid the
 ambiguous variable uses/redefinitions... but this is abusive of TH.
 Clearly, compiling academic papers is not the primary use-case for Haskell
 (or is it? I suppose it once was!) but I'm sure I'm not the only one who
 would do such shenanigans.

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Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/12249#comment:5>
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