yacc可以识别出记号的模式；例如，如上面例子中所示，它可以识别出一个表达式可能由一个值、一个加号或者减号以及另一个值构成。
Yacc can recognize patterns of tokens; for instance, as in the example above, it can recognize that an expression can consist of a value, either a plus or minus sign, and another value.
TOKEN 语句包含类似 regex 的表达式，该表达式描述了整数记号看起来象什么。
The TOKEN statement contains a regex-like expression that describes what integer tokens look like.
计量符可以在Spark记号赋予器(tokenizer)的正则表达式中使用，并可以用解析表达式语法中的递归来进行模拟。
Quantifiers can be used within the regular expressions of the Spark tokenizer, and can be simulated by recursion in parse expression grammars.
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