PHP怎么实现词法分析与自定义语言

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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。

", "<", "!", "(", ")", "{", "}", ",", ";"    ];    // 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$code = << 3){    地址=1;}否则{    地址="艾欧尼亚"}说话 = ("我"+"爱")+"你";返回 姓名+年龄;EOF;$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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