function lex() {
	                var token;
	                token = self.lexer.lex() || 1;
	                if (typeof token !== "number") {
	                    token = self.symbols_[token] || token;
	                }
	                return token;
	            }
Returns the generated line and column information for the original source,
line, and column positions provided. The only argument is an object with
the following properties:

  - source: The filename of the original source.
  - line: The line number in the original source.  The line number
    is 1-based.
  - column: The column number in the original source.  The column
    number is 0-based.

and an object is returned with the following properties:

  - line: The line number in the generated source, or null.  The
    line number is 1-based. 
  - column: The column number in the generated source, or null.
    The column number is 0-based.