startup.tjs

var alert = System.inform;

class RPNMachine {
    var m_stack = [];
    var m_ops = %[
        "+" => %[
            arity: 2,
            fn: function (stack) {
                stack.push(stack.pop() + stack.pop());
            },
        ],
        "-" => %[
            arity: 2,
            fn: function (stack) {
                stack.push(stack.pop() - stack.pop());
            },
        ],
        "*" => %[
            arity: 2,
            fn: function (stack) {
                stack.push(stack.pop() * stack.pop());
            },
        ],
        "/" => %[
            arity: 2,
            fn: function (stack) {
                var r = stack.pop();
                var l = stack.pop();
                if (r == 0)
                    throw new Exception("divide by zero");
                else
                    stack.push(l / r);
            },
        ],
        "." => %[
            arity: 1,
            fn: function (stack) {
                alert(stack.pop());
            },
        ],
    ];

    function checkArity(arity) {
        return m_stack.count >= arity;
    }

    function run(expr) {
        var r_sp = /\s+/;
        var r_number = /^\d+$/;
        var terms = r_sp.split(expr);
        for (var i = 0; i < terms.count; i++) {
            var t = terms[i];
            if (r_number.test(t)) {
                m_stack.push(+t);
            }
            else if (m_ops[t]) {
                if (!checkArity(m_ops[t].arity)) {
                    alert("[error] arity is less than arguments");
                    continue;
                }

                try {
                    m_ops[t].fn(m_stack);
                }
                catch (e) {
                    alert("[error] " + e.message);
                }
            }
        }
    }
}

var machine = new RPNMachine();
machine.run(System.inputString("RPNMachine", "Input RPN expression", "1 2 3 + + ."));

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