java - EBNF 到 JavaCC 词法分析器

Question

如何将::= [A-Za-z] 转换为 JavaCC？

我做了什么:

TOKEN :
{
  < LETTER : (["A"-"Z"])>
}

但我不知道如何做较小的字母部分

Answer 1

像这样:

TOKEN :
{
  < LETTER : (["A"-"Z", "a"-"z"])>
}

Reference :

A character list describes a set of characters. A legal match for a character list is any character in this set. A character list is a list of character descriptors separated by commas within square brackets. Each character descriptor describes a single character or a range of characters (see character descriptor below), and this is added to the set of characters of the character list. If the character list is prefixed by the "~" symbol, the set of characters it represents is any UNICODE character not in the specified set.

请注意规则:

TOKEN :
{
  < LETTER : (["A"-"Z", "a"-"z"])>
}

相当于:

TOKEN :
{
  < LETTER : ["A"-"Z", "a"-"z"]>
}

两者都匹配单个字母。如果您想重复该类，则需要括号并附加一个 + 量词:

TOKEN :
{
  < LETTERS : (["A"-"Z", "a"-"z"])+ >
}