Question

I have a simple grammar using Antlr 3:

grammar i;

@header {
package com.data;
}

null        : 'null';
value       : null | STRING;
elements    : value? | (value ',' value)+;
STRING      : ('a'..'z'|'A'..'Z')+;
WS      : (' '|'\t'|'\f'|'\n'|'\r')+ {skip();}; // handle white space between keywords

What I am trying to achive is I have a value. So a value can be optional or value follows a comma follwed by another value. So for example:

value could be true or value could be true, true, true, true.

When I do the interpretation the following works:

true

or
true , true

When I trying true, true, true the tree is displayed with true, true but shows a NoViableAltException.

I have also tried:

elements: value? | (value ',' value)*;

but this doesn’t work either.

Any ideas where I am going wrong?

EDIT:

insert      : 'INSERT INTO TABLE' 'VALUES' '('elements')'';';

Answer 1

The elements rule is written such that it derives only zero or one value, or any number of pairs that are separated by a comma, with no comma between the pairs.

Apparently what you want is this:

elements: ( value ( ',' value )* )?;

This allows for nothing at all (due to the ? operator), or a single value followed by zero or more (*) occurrences of a comma and a value.