一个简单的词法分析器

最新推荐文章于 2025-06-10 08:55:25 发布

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最新推荐文章于 2025-06-10 08:55:25 发布

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分类专栏：前端相关

本文链接：https://blog.youkuaiyun.com/Grey_One/article/details/51547927

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input.html

<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <link rel="stylesheet" type="text/css" href="style.css">
    <title>Input</title>
</head>
<body>
<h1>简单词法分析器</h1>
<p>输入源程序：</p>
<textarea id="input" rows="10" cols="50"></textarea>
<br>
<button id="analysis" type="button" onclick="analysis()">分析</button>
<script type="text/javascript" src="analyzer.js"></script>
<pre id="output"> </pre>
</body>
</html>

analyzer.js

var state = 0;
var str = "";
var result = "";
var countdot = 0;
var counte = 0;
var line = 1;

//判断字母
function isChar(ch) {
    return (ch<='z')&&(ch>='a')||(ch<='Z')&&(ch>='A')&&(ch!='e');
}
//判断数字
function isDigit(ch){
    return (ch>='0')&&(ch<='9');
}
//判断运算符
function isOperator(ch) {
    return ch=="+"||ch=="-"||ch=="*"||ch=="/"||ch=="%"||ch=="="||ch=="<"||ch=="<";
}
//判断界符
function isDelimiter(ch){
    return ch==","||ch==";"||ch=="("||ch==")"||ch=="/*"||ch=="*/"||ch=="{"||ch=="}";
}

//判断空格
function isSpace(ch){
    return ch==' ';
}

//判断关键字
function isKey(str) {
    return str=="int"||str == "for"||str == "if"||str == "else"||str == "while"||str == "do"||str == "float"||
        str == "switch"||str == "case"||str == "default"||str=="char"||str=="void";
}
//判断下划线
function isUnderline(ch) {
    return ch=="_";
}
//判断美元符号
function isDollar(ch) {
    return ch=="$";

}
//判断小数点
function isdotted(ch) {
    return ch==".";

}
//判断科学计数法
function ise(ch) {
    return ch=="e";
}
//判断换行
function isEnter(ch) {
    return ch=="\n";

}
/*
 * 0：状态初始化
 * 1：关键字
 * 2：变量
 * 3：数字
 * 4：字符串
 * 5：运算符
 * 6：界符
 * */

function analysis(){
    line = 1;
    result = "";
    countdot = 0;
    counte = 0;
    var s = document.getElementById("input").value;
    for(var i=0;i<s.length;i++)
    {
        //console.log(s.charAt(i));
        var ch = s.charAt(i);
        switch (state){
            case 0:
                if(isChar(ch)||isDollar(ch)||isUnderline(ch)){
                    str = "" + ch;
                    state = 1;
                }
                else if(isDigit(ch)){
                    str = "" + ch;
                    state = 3;
                }
                else if(ch == '\"'){
                    str = "";
                    state = 4;
                }
                else if(isOperator(ch)){
                    str = "" + ch;
                    state = 5;
                    //console.log("<operator:"+ch+">");
                    result = result + "<operator:"+ch+">" + "\n";
                    state = 0;
                }
                else if(isDelimiter(ch)){
                    str = "" + ch;
                    state = 6;
                    //console.log("<delimiter:"+ch+">");
                    result = result + "<delimiter:"+ch+">" + "\n";
                    state = 0;
                }
                else if(isEnter(ch)){
                    line++;
                }
                break;
            case 1:
                if(isChar(ch)||isDigit(ch)||isUnderline(ch)){
                    str = str +ch;
                }else if(isDelimiter(ch)||isOperator(ch)||isSpace(ch)){
                    if(isKey(str)){
                        result = result + "<key:"+str+">" + "\n";
                    }else{
                        result = result + "<var:"+str+">" + "\n";
                    }
                    i--;
                    state = 0;
                }else{
                    result = result + "<error:"+str+">  " + line + "\n";
                    i--;
                    state = 0;
                }
                break;
            case 3:
                if(isDigit(ch)){
                    str = str + ch;
                }else if(isdotted(ch)){
                    countdot++;
                    if(countdot<2)
                        str = str + ch;
                    else
                        result = result + "error   " + line ;
                }else if(ise(ch)){
                    counte++;
                    if(counte<2)
                        str = str + ch;
                    else
                        result = result + "error   " + line ;
                }
                else if(isDelimiter(ch)||isOperator(ch)||isSpace(ch)){
                    result = result + "<number:"+str+">" + "\n";
                    i--;
                    state = 0;
                }else{
                    result = result + "<error:"+str+">  " + line + "\n";
                    i--;
                    state = 0;
                }
                break;
            case 4:
                if(ch == '\"'){
                    //console.log("<string:"+str+">");
                    result = result + "<string:"+str+">" + "\n";
                    state = 0;
                }else{
                    str = str + ch;
                }
                break;

        }
    }

    var o = document.getElementById("output");
    o.lastChild.nodeValue = result;
    
}

style.css

body{
    font-family: sans-serif;
}
h1{
    color:#699;
}
#output{
    color: blue;
    font-family: sans-serif;
    font-size: 16px;
}
#input{
    color: red;
    font-family: sans-serif;
    font-size: 16px;
}