/*
* Returns a parser that for the grammar rule:
*
* minusTerm = '-' term;
*
* This parser has an assembler that will pop two
* numbers from the stack and push their difference.
*/
protected Parser minusTerm() {
Sequence s = new Sequence();
s.add(new Symbol('-').discard());
s.add(term());
s.setAssembler(new MinusAssembler());
return s;
}
/**
* Returns a parser that will recognize a Midimath expression.
*
* @return a parser that will recognize a Midimath expression
*/
public Parser expression() {
if (expression == null) {
expression = new Sequence();
expression.add(term());
expression.add(new Repetition(minusTerm()));
}
return expression;
}
/*
* Returns a parser that for the grammar rule:
*
* term = '(' expression ')' | Num;
*
* This parser adds an assembler to Num, that will
* replace the top token in the stack with the token's
* Double value.
*/
protected Parser term() {
Sequence s = new Sequence();
s.add(new Symbol('(').discard());
s.add(expression());
s.add(new Symbol(')').discard());
Alternation a = new Alternation();
a.add(s);
a.add(new Num().setAssembler(new NumAssembler()));
return a;
}