bea4dev/bnf_rules

LR(1) parser generator

bnf_rules!

LR(1) parser generator

Generate LR(1) parser at compilation time.

use bnf_rules::bnf_rules_macro::bnf_rules;
use bnf_rules::bnf_rules_parser::{*};
use bnf_rules::bnf_rules_parser::lexer::{*};
use bnf_rules::bnf_rules_parser::parser::{*};

// Grammer
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());

}

Usage

bnf_rules = { git = "https://github.com/bea4dev/bnf_rules" }

Extended BNF

Form	Semantic
source	An entire input source.
ident	A non-terminal symbol named "ident".
"something"	A terminal symbol for text.
fn (function_name)	A custom tokenizer with user function.1
{ pattern }	Zero or more repetitions of "pattern".
[ pattern ]	"pattern" or null.
pattern1 | pattern2	"pattern1" or "pattern2".
( patterns )	A group of patterns.

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

Footnotes

1. Generic parameters are also available. ↩