// 实验存档
输入示例
main()
{
int a, b;
a = ;
b = a + ;
}
效果图
全部代码
编辑一份.html文件，将代码拷入，作为网页打开即可使用。
<!DOCTYPE html>
<html> <head>
<meta charset="UTF-8">
<title>Lexical_Analysis</title>
<link href="https://fonts.googleapis.com/css?family=Noto+Serif+SC" rel="stylesheet">
<style>
main {
/*对子元素开启弹性布局*/
display: flex;
/*弹性元素在必要的时候换行*/
flex-wrap: wrap;
/*将弹性元素居中*/
justify-content: center;
} textarea,
button {
font-family: 'Noto Serif SC', STFangSong, serif;
font-size: 17px;
}
</style>
</head> <body>
<main>
<textarea name="input" rows="20" cols="40"></textarea>
<textarea name="output" rows="20" cols="40"></textarea>
<button name="compile">Lexical Analysis</button>
</main>s <script>
let inputBox = document.querySelector("textarea[name=input]");
let outputBox = document.querySelector("textarea[name=output]");
let btnCompile = document.querySelector("button[name=compile]");
btnCompile.addEventListener("click", event => {
let inputCode = inputBox.value;
outputBox.value = JSON.stringify(Lexical_Analysis(inputCode));
});
/*
* 规则:
识别保留字：if、int、for、while、do、return、break、continue；
单词种别码为1。
其他的都识别为标识符；单词种别码为2。
常数为无符号整形数；单词种别码为3。
运算符包括：+、-、*、/、=、>、<、>=、<=、!= ；单词种别码为4。
分隔符包括：,、;、{、}、(、)； 单词种别码为5。
*/
const reservedWords = ['if', 'int', 'for', 'while', 'do', 'return', 'break', 'continue'];
const operators = ['+', '-', '*', '/', '=', '<', '>', '!', '>=', '<=', '!='];
const separators = [',', ';', '{', '}', '(', ')']; function Lexical_Analysis(str) {
/**
* current用于标识当前字符位置,
* str[cur]即为当前字符
*/
let cur = 0;
/**
* tokens存储词法分析的最终结果
*/
let tokens = []; while(cur < str.length) { if(/\s/.test(str[cur])) { // 跳过空格
cur++;
} else if(/[a-z]/i.test(str[cur])) { // 读单词
debugger;
let word = "" + str[cur++];
// 测试下一位字符,如果不是字母直接进入下一次循环(此时cur已经右移)
// 如果是则继续读字母,并将cur向右移动
while(cur < str.length && /[a-z]/i.test(str[cur])) {
// cur < str.length防止越界
word += str[cur++];
}
if(reservedWords.includes(word)) {
tokens.push({
type: 1,
value: word,
}); // 存储保留字(关键字)
} else {
tokens.push({
type: 2,
value: word,
}); // 存储普通单词
}
} else if(separators.includes(str[cur])) {
tokens.push({
type: 5,
value: str[cur++],
}); // 存储分隔符并将cur向右移动
} else if(operators.includes(str[cur])) {
let operator = "" + str[cur++];
if(['>', '<', '!'].includes(operator)) {
// 如果下一个字符是=就添加到operator并再次向右移动cur
if(str[cur] = '=') {
operator += str[cur++];
}
}
tokens.push({
type: 4,
value: operator,
}); // 存储运算符
} else if(/[0-9]/.test(str[cur])) {
let val = "" + str[cur++];
// cur < str.length防止越界
while(cur < str.length && /[0-9]/.test(str[cur])) {
val += str[cur++];
}
tokens.push({
type: 3,
value: val,
}); // 存储整数数字
} else {
return "包含非法字符：" + str[cur];
} }
return tokens;
}
</script>
</body>
</html>
附件，龙书2.6节练习：
<!DOCTYPE html>
<html> <head>
<meta charset="UTF-8">
<title></title>
<link href="https://fonts.googleapis.com/css?family=Noto+Serif+SC" rel="stylesheet">
<style>
main {
/*对子元素开启弹性布局*/
display: flex;
/*弹性元素在必要的时候换行*/
flex-wrap: wrap;
/*将弹性元素居中*/
justify-content: center;
} textarea,
button {
