Enum logos::Filter

pub enum Filter<T> {
    Emit(T),
    Skip,
}

Type that can be returned from a callback, either producing a field for a token, or skipping it.

Example

use logos::{Logos, Filter};

#[derive(Logos, Debug, PartialEq)]
enum Token {
    #[regex(r"[ \n\f\t]+", logos::skip)]
    Ignored,

    #[regex("[0-9]+", |lex| {
        let n: u64 = lex.slice().parse().unwrap();

        // Only emit a token if `n` is an even number
        match n % 2 {
            0 => Filter::Emit(n),
            _ => Filter::Skip,
        }
    })]
    EvenNumber(u64)
}

let tokens: Vec<_> = Token::lexer("20 11 42 23 100 8002").collect();

assert_eq!(
    tokens,
    &[
        Ok(Token::EvenNumber(20)),
        // skipping 11
        Ok(Token::EvenNumber(42)),
        // skipping 23
        Ok(Token::EvenNumber(100)),
        Ok(Token::EvenNumber(8002))
    ]
);

Variants

Emit(T)

Emit a token with a given value T. Use () for unit variants without fields.

Skip

Skip current match, analog to Skip.