use num_traits::Zero;
use std::ops::{Add, Mul};

fn horner<Arr, Arg, Out>(v: &[Arr], x: Arg) -> Out
where
    Arr: Clone + Mul<Arr, Output = Arr> + Mul<Arg, Output = Arr> + Zero,
    Arg: Clone,
    Out: From<Arr>,
{
    v.iter()
        .rev()
        .fold(Arr::zero(), |acc, coeff| acc * x.clone() + coeff.clone())
        .into()
}

fn main() {
    let v = [-19., 7., -4., 6.];
    println!("result: {}", horner::<f32, f32, f64>(&v, 3.0));
}