Action code

Action code is normal Rust code with the addition of the following special variables:

• $1 ... $n refer to the respective symbol in the production, numbered from 1 (i.e. $1 refers to the first symbol in the production). If the symbol references a rule R then an instance of R's type will be stored in the $i variable; if the symbol references a lexeme then an Option<Lexeme> instance is returned.

• $lexer allows access to the lexer and its various functions. The most commonly used of these is the lexeme_str function, which allows us to turn Lexemes into &strs representing the corresponding portion of the user's input.

• $span is a (start, end) tuple (with both elements of type usize) which captures how much of the user's input the current production matched. This can be useful when storing debugging information. Note that this variable is not enabled by default: use CTParserBuilder::span_var(true) to enable it.