Simple example of using nom, Rust parser combinator

README.md

An example of how to use nom to create parsers in Rust

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Cargo.toml

[package]
name = "learning-nom"
version = "0.1.0"
edition = "2021"

# See more keys and their definitions at https://doc.rust-lang.org/cargo/reference/manifest.html

[dependencies]
nom = "7.1.2"

main.rs

// src/main.rs

use nom::{
    branch::permutation,
    bytes::complete::tag_no_case,
    character::complete::{alpha1, digit1, space0},
    combinator::{map_res, opt},
    sequence::tuple,
    IResult,
};

#[derive(Debug)]
struct Person {
    name: String,
    age: u8,
    language: String,
}

fn and_parser(input: &str) -> IResult<&str, ()> {
    let (input, _) = opt(tag_no_case(" and "))(input)?;
    Ok((input, ()))
}

fn age_parser(input: &str) -> IResult<&str, u8> {
    let (input, _) = and_parser(input)?;
    let (input, _) = tuple((space0, tag_no_case("i am ")))(input)?;
    let (input, age) = map_res(digit1, |x: &str| x.parse::<u8>())(input)?;
    let (input, _) = tag_no_case(" years old")(input)?;

    Ok((input, age))
}

fn language_parse(input: &str) -> IResult<&str, String> {
    let (input, _) = and_parser(input)?;
    let (input, _) = tuple((space0, tag_no_case("i like ")))(input)?;
    let (input, language) = alpha1(input)?;

    Ok((input, language.to_string()))
}

fn name_parser(input: &str) -> IResult<&str, String> {
    let (input, _) = and_parser(input)?;
    let (input, _) = tuple((space0, tag_no_case("my name is ")))(input)?;
    let (input, name) = alpha1(input)?;
    Ok((input, name.to_string()))
}

fn parse_person(input: &str) -> IResult<&str, Person> {
    let (input, _) = tag_no_case("Hello, ")(input)?;
    let (input, (name, age, language)) =
        permutation((name_parser, age_parser, language_parse))(input)?;

    Ok((
        input,
        Person {
            name,
            age,
            language,
        },
    ))
}

fn main() {
    let testdata = [
        "Hello, my name is Tommaso and i am 32 years old and I like Rust",
        "Hello, my name is Roberto and i like Python and I am 44 years old",
        "Hello, I like JavaScript my name is Luciano I am 35 years old",
    ];

    for input in testdata.iter() {
        let (_, person) = parse_person(input).unwrap();
        println!("{:?}", person);
    }
    
    // Outputs:
    // Person { name: "Tommaso", age: 32, language: "Rust" }
    // Person { name: "Roberto", age: 44, language: "Python" }
    // Person { name: "Luciano", age: 35, language: "JavaScript" }
}