ihateintegrals 0.1.2

A computer algebra library for solving integrals.
Documentation 
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use crate::{
    argument::Argument,
    expressions::{Expression, Integer},
};

use super::DerivationRule;

/**
* x * 0 = 0
*/
pub struct AnythingTimesZero {}

impl DerivationRule for AnythingTimesZero {
    fn apply(
        &self,
        input: crate::expressions::Expression,
    ) -> Vec<(
        crate::expressions::Expression,
        std::rc::Rc<crate::argument::Argument>,
    )> {
        let product = match input {
            Expression::Product(ref p) => p,
            _ => return vec![],
        };

        let is_zero = product.factors().contains(&Integer::of(0));

        if !is_zero {
            return vec![];
        }

        vec![(
            Integer::of(0),
            Argument::new(
                String::from("anything times zero is zero"),
                vec![input],
                self.name(),
            ),
        )]
    }

    fn name(&self) -> String {
        String::from("AnythingTimesZero")
    }
}

#[cfg(test)]
mod tests {
    use crate::{
        derivation_rules::DerivationRule,
        expressions::{Expression, Integer, Product},
    };

    use super::AnythingTimesZero;

    #[test]
    fn test_1() {
        let rule = AnythingTimesZero {};

        let to_zero = Product::of(&[Integer::of(1), Integer::of(0)]).unwrap();
        let not_zero = Product::of(&[Integer::of(1), Integer::of(1)]).unwrap();

        let result1: Vec<Expression> = rule.apply(to_zero).iter().map(|x| x.0.clone()).collect();
        let result2: Vec<Expression> = rule.apply(not_zero).iter().map(|x| x.0.clone()).collect();

        assert_eq!(result1[0], Integer::of(0));
        assert_eq!(result1.len(), 1);
        assert_eq!(result2.len(), 0);
    }
}