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diff --git a/_README.md b/_README.md new file mode 100644 index 0000000..8e55f29 --- /dev/null +++ b/_README.md @@ -0,0 +1,169 @@ +<p align="center"> + <img src="https://raw.github.com/pest-parser/pest/master/pest-logo.svg?sanitize=true" width="80%"/> +</p> + +# pest. The Elegant Parser + +[](https://gitter.im/dragostis/pest?utm_source=badge&utm_medium=badge&utm_campaign=pr-badge&utm_content=badge) +[](https://pest-parser.github.io/book) +[](https://docs.rs/pest) + +[](https://travis-ci.org/pest-parser/pest) +[](https://codecov.io/gh/pest-parser/pest) +[](https://app.fuzzit.dev/orgs/pest-parser/dashboard) +[](https://crates.io/crates/pest) +[](https://crates.io/crates/pest) + +pest is a general purpose parser written in Rust with a focus on accessibility, +correctness, and performance. It uses parsing expression grammars +(or [PEG]) as input, which are similar in spirit to regular expressions, but +which offer the enhanced expressivity needed to parse complex languages. + +[PEG]: https://en.wikipedia.org/wiki/Parsing_expression_grammar + +## Getting started + +The recommended way to start parsing with pest is to read the official [book]. + +Other helpful resources: + +* API reference on [docs.rs] +* play with grammars and share them on our [fiddle] +* leave feedback, ask questions, or greet us on [Gitter] + +[book]: https://pest-parser.github.io/book +[docs.rs]: https://docs.rs/pest +[fiddle]: https://pest-parser.github.io/#editor +[Gitter]: https://gitter.im/dragostis/pest + +## Example + +The following is an example of a grammar for a list of alpha-numeric identifiers +where the first identifier does not start with a digit: + +```rust +alpha = { 'a'..'z' | 'A'..'Z' } +digit = { '0'..'9' } + +ident = { (alpha | digit)+ } + +ident_list = _{ !digit ~ ident ~ (" " ~ ident)+ } + // ^ + // ident_list rule is silent which means it produces no tokens +``` + +Grammars are saved in separate .pest files which are never mixed with procedural +code. This results in an always up-to-date formalization of a language that is +easy to read and maintain. + +## Meaningful error reporting + +Based on the grammar definition, the parser also includes automatic error +reporting. For the example above, the input `"123"` will result in: + +``` +thread 'main' panicked at ' --> 1:1 + | +1 | 123 + | ^--- + | + = unexpected digit', src/main.rs:12 +``` +while `"ab *"` will result in: +``` +thread 'main' panicked at ' --> 1:1 + | +1 | ab * + | ^--- + | + = expected ident', src/main.rs:12 +``` + +## Pairs API + +The grammar can be used to derive a `Parser` implementation automatically. +Parsing returns an iterator of nested token pairs: + +```rust +extern crate pest; +#[macro_use] +extern crate pest_derive; + +use pest::Parser; + +#[derive(Parser)] +#[grammar = "ident.pest"] +struct IdentParser; + +fn main() { + let pairs = IdentParser::parse(Rule::ident_list, "a1 b2").unwrap_or_else(|e| panic!("{}", e)); + + // Because ident_list is silent, the iterator will contain idents + for pair in pairs { + // A pair is a combination of the rule which matched and a span of input + println!("Rule: {:?}", pair.as_rule()); + println!("Span: {:?}", pair.as_span()); + println!("Text: {}", pair.as_str()); + + // A pair can be converted to an iterator of the tokens which make it up: + for inner_pair in pair.into_inner() { + match inner_pair.as_rule() { + Rule::alpha => println!("Letter: {}", inner_pair.as_str()), + Rule::digit => println!("Digit: {}", inner_pair.as_str()), + _ => unreachable!() + }; + } + } +} +``` + +This produces the following output: +``` +Rule: ident +Span: Span { start: 0, end: 2 } +Text: a1 +Letter: a +Digit: 1 +Rule: ident +Span: Span { start: 3, end: 5 } +Text: b2 +Letter: b +Digit: 2 +``` + +## Other features + +* Precedence climbing +* Input handling +* Custom errors +* Runs on stable Rust + +## Projects using pest + +* [pest_meta](https://github.com/pest-parser/pest/blob/master/meta/src/grammar.pest) (bootstrapped) +* [AshPaper](https://github.com/shnewto/ashpaper) +* [brain](https://github.com/brain-lang/brain) +* [Chelone](https://github.com/Aaronepower/chelone) +* [comrak](https://github.com/kivikakk/comrak) +* [elastic-rs](https://github.com/cch123/elastic-rs) +* [graphql-parser](https://github.com/Keats/graphql-parser) +* [handlebars-rust](https://github.com/sunng87/handlebars-rust) +* [hexdino](https://github.com/Luz/hexdino) +* [Huia](https://gitlab.com/jimsy/huia/) +* [jql](https://github.com/yamafaktory/jql) +* [json5-rs](https://github.com/callum-oakley/json5-rs) +* [mt940](https://github.com/svenstaro/mt940-rs) +* [py_literal](https://github.com/jturner314/py_literal) +* [rouler](https://github.com/jarcane/rouler) +* [RuSh](https://github.com/lwandrebeck/RuSh) +* [rs_pbrt](https://github.com/wahn/rs_pbrt) +* [stache](https://github.com/dgraham/stache) +* [tera](https://github.com/Keats/tera) +* [ui_gen](https://github.com/emoon/ui_gen) +* [ukhasnet-parser](https://github.com/adamgreig/ukhasnet-parser) +* [ZoKrates](https://github.com/ZoKrates/ZoKrates) + +## Special thanks + +A special round of applause goes to prof. Marius Minea for his guidance and all +pest contributors, some of which being none other than my friends. |