帮助理解术语 In general, there is a set of strings in the input for which the same token is produced as output. This set of strings is described by a rule called a pattern associated with the token. The pattern is said to match each string in the set a lexeme is a sequence of characters in the source program that is matched by the pattern for a token g Const pi=3.14159;中的 p是 token“ identifier 的 lexeme,其 pattern为 letter followed by letters and/or digit帮助理解术语 In general，there is a set of strings in the input for which the same token is produced as output. This set of strings is described by a rule called a pattern associated with the token. The pattern is said to match each string in the set. A lexeme is a sequence of characters in the source program that is matched by the pattern for a token. e.g. – Const pi=3.14159；中的pi是token “identifier” 的lexeme，其pattern为letter followed by letters and/or digit