#include "combine.hpp"

double combine(std::vector<double> const & xs, double (*mult)(double, double), double (*plus)(double, double)) {
    double sum = 0;

    size_t i = 1;
    while (i < xs.size()) {
        sum = plus(sum, mult (xs[i - 1], xs[i]));

        i += 2;
    }

    if (i - 1 < xs.size()) {
        sum = plus(sum, xs[i - 1]);
    }

    return sum;
}