之前项目有一个需求，业务人员使用中文编写一些自定义公式，然后需要我们后台执行将结果返回到界面上，于是就基于有限状态机写了这个词法分析器，比较简单，希望能够抛砖引玉。
一、分析需求
输入中文公式，返回结果，比如：
现有薪资=10000;
个税起点=3000;
当前年份=2021;
如果(当前年份=2022){
个税起点=5000;
}
返回 (现有薪资-个税起点) * 0.2;二、实现需求
最初的想法是使用字符串替换的方式，将中文关键字替换成php的关键字，然后调用eval执行，这样确实也是可以的，但是总觉得不是很美丽，并且不能实现动态解析。就想着自己实现一个简单的词法分析，然后结合ast将词法转换成php代码执行，岂不快哉。当前版本没有用到抽象语法树来生成代码，全部使用字符串拼接。【推荐学习：PHP教程】
<?php
/**
* Class Lexer
* @package Sett\OaLang
* 词法分析器
*/
class Lexer {
// 内置关键字集合
public $keywordList = [];
// 内置操作符集合
public $operatorList = [
+, -, *, /, =, >, <, !, (, ), {, }, ,, ;
];
// 源代码
private $input;
// 当前的字符
private $currChar;
// 当前字符位置
private $currCharPos = 0;
// 结束符
private $eof = eof;
// 当前编码
private $currEncode = UTF-8;
// 内置关键字
public const VAR = variable;
public const STR = string;
public const KW = keyword;
public const OPR = operator;
public const INT = integer;
public const NIL = null;
/**
* Lexer constructor.
* @param string $input
*/
public function __construct(string $input) {
$this->input = $input;
$this->currChar = mb_substr($this->input, $this->currCharPos, 1);
}
/**
* @param array $keywordList
*/
public function setKeywordList($keywordList) {
$this->keywordList = $keywordList;
}
/**
* @return array
* @throws Exception
*/
public function parseInput() {
if ($this->input == ) {
throw new Exception(code can not be empty);
}
$tokens = [];
do {
$token = $this->nextToken();
if ($token[type] != eof) {
$tokens[] = $token;
}
if ($token[type] == self::KW) {
$tokens[] = $this->makeToken(self::NIL, );
}
} while ($token[type] != eof);
return $tokens;
}
/**
* @return array
*/
public function nextToken() {
$this->skipBlankChar();
$this->currChar == && $this->currChar = $this->eof;
if ($this->isCnLetter()) {
$word = $this->matchUntilNextCharIsNotCn();
if ($this->isKeyword($word)) {
$this->currCharPos -= 1;
return $this->currToken(static::KW, $word);
}
// 不是关键字的全部归为变量
return $this->makeToken(static::VAR, $word);
}
// 如果是操作符
if ($this->isOperator()) {
return $this->currToken(static::OPR, $this->currChar);
}
// 如果是数字
if ($this->isNumber()) {
return $this->currToken(static::INT, $this->currChar);
}
// 如果是字符串
if ($str = $this->isStr()) {
return $this->currToken(static::STR, $str);
}
// 如果是变量
if ($this->isVar()) {
$word = $this->matchVar();
if ($this->isKeyword($word)) {
return $this->currToken(static::KW, $word);
}
return $this->makeToken(static::VAR, $word);
}
if ($this->currChar == $this->eof) {
return $this->currToken('eof', $this->currChar);
}
return $this->currToken(static::VAR, $this->currChar);
}
/**
* @param string $input
* @return string
*/
private function matchVar(string $input = ) {
$word = $input ?: '';
while ($this->isVar()) {
$word .= $this->currChar;
$this->nextChar();
}
return $word;
}
/**
* @return bool
* 是否为普通变量
*/
private function isVar() {
return $this->isCnLetter() || $this->isEnLetter();
}
/**
* 跳过空白字符
*/
private function skipBlankChar() {
while (ord($this->currChar) == 10 ||
ord($this->currChar) == 13 ||
ord($this->currChar) == 32) {
$this->nextChar();
}
}
/**
* @param string $type
* @param $word
* @return array
* 记录当前token和下一个字符
*/
private function currToken(string $type, $word) {
$token = $this->makeToken($type, $word);
$this->nextChar();
return $token;
}
/**
* @param string $type
* @param string $char
* @return array
*/
private function makeToken(string $type, string $char) {
return [type => $type, char => $char, pos => $this->currCharPos];
}
/**
* @return bool
* 判断是否是英文字符
*/
private function isEnLetter() {
if ($this->currChar == || $this->currChar == $this->eof) {
return false;
}
$ord = mb_ord($this->currChar, $this->currEncode);
if ($ord > ord('a') && $ord < ord('z')) {
return true;
}
return false;
}
/**
* @return false|int
* 是否中文字符
*/
private function isCnLetter() {
return preg_match(/^[\x{4e00}-\x{9fa5}]+$/u, $this->currChar);
}
/**
* @return bool
* 是否为数字
*/
private function isNumber() {
return is_numeric($this->currChar);
}
/**
* @return bool
* 是否是字符串
*/
private function isStr() {
return $this->matchCompleteStr();
}
/**
* @return string
* 匹配完整字符串
*/
private function matchCompleteStr() {
$char = ;
if ($this->currChar == \) {
$this->nextChar();
while ($this->currChar != \) {
if ($this->currChar != \) {
