ihateintegrals 0.1.2

A computer algebra library for solving integrals.
Documentation 
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use std::rc::Rc;

use crate::{
    argument::Argument,
    expressions::{
        product::{product_of, product_of_iter},
        sum::sum_of,
        Expression,
    },
};

use super::DerivationRule;

pub struct Foil {}

/**
* (a+b)(c+d) = ac + ad + bc + bd
*/
impl DerivationRule for Foil {
    fn apply(&self, input: Expression) -> Vec<(Expression, Rc<Argument>)> {
        let product = match input {
            Expression::Product(ref p) => p,
            _ => return vec![],
        };

        let (sums, non_sums) = {
            let mut sums = Vec::new();
            let mut non_sums = Vec::new();
            for factor in product.factors() {
                match factor {
                    Expression::Sum(_) => sums.push(factor.clone()),
                    _ => non_sums.push(factor.clone()),
                }
            }
            (sums, non_sums)
        };

        // Foil every pair of sums
        let mut equivalents = Vec::<Expression>::new();

        for first in &sums {
            for second in &sums {
                if first == second {
                    continue;
                }
                let first_sum = match first {
                    Expression::Sum(ref s) => s,
                    _ => panic!(),
                };
                let second_sum = match second {
                    Expression::Sum(ref s) => s,
                    _ => panic!(),
                };
                let excluded_sums = sums
                    .iter()
                    .filter(|s| *s != first && *s != second)
                    .map(|s| (*s).clone())
                    .collect::<Vec<Expression>>();
                // FOIL
                let mut new_terms = Vec::<Expression>::new();

                for term in first_sum.terms() {
                    for other in second_sum.terms() {
                        new_terms.push(product_of(&[term.clone(), other.clone()]));
                    }
                }

                equivalents.push(product_of_iter(
                    &mut [sum_of(&new_terms)]
                        .into_iter()
                        .chain(non_sums.to_vec())
                        .chain(excluded_sums),
                ))
            }
        }

        equivalents
            .iter()
            .map(|expression| {
                (
                    expression.clone(),
                    Argument::new(String::from("FOIL"), vec![input.clone()], self.name()),
                )
            })
            .collect::<Vec<(Expression, Rc<Argument>)>>()
    }

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

#[cfg(test)]
mod tests {
    use super::*;
    use crate::{convenience_expressions::v, derivation_rules::DerivationRule};

    #[test]
    fn test_1() {
        let rule = Foil {};
        let start = product_of(&[sum_of(&[v("a"), v("b")]), sum_of(&[v("c"), v("d")])]);
        let result = rule.apply(start);
        assert_eq!(
            result.first().unwrap().0,
            sum_of(&[
                product_of(&[v("a"), v("c")]),
                product_of(&[v("a"), v("d")]),
                product_of(&[v("b"), v("c")]),
                product_of(&[v("b"), v("d")]),
            ])
        );
    }
}