Rust nom

Welcome to Nominomicon; a guide to using the Nom parser for great good.

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.

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.

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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.

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:.

Rust nom

There are a few guides with more details about the design of nom macros , how to write parsers , or the error management system. Looking for a specific combinator? Read the "choose a combinator" guide. If you are upgrading to nom 5. 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 syntax and generating the corresponding code, you use very small functions with very specific purposes, 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. It defines a function named parens which will recognize a sequence of the character , the longest byte array not containing , then the character , and will return the byte array in the middle.

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Before we set off, it's important to list some caveats: This guide is for Nom7. 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. Naturally, the second value of the tuple becomes an Option. We're going to need floating-point asserts here, and there's a crate for that. We're not interested in that tag's value it can only be a comma but we assign the two float values to temporary values which are used to build a struct. Object-Oriented Programming 9. Structs, Enums and Matching 3. Go to file. Creates a parse error from a nom::ErrorKind and the position in the input. Parser combinators are an approach to parsers that is very different from software like lex and yacc. For more complicated expressions, capturing the results of all the parsers leads to rather untidy types! 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. They hold different variants of the same combinators.

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.

Releases 90 tags. By defining a little helper macro, we get some passing tests. Want to create a new parser using nom? A list of not yet implemented formats is available here. And the second means that Nom can be used for any data format, not just text. Let's continue the greeting example and imagine that a greeting consists of "hi" or "bye", plus a name. Alternatives and Composition 4. Please note how it's possible to build up complicated parsers step by step, testing each part in isolation first. And indeed we get back the matching value. After the really complicated walk through above, we could have just written the entire thing concisely like so:. Structs, Enums and Matching 3. 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. Creates a parse error from a nom::ErrorKind and the position in the input. Its goal is to provide tools to build safe parsers without compromising the speed or memory consumption.