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List:       antlr-interest
Subject:    [antlr-interest] Validating predicates in @after
From:       Felix Dorner <felix_do () web ! de>
Date:       2008-04-30 7:27:18
Message-ID: 48181F56.6040906 () web ! de
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Hey again..

In expression rules you often have alternatives that consist of 
subexpressions, like:

expression :
   |  ^(binop expression expression)
   |  ^(unaryop expression)
   ...

my current validation grammar looks like this:
  | ..
     ^(binop e1=expression e2=expression)
     {$e1.start.evalsTo != null}?
     {$e2.start.evalsTo != null}?
   | ^(unaryop e1=expression)
      {$e1.start.evalsTo != null}?

so there's a lot of repetitive code here. Rather than doing that, I'd 
like to verify right befor expression returns that its "evalTo" isn't 
null (i.e. it's a valid expression). Is this the only way to do this:?

@after {
if ($start.evalType() == null){
    throw new FailedPredicateException(input, expression, 
"$start.evalType != null");
}
}

Thanks again,
Felix




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