Applescript “如何显示对话框”；“错误”；当变量返回错误答案时

好的，我的代码在下面，当我输入一个拼写错误的单词或一个没有意义的短语时，它会显示一个带有“msng”的对话框，但我想显示一条错误消息。如果答案是/包含“msng”，我尝试使用这两种答案，然后。。。但这是行不通的，任何帮助都是感激的

tell application "Safari"
    quit
end tell

set defaultAnswer to ""
set cancelButton to "Cancel"
set buttonResearch to "ReSearch"

display dialog "Query: " default answer defaultAnswer buttons {cancelButton, buttonResearch} default button buttonResearch cancel button cancelButton with icon 1
copy the result as list to {button_pressed, text_returned}

tell application "Dragon Dictate"
    set listening to false
end tell

if (button_pressed is buttonResearch) and (text_returned is not "") then
    set theUrl to "http://www.wolframalpha.com/input/?i=" & encode_text(text_returned, true, false)
    tell application "Safari"
        tell window 1 to set current tab to (make new tab with properties {URL:theUrl})
        tell me to say "let me look that up for you now"
        tell document 1
            repeat -- wait until loaded
                delay 2
                if (do JavaScript "document.readyState") = "complete" then exit repeat
            end repeat
            do JavaScript "document.getElementById('pod_0200').getElementsByClassName('action subpod-copyablept ')[0].click()" -- show the popup window
            set theAnswer to do JavaScript "document.body.lastChild.getElementsByTagName('pre')[0].innerHTML;" -- get the answer in this popup window
        end tell
    end tell
    activate

    if theAnswer contains "msng" then
        display dialog "There was an error, you may have misspelled a word or phrased it incorrectly"
    else
        display dialog theAnswer
    end if

end if

tell application "Safari"
    quit
end tell

-- encoding high-ASCII characters:
on encode_char(this_char)
    set the ASCII_num to (the ASCII number this_char)
    set the hex_list to {"0", "1", "2", "3", "4", "5", "6", "7", "8", "9", "A", "B", "C", "D", "E", "F"}
    set x to item ((ASCII_num div 16) + 1) of the hex_list
    set y to item ((ASCII_num mod 16) + 1) of the hex_list
    return ("%" & x & y) as string
end encode_char

-- TEXT ENCODING: encode spaces and high-level ASCII characters (those above 127)
-- encode_URL_A = encode most of the special characters reserved for use by URLs.
on encode_text(this_text, encode_URL_A, encode_URL_B)
    set the standard_characters to "abcdefghijklmnopqrstuvwxyz0123456789"
    set the URL_A_chars to "$+!'/?;&@=#%><{}[]\"~`^\\|*"
    set the URL_B_chars to ".-_:"
    set the acceptable_characters to the standard_characters
    if encode_URL_A is false then set the acceptable_characters to the acceptable_characters & the URL_A_chars
    if encode_URL_B is false then set the acceptable_characters to the acceptable_characters & the URL_B_chars
    set the encoded_text to ""
    repeat with this_char in this_text
        if this_char is in the acceptable_characters then
            set the encoded_text to (the encoded_text & this_char)
        else
            set the encoded_text to (the encoded_text & encode_char(this_char)) as string
        end if
    end repeat
    return the encoded_text
end encode_text

告诉应用程序“Safari”
退出
结束语
将defaultAnswer设置为“”
将取消按钮设置为“取消”
将按钮ReSearch设置为“ReSearch”
显示对话框“查询：”默认回答默认回答按钮{cancelButton，buttonResearch}默认按钮按钮搜索取消按钮取消按钮图标1
将结果作为列表复制到{按下按钮，返回文本}
告诉应用程序“龙口述”
将侦听设置为false
结束语
如果（按下的按钮是buttonResearch）和（返回的文本不是“”），则
将URL设置为“http://www.wolframalpha.com/input/?i=编码文本（返回的文本，真，假）（&encode）
告诉应用程序“Safari”
告诉窗口1将当前选项卡设置为（使用属性{URL:theUrl}创建新选项卡）
告诉我说“让我现在帮你查一下”
告诉文件1
重复--等待加载
延迟2
如果（do JavaScript“document.readyState”）=“complete”，则退出repeat
结束重复
执行JavaScript“document.getElementById（'pod_0200'）。getElementsByCassName（'action subpod copyablept'）[0]。单击（）”--显示弹出窗口
将答案设置为执行JavaScript“document.body.lastChild.getElementsByTagName（'pre'）[0].innerHTML；”--在该弹出窗口中获取答案
结束语
结束语
激活
如果答案包含“msng”，则
显示对话框“出现错误，您可能拼写错误或措辞不正确”
其他的
显示回答对话框
如果结束
如果结束
告诉应用程序“Safari”
退出
结束语
--编码高ASCII字符：
关于编码字符（此字符）
将ASCII_num设置为（此字符的ASCII编号）
将十六进制列表设置为{“0”、“1”、“2”、“3”、“4”、“5”、“6”、“7”、“8”、“9”、“A”、“B”、“C”、“D”、“E”、“F”}
将x设置为十六进制列表的项目（（ASCII_num div 16）+1）
将y设置为十六进制列表的项（（ASCII数mod 16）+1）
以字符串形式返回（“%”&x&y）
结束编码字符
--文本编码：对空格和高级ASCII字符（127以上的字符）进行编码
--encode_URL_A=对URL保留使用的大多数特殊字符进行编码。
在encode_text（此_text，encode_URL_A，encode_URL_B）上
将标准字符设置为“abcdefghijklmnopqrstuvwxyz0123456789”
将URL_A_chars设置为“$+！”/？；&@=#%>使用

因为
«class msng»
是缺失值的原始AppleScript代码

显示对话框
命令显示该类的名称-->“msng”
谢谢，我是新手！
if theAnswer is missing value then
    display dialog "There was an error, you may have misspelled a word or phrased it incorrectly"
else
    display dialog theAnswer
end if