ihateintegrals 0.1.2

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

use crate::{
    argument::Argument,
    derivation_rules::helpers::is_constant,
    expressions::{sum::sum_of, Exponent, Expression, Fraction, Integer},
};

use super::DerivationRule;

/**
* Reverse of the power rule.
*/
pub struct IntegralPowerRule {}

impl DerivationRule for IntegralPowerRule {
    fn apply(&self, input: Expression) -> Vec<(Expression, Rc<Argument>)> {
        let integral = match input {
            Expression::Integral(ref i) => i,
            _ => return vec![],
        };

        // This works only if the integrand is the change variable to some
        // constant power.
        let (base, power) = match integral.integrand() {
            Expression::Exponent(e) => {
                if e.base() == integral.variable() && is_constant(&e.power(), &integral.variable())
                {
                    (e.base(), e.power())
                } else {
                    return vec![];
                }
            }
            exp => {
                if exp == integral.variable() {
                    (exp, Integer::of(1))
                } else {
                    return vec![];
                }
            }
        };

        if let Expression::Negation(ref n) = power {
            if let Expression::Integer(i) = n.exp() {
                if i.value() == 1 {
                    return vec![];
                }
            }
        }

        vec![(
            Fraction::of(
                Exponent::of(base, sum_of(&[power.clone(), Integer::of(1)])),
                sum_of(&[power, Integer::of(1)]),
            ),
            Argument::new(String::from("Reverse power rule"), vec![input], self.name()),
        )]
    }

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

#[cfg(test)]
mod tests {
    use crate::{
        convenience_expressions::{i, power, v},
        derivation_rules::DerivationRule,
        expressions::{sum::sum_of, Fraction, Integral},
    };

    use super::IntegralPowerRule;

    #[test]
    fn test_1() {
        let start = Integral::of(v("x"), v("x"));
        let rule = IntegralPowerRule {};
        let result = rule.apply(start).first().unwrap().0.clone();

        assert_eq!(
            result,
            Fraction::of(power(v("x"), sum_of(&[i(1), i(1)])), sum_of(&[i(1), i(1)]))
        );

        let start2 = Integral::of(power(v("x"), i(3)), v("x"));
        let result2 = rule.apply(start2).first().unwrap().0.clone();

        assert_eq!(
            result2,
            Fraction::of(power(v("x"), sum_of(&[i(3), i(1)])), sum_of(&[i(3), i(1)]))
        );
    }
}