Enum logos::FilterResult

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pub enum FilterResult<T, E> {
    Emit(T),
    Skip,
    Error(E),
}
Expand description

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

§Example

use logos::{Logos, FilterResult};

#[derive(Debug, PartialEq, Clone, Default)]
enum LexingError {
    NumberParseError,
    NumberIsTen,
    #[default]
    Other,
}

impl From<std::num::ParseIntError> for LexingError {
    fn from(_: std::num::ParseIntError) -> Self {
        LexingError::NumberParseError
    }
}

#[derive(Logos, Debug, PartialEq)]
#[logos(error = LexingError)]
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.
        if n % 2 == 0 {
            // Emit an error if `n` is 10.
            if n == 10 {
                FilterResult::Error(LexingError::NumberIsTen)
            } else {
                FilterResult::Emit(n)
            }
        } else {
            FilterResult::Skip
        }
    })]
    NiceEvenNumber(u64)
}

let tokens: Vec<_> = Token::lexer("20 11 42 23 100 10").collect();

assert_eq!(
    tokens,
    &[
        Ok(Token::NiceEvenNumber(20)),
        // skipping 11
        Ok(Token::NiceEvenNumber(42)),
        // skipping 23
        Ok(Token::NiceEvenNumber(100)),
        // error at 10
        Err(LexingError::NumberIsTen),
    ]
);

Variants§

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Emit(T)

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

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Skip

Skip current match, analog to Skip.

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Error(E)

Emit a <Token as Logos>::ERROR token.

Auto Trait Implementations§

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impl<T, E> Freeze for FilterResult<T, E>
where E: Freeze, T: Freeze,

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impl<T, E> RefUnwindSafe for FilterResult<T, E>

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impl<T, E> Send for FilterResult<T, E>
where E: Send, T: Send,

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impl<T, E> Sync for FilterResult<T, E>
where E: Sync, T: Sync,

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impl<T, E> Unpin for FilterResult<T, E>
where E: Unpin, T: Unpin,

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impl<T, E> UnwindSafe for FilterResult<T, E>
where E: UnwindSafe, T: UnwindSafe,

Blanket Implementations§

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impl<T> Any for T
where T: 'static + ?Sized,

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fn type_id(&self) -> TypeId

Gets the TypeId of self. Read more
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impl<T> Borrow<T> for T
where T: ?Sized,

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fn borrow(&self) -> &T

Immutably borrows from an owned value. Read more
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impl<T> BorrowMut<T> for T
where T: ?Sized,

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fn borrow_mut(&mut self) -> &mut T

Mutably borrows from an owned value. Read more
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impl<T> From<T> for T

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fn from(t: T) -> T

Returns the argument unchanged.

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impl<T, U> Into<U> for T
where U: From<T>,

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fn into(self) -> U

Calls U::from(self).

That is, this conversion is whatever the implementation of From<T> for U chooses to do.

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impl<T, U> TryFrom<U> for T
where U: Into<T>,

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type Error = Infallible

The type returned in the event of a conversion error.
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fn try_from(value: U) -> Result<T, <T as TryFrom<U>>::Error>

Performs the conversion.
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impl<T, U> TryInto<U> for T
where U: TryFrom<T>,

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type Error = <U as TryFrom<T>>::Error

The type returned in the event of a conversion error.
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fn try_into(self) -> Result<U, <U as TryFrom<T>>::Error>

Performs the conversion.