Rust nom

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

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. There are some excellent tutorials for learning Nom, but I want to start at the hello-world level to build some initial familiarity.

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. Want to create a new parser using nom?

There are still a lot of mistakes one can make.

There are a few guides with more details about how to write parsers , or the error management system. You can also check out the recipes module that contains examples of common patterns. Looking for a specific combinator? If you are upgrading to nom 5. Parser combinators are an approach to parsers that is very different from software like lex and yacc. The resulting code is small, and looks like the grammar you would have written with other parser approaches.

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. There are some excellent tutorials for learning Nom, but I want to start at the hello-world level to build some initial familiarity. The basic things you need to know - first, Nom is macros all the way down, and second, Nom prefers to work with byte slices, not strings. The first means that you have to be especially careful to get Nom expressions right, because the error messages are not going to be friendly.

Rust nom

It conjures visions of obscure grammars fed into arcane tools to generate thousands of lines of unreadable code. Parser combinator libraries such as nom present a library of small functions that each do one thing, and then allow you to put them together to create a full parser. Some expressions, such as Bold , contain other expressions. Our first parser, word , just gets a single word.

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We can write a generic dump function that handles any return value that can be debug-printed. And then we can parse and convert floating point numbers. There are a few guides with more details about how to write parsers , or the error management system. Now, further imagine that the greeter is perhaps a little shy or doesn't know anybody's name: let us make the name optional. This module contains a parser that parses a hex color string into a [Color] struct. Regular expressions are certainly more compact!. You can write small functions that parse a specific part of your input, and then combine them to build a parser that parses the whole input. Up to now, we've had to capture every expression, or just grab all matching bytes with recognize! Its goal is to provide tools to build safe parsers without compromising the speed or memory consumption. And the stripped release build executable of the Nom example is about 0. Nom knows that "bye" may be followed by a name and wants us to give it more data. See also the rest of the documentation here.

There are a few guides with more details about how to write parsers , or the error management system.

Releases 90 tags. With the necessary background established, we can do simple arithmetic expressions. This is the great power of Nom, and it's why it's called a "parser combinator library". It makes a great starting point to study how a relatively complex parser is written. The Err enum indicates the parser was not successful. Errors are a key part of it being able to apply a variety of different parsers to the same input. Basics 2. Latest commit History 2, Commits. Structs, Enums and Matching 3. Notice that it was straightforward to combine an existing parser for greetings with a parser that picks up names, and then it was easy to make that name optional. The resulting code is small, and looks like the grammar you would have written with other parser approaches. Documentation nom is a huge topic. This tutorial is a guide to parsing with nom. Custom Outputs from Functions 5.