Is it possible to add TOKEN automatically if conditional Token is absent

[Edgar Buchvalov]

lessExpression: attribute lt dr=value? {if($ctx.dr==null) "somehow add predefined value to expression" };

If it is possible that when I enter:
"attr < 5" in java tree visitor I will get 5 when visiting valueContext, but
"attr < " will still visit valueContext, but with value ?.

is it possible to make such condition in rule file?

[John B. Brodie]

Greetings!

Recall that the `?` meta operator is antlr sugar for the empty alternative. that is x? is the same as (x|) which i like to write as (x|/*empty*/) making the empty choice more explicit to a human reader.

And so you should use the expanded form and insert whatever action you need in the empty alternative. Something like:

lessExpression: attribute lt (dr=value | /*empty*/ { dr=predefinedDefaultValue } );

Hope this helps...

   -jbb

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[Jim Idle]

In your listener or visitor, just check if ctx.dr == null. If it does, then you know to add your predefined value in to the mix. I would try to keep all actions out of the parser grammar itself.

Jim

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