Interpreting a variable number of tree nodes in ANTLR Tree Grammar - antlr

Question

Whilst creating an inline ANTLR Tree Grammar interpreter I have come across an issue regarding the multiplicity of procedure call arguments.
Consider the following (faulty) tree grammar definition.
procedureCallStatement
: ^(PROCEDURECALL procedureName=NAME arguments=expression*)
{
if(procedureName.equals("foo")) {
callFooMethod(arguments[0], arguments[1]);
}elseif(procedureName.equals("bar")) {
callBarMethod(arguments[0], arguments[1], arguments[2]);
}
}
;
My problem lies with the retrieval of the given arguments. If there would be a known quantity of expressions I would just assign the values coming out of these expressions to their own variable, e.g.:
procedureCallStatement
: ^(PROCEDURECALL procedureName=NAME argument1=expression argument2=expression)
{
...
}
;
This however is not the case.
Given a case like this, what is the recommendation on interpreting a variable number of tree nodes inline within the ANTLR Tree Grammar?

Answer 1

Use the += operator. To handle any number of arguments, including zero:
procedureCallStatement
: ^(PROCEDURECALL procedureName=NAME argument+=expression*)
{
...
}
;
See the tree construction documentation on the antlr website.
The above will change the type of the variable argument from typeof(expression) to a List (well, at least when you're generating Java code). Note that the list types are untyped, so it's just a plain list.
If you use multiple parameters with the same variable name, they will also create a list, for example:
twoParameterCall
: ^(PROCEDURECALL procedureName=NAME argument=expression argument=expression)
{
...
}
;