Rust nom

Welcome to Nominomicon; a guide to using the Nom parser for great good. Rust nom guide will give you an introduction to the theory and practice of using Nom. By combining parsers with combinators, you can build complex parsers up from simpler ones, rust nom.

This tutorial is a guide to parsing with nom. It covers the basics of parsing and how to use nom to parse a string into a data structure. We will cover a variety of different examples ranging from parsing simple CSS like syntax to a full blown Markdown parser. If you would like to get involved in an open source project and like Rust crates, we welcome your contributions to the r3bl-open-core repo. For more information on general Rust type system design functional approach rather than object oriented , please take a look at this paper by Will Crichton demonstrating Typed Design Patterns with Rust. This tutorial takes a hands on approach to learning nom. However, the resources listed below are very useful for learning nom.

Rust nom

Its goal is to provide tools to build safe parsers without compromising the speed or memory consumption. To that end, it uses extensively Rust's strong typing and memory safety to produce fast and correct parsers, and provides functions, macros and traits to abstract most of the error prone plumbing. Hexadecimal color parser:. Compared to the usual handwritten C parsers, nom parsers are just as fast, free from buffer overflow vulnerabilities, and handle common patterns for you:. While nom was made for binary format at first, it soon grew to work just as well with text formats. From line based formats like CSV, to more complex, nested formats such as JSON, nom can manage it, and provides you with useful tools:. While programming language parsers are usually written manually for more flexibility and performance, nom can be and has been successfully used as a prototyping parser for a language. No need for separate tokenizing, lexing and parsing phases: nom can automatically handle whitespace parsing, and construct an AST in place. While a lot of formats and the code handling them assume that they can fit the complete data in memory, there are formats for which we only get a part of the data at once, like network formats, or huge files. Whether your data comes entirely or in chunks, the result should be the same. Parser combinators are an approach to parsers that is very different from software like lex and yacc. Instead of writing the grammar in a separate file and generating the corresponding code, you use very small functions with very specific purpose, like "take 5 bytes", or "recognize the word 'HTTP'", and assemble them in meaningful patterns like "recognize 'HTTP', then a space, then a version". The resulting code is small, and looks like the grammar you would have written with other parser approaches. Some benchmarks are available on GitHub.

The match values are combined into a single value, using a binary operator. From line based formats like CSV, to more complex, rust nom, nested formats such as JSON, nom can manage it, and provides you with useful tools:.

Nom , documented here is a parser library for Rust which is well worth the initial time investment. Likewise, for configuration files use dedicated parsers like ini or toml. But if the text is not regular, or some made-up format, then you need to scan that text without writing a lot of tedious string-processing code. The suggested go-to is often regex , but regexes can be frustratingly opaque when sufficiently involved. Nom provides a way to parse text which is just as powerful and can be built up by combining simpler parsers. If you ever had the itch to write your own programming language, Nom is a good place for you start on that hard road to obscurity.

Parser combinators are higher-order functions that can accept several parsers as input and return a new parser as its output. This approach enables you to build parsers for simple tasks, such as parsing a certain string or a number, and compose them using combinator functions into a whole recursive descent parser. Benefits of combinatory parsing include testability, maintainability, and readability; each moving part is rather small and self-isolated, making the whole parser a composition of modular components. Yup, all we need is the nom library in the latest version 6. The fields are arranged according to the order in which they occur in a regular URI. First, we have the scheme. Next comes the authority part, which consists of a username and an optional password and is, in general, fully optional. The host can be either an IP in our case, only an IPv4 , or a host string, such as example.

Rust nom

Its goal is to provide tools to build safe parsers without compromising the speed or memory consumption. To that end, it uses extensively Rust's strong typing and memory safety to produce fast and correct parsers, and provides functions, macros and traits to abstract most of the error prone plumbing. Hexadecimal color parser:. Compared to the usual handwritten C parsers, nom parsers are just as fast, free from buffer overflow vulnerabilities, and handle common patterns for you:.

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Parser combinators are an approach to parsers that is very different from software like lex and yacc. There are lots of tests that you can follow along to understand what the code is doing. Nom knows that "bye" may be followed by a name and wants us to give it more data. Here I'll throw caution to the winds and throw away the error:! Latest commit. But it gets better. This is the great power of Nom, and it's why it's called a "parser combinator library". If you are upgrading to nom 5. History 2, Commits. Parsing Arithmetic Expressions With the necessary background established, we can do simple arithmetic expressions. And then we can parse and convert floating point numbers. This signature is the pattern that we will end up using to figure out how to chain combinators together.

I've been working on my new Rust side-project for several months now , and I've got some learnings to share. The project is called pq - it's a command-line tool to parse and query log files as time series.

The opt combinator makes a parser optional. A streaming parser assumes that we might not have all of the input data. Basics 2. Going further: Read the guides , check out the recipes! By combining parsers with combinators, you can build complex parsers up from simpler ones. Streaming formats. Note that you can use whitespace here to make the parser function easier to read:. Structs, Enums and Matching 3. A parser in nom is a function which, for an input type I , an output type O and an optional error type E , will have the following signature:. This is how serde does it, albeit there it is not public. Parsers returning any unparsed text, and being able to indicate that they don't have enough input characters to decide, is very useful for stream parsing.