[GHC] #9182: Empty case analysis for function clauses

[GHC]

#9182: Empty case analysis for function clauses
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       Reporter:  dfranke           |             Owner:
           Type:  feature request   |            Status:  new
       Priority:  low               |         Milestone:
      Component:  Compiler          |           Version:  7.8.2
       Keywords:                    |  Operating System:  Unknown/Multiple
   Architecture:  Unknown/Multiple  |   Type of failure:  None/Unknown
     Difficulty:  Unknown           |         Test Case:
     Blocked By:                    |          Blocking:
Related Tickets:                    |
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 Thanks to `-XEmptyCase`, the following is legal:

 {{{
   module Empty where

   data Empty

   empty :: Empty -> a
   empty x = case x of { }
 }}}

 However, if I leave off the last line, GHC will complain that `The type
 signature for ‘empty’ lacks an accompanying binding`.

 I think this program should be accepted. It isn't that I'm not giving a
 definition for `empty`; it's that I'm defining it to be a function with no
 accompanying equations, as could be represented in Template Haskell by

   $(return [FunD (mkName "empty") []])

 Currently, this too is rejected, with GHC complaining `Function binding
 for ‘empty’ has no equations`. I think this should be legal, with an empty
 list of clauses in a function definition being treated the same way as an
 empty list of matches in a case expression.

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Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/9182>
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