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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