// TODO: unary operators
sclass ShuntingYardCore<Op> {
  new L<Operator> operatorStack;
  
  void handleEOT() {
    while (nempty(operatorStack)) {
      var o = popLast(operatorStack);
      assertNequals(o, "(");
      outputQueue.add(o);
    }
  }

  void handleToken(S token) {
    if (iTok >= l(tok)) {
      false;
    }
    
    S t = tok.get(iTok);
    bool op = isOperator(t), space = isSpacer(t);
    if (op && space) warn("Operators should not be spacers");
    
    if (eq(t, "(")) {
      finishLiteral();
      operatorStack.add(t);
    } else if (eq(t, ")")) {
      finishLiteral();
      while (!eq(last(operatorStack), "(")) {
        assertNempty(operatorStack);
        outputQueue.add(popLast(operatorStack));
      }
      popLast(operatorStack);
    } else if (op) {
      finishLiteral();
      S o1 = t, o2;
      while (!eqOneOf(o2 = last(operatorStack), "(", null)
        && (precedence(o2) > precedence(o1)
        ||  precedence(o2) == precedence(o1) && isLeftAssociative(o1))) {
          ifdef ShuntingYardParser_debug
            print("popLast");
          endifdef
          outputQueue.add(popLast(operatorStack));
        }
        
      operatorStack.add(o1);
    }
    
    true;
  }
  
  // return 0 for non-operator
  int precedence(Op op) {
    ret 1;
  }
  
  swappable bool isLeftAssociative(Op op) { true; }
}