在编译时生成 LR(1) 解析器。

use bnf_rules::bnf_rules_macro::bnf_rules;

// Grammar
bnf_rules!(
    source   ::= expr
    expr     ::= factor { "+" factor }
    factor   ::= "-" primary | primary
    primary  ::= "(" expr ")" | number
    number   ::= fn (number_tokenizer) // custom tokenizer with function
);

/// Custom tokenizer for numeric literal
fn number_tokenizer(source: &Vec<char>, mut current_position: usize) -> usize {
    let mut iteration_count = 0;
    loop {
        let current_char = match source.get(current_position) {
            Some(ch) => ch.clone(),
            _ => break
        };
        if !current_char.is_numeric() {
            break;
        }
        iteration_count += 1;
        current_position += 1;
    }
    return iteration_count; // 0 means 'rejected', other means 'accepted' and 'length of token'.
}

pub fn parse() {

    // A function named "parse_source" is automatically generated.
    let ast_node: Result<ASTNode, ParseError> = parse_source("(100 + 200) + -100");
    dbg!(ast_node.unwrap());

}

用法

bnf_rules = "0.1.4"

扩展 BNF

[^1]: 也可用泛型参数。

示例 1: https://github.com/bea4dev/bnf_rules/blob/master/src/lib.rs

示例 2: https://github.com/bea4dev/catla/blob/master/catla_parser/src/grammar.rs