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#1065 in Procedural macros

3,312 downloads per month
Used in 5 crates (via databend-common-ast)

MIT license

31KB
588 lines

nom-rule

A procedural macro for writing nom parsers using a grammar-like syntax.

Overview

The nom-rule crate provides the rule! macro, which allows you to define nom parsers using a domain-specific language (DSL) that resembles grammar rules. This makes your parsers more readable and easier to maintain.

Features

Define parsers using a grammar-like syntax.
Integrates seamlessly with nom combinators.
Supports sequences, choices, repetitions, optional parsing, and more.

Usage

use nom_rule::rule;

// Define your match functions
fn match_text<'a>(text: &'a str) -> impl FnMut(Input<'a>) -> IResult<Input<'a>, &'a Token<'a>> {
    // Implementation
}

fn match_token<'a>(kind: TokenKind) -> impl FnMut(Input<'a>) -> IResult<Input<'a>, &'a Token<'a>> {
    // Implementation
}

fn ident<'a>(input: Input<'a>) -> IResult<Input<'a>, &str> {
    // Implementation
}

fn main() {
    // Use the `rule!` macro
    let mut parser = rule!(
        CREATE ~ TABLE ~ #ident ~ ^"(" ~ (#ident ~ #ident ~ ","?)* ~ ")" ~ ";"
        : "CREATE TABLE statement"
    );
}

Syntax

The rule! macro follows these rules:

Syntax	Description	Expanded to	Operator Precedence
`TOKEN`	Matches a token by kind.	`match_token(TOKEN)`	-
`"("`	Matches a token by its text.	`match_text("(")`	-
`#fn_name`	Calls an external nom parser function `fn_name`.	`fn_name`	-
`#fn_name(a, b, c)`	Calls an external nom parser function `fn_name` with arguments.	`fn_name(a, b, c)`	-
`a ~ b ~ c`	Sequences parsers `a`, `b`, and `c`.	`nom::sequence::tuple((a, b, c))`	3 (Left Associative)
`a+`	One or more repetitions.	`nom::multi::many1(a)`	4 (Postfix)
`a*`	Zero or more repetitions.	`nom::multi::many0(a)`	4 (Postfix)
`a?`	Optional parser.	`nom::combinator::opt(a)`	4 (Postfix)
`a \| b \| c`	Choice between parsers `a`, `b`, and `c`.	`nom::branch::alt((a, b, c))`	1 (Left Associative)
`&a`	Peeks at parser `a` without consuming input.	`nom::combinator::peek(a)`	5 (Prefix)
`!a`	Negative lookahead for parser `a`.	`nom::combinator::not(a)`	5 (Prefix)
`^a`	Cuts the parser `a`.	`nom::combinator::cut(a)`	5 (Prefix)
`... : "description"`	Adds a context description for error reporting.	`nom::error::context("description", a)`	2 (Postfix)

Example

See the sqlparser.rs file for a complete example parsing a simplified SQL CREATE TABLE statement.

Dependencies

~1–1.6MB
~33K SLoC