nom-recursive

Extension of nom to handle left recursion.

Requirement

nom must be 5.0.0 or later. nom-recursive can be applied to function-style parser only.

The input type of nom parser must implement HasRecursiveInfo trait. Therefore &str and &[u8] can't be used. You can define a wrapper type of &str or &[u8] and implement HasRecursiveInfo.

Alternatively you can use nom_locate::LocatedSpan<T, RecursiveInfo>. This implements HasRecursiveInfo in this crate.

Usage

[dependencies]
nom-recursive = "0.5.1"

Example

use nom::branch::*;
use nom::character::complete::*;
use nom::IResult;
use nom_locate::LocatedSpan;
use nom_recursive::{recursive_parser, RecursiveInfo};

// Input type must implement trait HasRecursiveInfo
// nom_locate::LocatedSpan<T, RecursiveInfo> implements it.
type Span<'a> = LocatedSpan<&'a str, RecursiveInfo>;

pub fn expr(s: Span) -> IResult<Span, String> {
    alt((expr_binary, term))(s)
}

// Apply recursive_parser by custom attribute
#[recursive_parser]
pub fn expr_binary(s: Span) -> IResult<Span, String> {
    let (s, x) = expr(s)?;
    let (s, y) = char('+')(s)?;
    let (s, z) = expr(s)?;
    let ret = format!("{}{}{}", x, y, z);
    Ok((s, ret))
}

pub fn term(s: Span) -> IResult<Span, String> {
    let (s, x) = char('1')(s)?;
    Ok((s, x.to_string()))
}

fn main() {
    let ret = expr(LocatedSpan::new_extra("1+1", RecursiveInfo::new()));
    println!("{:?}", ret.unwrap().1);
}

License

Licensed under either of

Apache License, Version 2.0, (LICENSE-APACHE or http://www.apache.org/licenses/LICENSE-2.0)
MIT license (LICENSE-MIT or http://opensource.org/licenses/MIT)

at your option.

Contribution