applescript计算器不起作用

我做了一个计算器，它应该可以工作，但是不可以。唯一起作用的部分是添加。这是我的代码：

   my Calculator()
on Calculator()
    display dialog "Calculator" buttons {"Add", "Multiply", "Divide"}
    if button returned of the result is "Add" then
        display dialog "What plus What?" default answer ""
        set a to (text returned of result)
        if a is equal to "q" then
            return
        end if
        display dialog "Next number" default answer ""
        set b to (text returned of result)
        set c to a + b
        display dialog "The answer is " & c buttons {"Start Again", "Quit"}
        if button returned of the result is "Quit" then
            return
        else
            my Calculator()
        end if
    end if
    if button returned of the result is "Multiply" then
        display dialog "What times what?" default answer ""
        set a to (text returned of result)
        if a is equal to "q" then
            return
        end if
        display dialog "Next number" default answer ""
        set b to (text returned of result)
        set c to a * b
        display dialog "The answer is " & c buttons {"Start Again", "Quit"}
        if button returned of the result is "Quit" then
            return
        else
            my Calculator()
        end if
    end if
    if button returned of the result is "Divide" then
        display dialog "What divided by what?" default answer ""
        set a to (text returned of result)
        if a is equal to "q" then
            return
        end if
        display dialog "Next number" default answer ""
        set b to (text returned of result)
        set c to a / b
        display dialog "The answer is " & c buttons {"Start Again", "Quit"}
        if button returned of the result is "Quit" then
            return
        else
            my Calculator()
        end if
    end if
end Calculator
end
   end

它是一个applescript代码。抱歉，这是一个nooby问题，但我需要帮助。谢谢！