third_party/rust_crates/tiny_mirrors/nom_locate/README.md

# nom_locate

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A special input type for [nom](https://github.com/geal/nom) to locate tokens

## Documentation

The documentation of the crate is available [here](https://docs.rs/nom_locate/).

## How to use it
The crate provide the [`LocatedSpan` struct](https://docs.rs/nom_locate/struct.LocatedSpan.html) that encapsulates the data. Look at the below example and the explanations:

````rust
extern crate nom;
extern crate nom_locate;

use nom::bytes::complete::{tag, take_until};
use nom::IResult;
use nom_locate::{position, LocatedSpan};

type Span<'a> = LocatedSpan<&'a str>;

struct Token<'a> {
    pub position: Span<'a>,
    pub foo: &'a str,
    pub bar: &'a str,
}

fn parse_foobar(s: Span) -> IResult<Span, Token> {
    let (s, _) = take_until("foo")(s)?;
    let (s, pos) = position(s)?;
    let (s, foo) = tag("foo")(s)?;
    let (s, bar) = tag("bar")(s)?;

    Ok((
        s,
        Token {
            position: pos,
            foo: foo.fragment,
            bar: bar.fragment,
        },
    ))
}

fn main() {
    let input = Span::new("Lorem ipsum \n foobar");
    let output = parse_foobar(input);
    let position = output.unwrap().1.position;
    assert_eq!(
        position,
        Span {
            offset: 14,
            line: 2,
            fragment: "",
            extra: (),
        }
    );
    assert_eq!(position.get_column(), 2);
}
````

### Import

Import [nom](https://github.com/geal/nom) and nom_locate.

````rust
extern crate nom;
extern crate nom_locate;

use nom::bytes::complete::{tag, take_until};
use nom::IResult;
use nom_locate::{position, LocatedSpan};
````

Also you'd probably create [type alias](https://doc.rust-lang.org/book/type-aliases.html) for convenience so you don't have to specify the `fragment` type every time:

````rust
type Span<'a> = LocatedSpan<&'a str>;
````

### Define the output structure

The output structure of your parser may contain the position as a `Span` (which provides the `index`, `line` and `column` information to locate your token).

````rust
struct Token<'a> {
    pub position: Span<'a>,
    pub foo: &'a str,
    pub bar: &'a str,
}
````

### Create the parser

The parser has to accept a `Span` as an input. You may use `position()` in your nom parser, in order to capture the location of your token:

````rust
fn parse_foobar(s: Span) -> IResult<Span, Token> {
    let (s, _) = take_until("foo")(s)?;
    let (s, pos) = position(s)?;
    let (s, foo) = tag("foo")(s)?;
    let (s, bar) = tag("bar")(s)?;

    Ok((
        s,
        Token {
            position: pos,
            foo: foo.fragment,
            bar: bar.fragment,
        },
    ))
}
````

### Call the parser

The parser returns a `nom::IResult<Token, _>` (hence the `unwrap().1`). The `position` property contains the `offset`, `line` and `column`.

````rust
fn main () {
    let input = Span::new("Lorem ipsum \n foobar");
    let output = parse_foobar(input);
    let position = output.unwrap().1.position;
    assert_eq!(position, Span {
        offset: 14,
        line: 2,
        fragment: ""
    });
    assert_eq!(position.get_column(), 2);
}
````