$char .= $this->currChar;
}
$this->nextChar();
}
return $char;
}
return $char;
}
/**
* @return bool
* 是否是操作符
*/
private function isOperator() {
return in_array($this->currChar, $this->operatorList);
}
/**
* @return string
* 匹配中文字符
*/
private function matchUntilNextCharIsNotCn() {
$char = ;
while ($this->isCnLetter()) {
$char .= $this->currChar;
$this->nextChar();
}
return $char;
}
/**
* @return void 获取下一个字符
* 获取下一个字符
*/
private function nextChar() {
$this->currCharPos += 1;
$this->currChar = mb_substr($this->input, $this->currCharPos, 1);
if ($this->currChar == ) {
$this->currChar = $this->eof;
}
}
/**
* @param string $input
* @return bool
* 是否是关键字
*/
private function isKeyword(string $input) {
return ($this->keywordList[$input] ?? ) != ;
}
public function convert(array $tokens) {
$code = ;
foreach ($this->lexerIterator($tokens) as $generator) {
switch ($generator[type]) {
case static::KW:
$code .= $this->keywordList[$generator[char]];
break;
case static::VAR:
$code .= sprintf($%s, $generator[char]);
break;
case static::OPR:
$code .= $this->replace($generator[char]);
break;
case static::INT:
$code .= $generator[char];
break;
case static::STR:
$code .= sprintf(\%s\, $generator[char]);
break;
default:
$code .= $generator[char];
}
}
return $code;
}
private function replace(string $char) {
return str_replace(+, ., $char);
}
/**
* @param array $tokens
* @return \Generator
*/
private function lexerIterator(array $tokens) {
foreach ($tokens as $index => $token) {
yield $token;
}
}
}三、如何使用
require __DIR__ . /vendor/autoload.php;
// 定义一段代码
$code = <<<EOF
姓名=腕豪;
问候=你好啊;
地址=(1+2) * 3;
如果(地址 > 3){
地址=1;
}否则{
地址=艾欧尼亚
}
说话 = (我+爱)+你;
返回 姓名+年龄;
EOF;
$lexer = new Lexer($code);
// 自定义你的关键字
$kwMap = [
如果 => if, 否则 => else, 返回 => return, 否则如果 => elseif
];
$lexer->setKeywordList($kwMap);
// 这里是生成的词
$tokens = $lexer->parseInput();
// 将生成的词转成php,当然你也可以尝试用php-parse转ast再转成php，这里只是简单的拼接
var_dump($lexer->convert($tokens));生成词
[{
type: variable,
char: 姓名,
pos: 2}, {
type: operator,
char: =,
pos: 2}, {
type: string,
char: 腕豪,
pos: 7}, {
type: operator,
char: ;,
pos: 8}, {
type: variable,
char: 问候,
pos: 13}, {
type: operator,
char: =,
pos: 13}, {
typ e: string,
char: 你好啊,
pos: 17}, {
type: operator,
char: ;,
pos: 18}, {
type: variable,
char: 地址,
pos: 23}, {
type: operator,
char: =,
pos: 23}, {
type: operator,
char: (,
pos: 24}, {
type: integer,
char: 1,
pos: 25}, {
type: operator,
char: +,
pos: 26}, {
type: integer,
char: 2,
pos: 27}, {
type: operator,
char: ),
pos: 28}, {
type: operator,
char: *,
pos: 30}, {
type: integer,
char: 3,
pos: 32}, {
type: operator,
char: ;,
pos: 33}, {
type: keyword,
char: 如果,
pos: 37}, {
type: nul l,
char: ,
pos: 38}, {
type: operator,
char: (,
pos: 38}, {
type: variable,
char: 地址,
pos: 41}, {
type: operator,
char: >,
pos: 42}, {
type: integer,
char: 3,
pos: 44}, {
type: operator,
char: ),
pos: 45}, {
type: operator,
char: {,
pos: 46}, {
type: variable,
char: 地址,
pos: 55}, {
type: operator,
char: =,
pos: 55}, {
type: integer,
char: 1,
pos: 56}, {
type: operator,
char: ;,
pos: 57}, {
type: operator,
char: },
pos: 60}, {
type: keyword,
char: 否则,
pos: 62}, {
type: null,
char : ,
pos: 63}, {
type: operator,
char: {,
pos: 63}, {
type: variable,
char: 地址,
pos: 72}, {
type: operator,
char: =,
pos: 72}, {
type: string,
char: 艾欧尼亚,
pos: 78}, {
type: operator,
char: ;,
pos: 79}, {
type: operator,
char: },
pos: 82}, {
type: variable,
char: 说话,
pos: 87}, {
type: operator,
char: =,
pos: 88}, {
type: operator,
char: (,
pos: 90}, {
type: string,
char: 我,
pos: 93}, {
type: operator,
char: +,
pos: 94}, {
type: string,
char: 爱,
pos: 97}, {
type: operator,
char: ),
pos: 98}, {
type: operator,
char: +,
pos: 99}, {
type: string,
char: 你,
pos: 102}, {
type: operator,
char: ;,
pos: 103}, {
type: keyword,
char: 返回,
pos: 107}, {
type: null,
char: ,
pos: 108}, {
type: variable,
char: 姓名,
pos: 111}, {
typ e: operator,
char: +,
pos: 111}, {
type: variable,
char: 年龄,
pos: 114}, {
type: operator,
char: ;,
pos: 114}]输出：
$姓名=腕豪;$问候=你好啊;$地址=(1.2)*3;if ($地址>3){$地址=1;}else {$地址=艾欧尼亚;}$说话=(我.爱).你;return $姓名.$年龄;能执行吗？当然能。还存在一些小bug，不想改了。
四、使用场景
什么，居然有人说没什么用？oa系统总有用到的时候。
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