一个简单的词法分析器

来源：互联网发布：优行科技知乎编辑：程序博客网时间：2024/06/06 02:47

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;}

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