11 lines
400 B
Markdown
11 lines
400 B
Markdown
# Actions and semantic predicates
|
|
|
|
## How do I test if an optional rule was matched?
|
|
|
|
For optional rule references such as the initialization clause in the following
|
|
|
|
```
|
|
decl : 'var' ID (EQUALS expr)? ;
|
|
```
|
|
|
|
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. |