semiring/src/counting.rs


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//! This module implements the "counting semiring", which counts the
//! number of ways a sentence can be derived by a grammar.

use super::*;

/// The counting semiring is a thin wrapper around the natural numbers
/// with the usual addition and multiplication.
#[derive(Copy, Clone, Debug, Ord, PartialOrd, Hash, Eq, PartialEq)]
pub struct Count(usize);

impl Count {
    /// Wrap the count in the wrapper.
    pub fn new(count: usize) -> Self {
        Self(count)
    }

    /// Extract the count out.
    pub fn value(&self) -> usize {
        self.0
    }
}

impl Semiring for Count {
    fn zero() -> Self {
        Self::new(0)
    }

    fn one() -> Self {
        Self::new(1)
    }

    fn add(&mut self, other: &Self) {
        self.0 = self.value() + other.value();
    }

    fn mul(&mut self, other: &Self) {
        self.0 = self.value() * other.value();
    }

    fn valuation(_pos: usize, _grammar: &Grammar) -> Self {
        Self::new(1)
    }
}