From: gneuner2@comcast.net   
      
   On 23 Mar 2007 22:16:22 -0400, royzlife@gmail.com wrote:   
      
   >Can any one help in explaining how to negate a production rule in   
   >Bison parser?   
   >e.g  A:B   
   >      B: C   
   >          |D   
   >          |E   
   >  (here i want to write a block of statements or rules which will be   
   >executed if B doesnt match to C/D/E.)   
   >   
   >[Basically, you can't other than by enumerating all of the other   
   >possibilities.  What do you really want to do here? -John]   
      
   There is no way to specify the complement of a rule because it isn't a   
   terribly useful thing to do.  Context free languages are drawn from an   
   infinite set of strings, the complement of any particular subset of a   
   language is also an infinite set of strings.  Not very practical to   
   match.   
      
   If you can tell us more about what you are trying to do, we might be   
   able to suggest some alternatives.   
      
   George   
      
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