11 lines
400 B
Markdown
11 lines
400 B
Markdown
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# Actions and semantic predicates
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## How do I test if an optional rule was matched?
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For optional rule references such as the initialization clause in the following
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```
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decl : 'var' ID (EQUALS expr)? ;
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```
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testing to see if that clause was matched can be done using `$EQUALS!=null` or `$expr.ctx!=null` where `$expr.ctx` points to the context or parse tree created for that reference to rule expr.
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