# Logos  [](https://crates.io/crates/logos2) [](https://docs.rs/logos2) [](https://crates.io/crates/logos2) _Create ridiculously fast Lexers._ **Logos** has two goals: + To make it easy to create a Lexer, so you can focus on more complex problems. + To make the generated Lexer faster than anything you'd write by hand. To achieve those, **Logos**: + Combines all token definitions into a single [deterministic state machine](https://en.wikipedia.org/wiki/Deterministic_finite_automaton). + Optimizes branches into [lookup tables](https://en.wikipedia.org/wiki/Lookup_table) or [jump tables](https://en.wikipedia.org/wiki/Branch_table). + Prevents [backtracking](https://en.wikipedia.org/wiki/ReDoS) inside token definitions. + [Unwinds loops](https://en.wikipedia.org/wiki/Loop_unrolling), and batches reads to minimize bounds checking. + Does all of that heavy lifting at compile time. ## Example ```rust use logos::Logos; #[derive(Logos, Debug, PartialEq)] #[logos(skip r"[ \t\n\f]+")] // Ignore this regex pattern between tokens enum Token { // Tokens can be literal strings, of any length. #[token("fast")] Fast, #[token(".")] Period, // Or regular expressions. #[regex("[a-zA-Z]+")] Text, } fn main() { let mut lex = Token::lexer("Create ridiculously fast Lexers."); assert_eq!(lex.next(), Some(Ok(Token::Text))); assert_eq!(lex.span(), 0..6); assert_eq!(lex.slice(), "Create"); assert_eq!(lex.next(), Some(Ok(Token::Text))); assert_eq!(lex.span(), 7..19); assert_eq!(lex.slice(), "ridiculously"); assert_eq!(lex.next(), Some(Ok(Token::Fast))); assert_eq!(lex.span(), 20..24); assert_eq!(lex.slice(), "fast"); assert_eq!(lex.next(), Some(Ok(Token::Text))); assert_eq!(lex.slice(), "Lexers"); assert_eq!(lex.span(), 25..31); assert_eq!(lex.next(), Some(Ok(Token::Period))); assert_eq!(lex.span(), 31..32); assert_eq!(lex.slice(), "."); assert_eq!(lex.next(), None); } ``` For more examples and documentation, please refer to the [Logos handbook](https://maciejhirsz.github.io/logos/) or the [crate documentation](https://docs.rs/logos2/latest/logos/). ## How fast? Ridiculously fast! ```norust test identifiers ... bench: 647 ns/iter (+/- 27) = 1204 MB/s test keywords_operators_and_punctators ... bench: 2,054 ns/iter (+/- 78) = 1037 MB/s test strings ... bench: 553 ns/iter (+/- 34) = 1575 MB/s ``` ## Acknowledgements + [Pedrors](https://pedrors.pt/) for the **Logos** logo. ## Thank you **Logos** is very much a labor of love. If you find it useful, consider [getting me some coffee](https://github.com/sponsors/maciejhirsz). ☕ If you'd like to contribute to Logos, then consider reading the [Contributing guide](https://maciejhirsz.github.io/logos/contributing). ## License This code is distributed under the terms of both the MIT license and the Apache License (Version 2.0), choose whatever works for you. See [LICENSE-APACHE](LICENSE-APACHE) and [LICENSE-MIT](LICENSE-MIT) for details.