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An implementation of parser combinators for Rust, inspired by the Haskell library Parsec. As in Parsec the parsers are LL(1) by default but they can opt-in to arbitrary lookahead using the attempt combinator.

Example

extern crate combine;
use combine::{many1, Parser, sep_by};
use combine::parser::char::{letter, space};

// Construct a parser that parses *many* (and at least *1) *letter*s
let word = many1(letter());

// Construct a parser that parses many *word*s where each word is *separated by* a (white)*space*
let mut parser = sep_by(word, space())
    // Combine can collect into any type implementing `Default + Extend` so we need to assist rustc
    // by telling it that `sep_by` should collect into a `Vec` and `many1` should collect to a `String`
    .map(|mut words: Vec<String>| words.pop());
let result = parser.parse("Pick up that word!");
// `parse` returns `Result` where `Ok` contains a tuple of the parsers output and any remaining input.
assert_eq!(result, Ok((Some("word".to_string()), "!")));

Larger examples can be found in the examples, tests and benches folders.

Tutorial

A tutorial as well as explanations on what goes on inside combine can be found in the wiki.

Translation

Japanese

Links

Documentation and examples

crates.io

Features

About

A parser combinator is, broadly speaking, a function which takes several parsers as arguments and returns a new parser, created by combining those parsers. For instance, the many parser takes one parser, p, as input and returns a new parser which applies p zero or more times. Thanks to the modularity that parser combinators gives it is possible to define parsers for a wide range of tasks without needing to implement the low level plumbing while still having the full power of Rust when you need it.

The library adheres to semantic versioning.

If you end up trying it I welcome any feedback from your experience with it. I am usually reachable within a day by opening an issue, sending an email or posting a message on Gitter.

FAQ

Why does my errors contain inscrutable positions?

Since combine aims to crate parsers with little to no overhead, streams over &str and &[T] do not carry any extra position information, but instead, they only rely on comparing the pointer of the buffer to check which Stream is further ahead than another Stream. To retrieve a better position, either call translate_position on the PointerOffset which represents the position or wrap your stream with State.

How does it compare to nom?

https://github.com/Marwes/combine/issues/73 contains discussion and links to comparisons to nom.

Parsers written in combine

Formats and protocols

Miscellaneous

Extra

There is an additional crate which has parsers to lex and parse programming languages in combine-language.

Contributing

The easiest way to contribute is to just open an issue about any problems you encounter using combine but if you are interested in adding something to the library here is a list of some of the easier things to work on to get started.