Question

I have an ANTLR grammar and am defining a function in my language that allows an optional parameter. How can I check whether the optional parameter is passed in or not within the code generation block?

I’m basically looking for the syntax to do something like this hypothetical tree grammar statement:

myFunc returns [int retval] : 'myFunc' arg1=number arg2=string?
{
    // Check if arg2 exists.
    if (/* arg2 exists */) { $retval = $arg1.value + 10; }
    else { $retval = $arg1.value; }
}

Any suggestions or pointers to documentation are greatly appreciated!

Answer 1

You should be able to just check if arg2 != null.