font-family: 'Noto Serif SC', STFangSong, serif;
font-size: 17px;
}
</style>
</head> <body>
<main>
<textarea name="input" rows="20" cols="40"></textarea>
<textarea name="output" rows="20" cols="40"></textarea>
<button name="execute">Execute</button>
</main> <script>
let inputBox = document.querySelector("textarea[name=input]");
let outputBox = document.querySelector("textarea[name=output]");
let btnExecute = document.querySelector("button[name=execute]"); btnExecute.addEventListener("click", event => {
let tokens = tokenizer(inputBox.value);
console.log(tokens);
}); function tokenizer(input) {
let s = input;
let cur = 0;
let peek = ' ';
let line = 1;
let words = new Map(); let readChar = () => s[cur++];
let undo = () => cur--;
let scan = () => { // 每次scan返回一个Token
// 略过空格,上次设置的peek值并不会被清空
for (;; peek = readChar()) {
if (peek == undefined) {
return null; // 读完了
} else if (peek == ' ' || peek == '\t') {
continue; // 略过空格和Tab
} else if (peek == '\n') {
line++; // 记录当前行
} else {
break;
}
} // 略过注释
if ('/' == peek) {
peek = readChar();
if ('/' == peek) {
// 注释类型1
peek = readChar();
for (;; peek = readChar()) {
if (peek == '\n') {
break; // 正常退出
} else if (peek == undefined) {
return null; // 读完了,正常退出
}
}
} else if ('*' == peek) {
peek = readChar();
// 注释类型2
let lastAsterisk = false;
for (;; peek = readChar()) {
if (peek == undefined) {
console.log("注释语法错误01");
return null; // 语法错误
} else if (peek == '\n') {
lastAsterisk = false;
line++; // 记录当前行
} else if (peek == '*') {
lastAsterisk = true;
} else if (lastAsterisk && peek == '/') {
peek = readChar();
break; // 正常退出
} else {
lastAsterisk = false;
}
}
} else {
// 语法错误
console.log("注释语法错误02");
return null;
}
} // 略过空格,上次设置的peek值并不会被清空
for (;; peek = readChar()) {
if (peek == undefined) {
return null; // 读完了
} else if (peek == ' ' || peek == '\t') {
continue; // 略过空格和Tab
} else if (peek == '\n') {
line++; // 记录当前行
} else {
break;
}
} if (/[0-9.]/.test(peek)) {
let temp = peek;
let hasPoint = false;
if (peek == '.') hasPoint = true;
while (/[0-9.]/.test(peek = readChar())) {
if (peek == '.' && hasPoint) {
console.log("语法错误3，包含多个小数点");
return null;
} else if (peek == '.') {
hasPoint = true;
temp += peek;
} else {
temp += peek;
}
}
return {
tag: 'NUM',
value: Number(temp),
};
} if (/[a-zA-z]/.test(peek)) {
let temp = peek;
while ((peek = readChar()) && /[a-zA-z]/.test(peek)) {
// 经测试,null和undefined都能通过/\w/以及/[a-zA-z]/,并可以转化为字面字符串
temp += peek;
}
let w = words.get(temp);
if (w != undefined) {
return w;
} else {
w = {
tag: 'ID',
lexeme: temp,
};
words.set(temp, w);
return w;
}
} if (/[><=!]/.test(peek)) {
let first = peek;
peek = readChar();
if (peek == '=') {
peek = readChar(); // 避免重复处理
return {
tag: '逻辑运算符',
value: first + '=',
};
} else if (first != '=') {
return {
tag: '逻辑运算符',
value: first,
};
} else { // 单个=的情况,回溯
undo();
peek = first;
}
} let res = {
tag: peek,
};
peek = ' ';
return res;
}; let tokens = [];
let token;
while (token = scan()) {
tokens.push(token);
}
return tokens;
}
</script>
</body> </html>