Java Advent Calendar 2011 code 7

Parser.jj

PARSER_BEGIN (Parser)
public class Parser {
}
PARSER_END (Parser)

SKIP: {
	" "
}
TOKEN: {
	<INTEGER: (["0"-"9"])+>
	| <PLUS: "+">
	| <MINUS: "-">
	| <NL: "\r\n" | "\n" | "\r">
}

void List(): {
	int val;
} {
	val = Expression() <NL> {
		System.out.println(val);
	}
}
int Expression(): {
	int val1;
	int val2;
} {
	val1 = PrimaryExpression() (
		<PLUS> val2 = PrimaryExpression() {
			val1 += val2;
		}
		| <MINUS> val2 = PrimaryExpression() {
			val1 -= val2;
		}
	)* {
		return val1;
	}
}
int PrimaryExpression(): {
	Token token;
} {
	token = <INTEGER> {
		return Integer.parseInt(token.image);
	}
}