Lua逆波兰求值：后缀表达式的栈式计算

-- 错误：从左到右顺序求值，乘加同级
local v = 3
v = v + 4
v = v * 2
-- 得 14，而数学答案应为 11

local function evalRPN(tokens)
    local stack = {}
    for _, tk in ipairs(tokens) do
        if tonumber(tk) then
            stack[#stack + 1] = tonumber(tk)
        else
            local b = table.remove(stack)
            local a = table.remove(stack)
            if tk == "+" then
                stack[#stack + 1] = a + b
            elseif tk == "*" then
                stack[#stack + 1] = a * b
            end
        end
    end
    return stack[1]
end
local label = panel:getChildByName("exprText")
label:setString(tostring(evalRPN({"3", "4", "+", "2", "*"})))