Using ANTLR4 in C# for building Expression trees

[Александр Кучеренко]

Hello everybody.

I'm trying to build Expression tree using ANTLR visitor in C#. ANTLR is used for parsing simple logical string like 'str1 OR str2'. From that string I want to get C# Expression<Func<String,bool>> so I can test if passed string matches conditions defined in logical string.
But after I call visit method on visitor as the result I get null, but in debug I can see that all my methods work as they should.
Could you please find problem in my code.
File "example usage.cs" contains sketch  of that I'm trying to achieve.
File "LogicalLangTreeVisitor.cs" contains my implementation of visitor.
File "LogicalLang.g4" contains my grammar.

[Sam Harwell]

Your example requires that expr be following by a newline character. In your sample input, no newline character is given, so the parse tree contains error nodes.

 

Also note that you didn’t provide an implementation for VisitProg or VisitStat in your visitor.

 

The default behavior for the visitor, in combination with error nodes appearing in your parse tree, is producing the null return value you are observing.

 

Sam

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[Александр Кучеренко]

Thanks for your comments. I have fixed my problem by adding new clause in stat rule for expr with no newline.


суббота, 22 марта 2014 г., 1:26:43 UTC+4 пользователь Sam Harwell написал: