Problem with sablecc on production rule of the form prod = (expr | expr')*

Question

Productions
    program = cls*;
    cls = clsdef name openbrace clsdata closingbrace;
    clsdata = (clsfield|clsmethod)*;
    clsfield = [variabletype]:name [variablename]:name semi;
    clsmethod = [returntype]:name [methodname]:name openmethodbrace closingmethodbrace openbrace closingbrace;

The problem resides in

clsdata = (clsfield|clsmethod)*;

If I set clsdata to

clsdata = clsfield*;

or to

clsdata = clsmethod*;

it works fine, though, as you can imagine, it doesn't mean the same thing as what I intended it to. I want a class to allow for both methods and fields (in no specific order!).

So my question is in how should I define clsdata so that I don't get errors. I can think of recursive alternatives, but I'd like to keep this as clean as possible!

Thanks

Answer 1

clsdata = (clsfield|clsmethod)*;

SableCC has an EBNF like syntax, but does not support this type of grammar rule. As you've already done, the non-terminal alternatives clsfield and clsmethod need be refractored into their own production.

yet I am not sure this is the best way to do this

If you look at any of the SableeCC example grammars you'll see that is the standard way of defining 'class members'. Although you could perhaps simplify your grammar by removing clsmembers:

Productions
    program = cls*;
    cls = clsdef name openbrace clsmember* closingbrace;
    clsmember = {clsfield} clsfield | {clsmethod} clsmethod;
    clsfield = [variabletype]:name [variablename]:name semi;
    clsmethod = [returntype]:name [methodname]:name openmethodbrace closingmethodbrace openbrace closingbrace

Answer 2

This works:

Productions
    program = cls*;
    cls = clsdef name openbrace clsmembers closingbrace;
    clsmembers = clsmember*;
    clsmember = {clsfield} clsfield | {clsmethod} clsmethod;
    clsfield = [variabletype]:name [variablename]:name semi;
    clsmethod = [returntype]:name [methodname]:name openmethodbrace closingmethodbrace openbrace closingbrace;

yet I am not sure this is the best way to do this. I welcome other approaches!