[GHC] #9732: Pattern synonyms and unboxed values

[GHC]

#9732: Pattern synonyms and unboxed values
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              Reporter:  monoidal    |            Owner:  cactus
                  Type:  bug         |           Status:  new
              Priority:  normal      |        Milestone:
             Component:  Compiler    |          Version:  7.8.3
            Resolution:              |         Keywords:
      Operating System:              |     Architecture:  Unknown/Multiple
  Unknown/Multiple                   |       Difficulty:  Unknown
       Type of failure:  Compile-    |       Blocked By:
  time crash                         |  Related Tickets:
             Test Case:              |
              Blocking:              |
Differential Revisions:              |
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Comment (by cactus):

 The problem with `pattern P = 0#` is that the wrapper it yields is `$WP =
 0#` which is a top-level binding at an unboxed type. If `P` had any
 arguments, then `$WP` would be a function instead of a variable, and so it
 would be valid. So we could say that unboxed pattern synonyms are only
 allowed if they are either unidirectional or have arguments. But doesn't
 that sound a bit arbitrary?

 Side question: is it even possible to change the definition of `P` to have
 an argument but still be unboxed? Something like `pattern P x = (# 0#, x
 #)` doesn't work, because unboxed tuples are not allowed in patterns.

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Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/9732#comment:6>
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