[GHC] #393: functions without implementations

[GHC]

#393: functions without implementations
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        Reporter:  c_maeder          |            Owner:  simonpj
            Type:  feature request   |           Status:  new
        Priority:  normal            |        Milestone:  _|_
       Component:  Compiler (Type    |          Version:  None
  checker)                           |         Keywords:
      Resolution:  None              |     Architecture:  Unknown/Multiple
Operating System:  Unknown/Multiple  |       Difficulty:  Moderate (less
 Type of failure:  None/Unknown      |  than a day)
       Test Case:                    |       Blocked By:
        Blocking:                    |  Related Tickets:
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Comment (by simonpj):

 I suggest
  * A language extension flag `-XUndefinedFunctions` or something
  * In the renamer you'll have to arrange to create a binder for a
 signature that lacks a corresponding binding; and give an warning (rather
 than an error) for such signatures.
  * I suggest that you actually add the definition `f = error "Missing
 definition for f"` (or whatever) in the desugarer.  GHC generally tries
 NOT to mess with the source code until desugaring, so that you can always
 show exactly what the user wrote.

 Happy to discuss when you get a bit further

 Simon

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Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/393#comment:16>
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