baitcenter / rust-peg

Parsing Expression Grammar (PEG) parser generator for Rust

Parsing Expression Grammars in Rust

Documentation | Release Notes

rust-peg is a simple yet flexible parser generator based on the Parsing Expression Grammar formalism. It provides a Rust macro that builds a recursive descent parser from a concise definition of the grammar.

Features

• Parse input from &str, &[u8], &[T] or custom types implementing traits
• Customizable reporting of parse errors
• Rules can accept arguments to create reusable rule templates
• Precedence climbing for prefix/postfix/infix expressions
• Helpful rustc error messages for errors in the grammar definition or the Rust code embedded within it
• Rule-level tracing to debug grammars

Example

use peg::parser;

parser!{
  grammar list_parser() for str {
    rule number() -> u32
      = n:$(['0'..='9']+) { n.parse().unwrap() }
    
    pub rule list() -> Vec<u32>
      = "[" l:number() ** "," "]" { l }
  }
}

pub fn main() {
    assert_eq!(list_parser::list("[1,1,2,3,5,8]"), Ok(vec![1, 1, 2, 3, 5, 8]));
}

See the tests for more examples
Grammar rule syntax reference in rustdoc

Comparison with similar parser generators

crate	parser type	action code	integration	input type	precedence climbing	parameterizd rules	streaming input
peg	PEG	in grammar	proc macro (block)	&str, &[T], custom	Yes	Yes	No
pest	PEG	external	proc macro (file)	&str	Yes	No	No
nom	combinators	in source	library	&[u8], custom	No	Yes	Yes
lalrpop	LR(1)	in grammar	build script	&str	No	Yes	No