README.md

Binomial Probability

Exercise to learn more about rust's type system. If you know a way to implement a trait on all itertors please tell me.

binomial_probability.rs

use std::ops::Range;
enum ConditionType {
    Number,
    Closure,
    Range,
}

trait Condition {
    fn r#type(&self) -> ConditionType;

    fn as_num(&self) -> i32 {
        unreachable!();
    }

    fn as_closure(&self) -> &dyn Fn(i32) -> bool {
        unreachable!();
    }

    fn as_range(&self) -> Range<i32> {
        unreachable!();
    }
}

impl Condition for i32 {
    fn r#type(&self) -> ConditionType {
        ConditionType::Number
    }

    fn as_num(&self) -> i32 {
        *self
    }
}

impl<F> Condition for F where F: Fn(i32) -> bool {
    fn r#type(&self) -> ConditionType {
        ConditionType::Closure
    }

    fn as_closure(&self) -> &dyn Fn(i32) -> bool {
        self
    }
}

impl Condition for Range<i32> {
    fn r#type(&self) -> ConditionType {
        ConditionType::Range
    }

    fn as_range(&self) -> Range<i32> {
        self.clone()
    }
}

fn factorial(n: i32) -> i32 {
    match n {
        0 => 1,
        _ => factorial(n - 1) * n,
    }
}

fn choose(n: i32, r: i32) -> i32 {
    factorial(n) / (factorial(r) * factorial(n - r))
}

fn binomial_probability(condition: impl Condition, total: i32, prob: f64) -> f64 {
    match condition.r#type() {
        ConditionType::Number => choose(total, condition.as_num()) as f64 * prob.powi(condition.as_num()) * (1. - prob).powi(total - condition.as_num()),
        ConditionType::Closure => {
                let mut res: f64 = 0.0;
                for i in 0..=total {
                    if condition.as_closure()(i) {
                            res += binomial_probability(i, total, prob);
                    }
                }
                res
        },
        ConditionType::Range => {
            let mut res: f64 = 0.0;
            for i in condition.as_range() {
                if(i <= total) { res += binomial_probability(i, total, prob); }
            }
            res
        }
    }
}