[GHC] #13290: Data constructors should not have RULES

[GHC]

#13290: Data constructors should not have RULES
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        Reporter:  simonpj           |                Owner:  dfeuer
            Type:  bug               |               Status:  new
        Priority:  normal            |            Milestone:
       Component:  Compiler          |              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:  #7398             |  Differential Rev(s):
       Wiki Page:                    |
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Comment (by rwbarton):

 For what it's worth the documentation implicitly disallows these rules
 already, as it says

 > The left hand side of a rule must consist of a top-level variable
 applied to arbitrary expressions.

 and "variable" is used in the Haskell Report to refer to lowercase things,
 not constructors. Of course explicit is better than implicit, and probably
 the author of that sentence was not thinking about the case of
 constructors at the time.

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Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/13290#comment:6>
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