C++ implementation of accumulator described in http://www.paulgraham.com/icad.html

01 accumulator generator.cpp

template<typename T>
struct Accumulator {
    Accumulator(T n) : n_{n} {}
    template <typename U>
    const T& operator()(const U& i) { return n_ += i; }
private:
    T n_;
};

template <typename T>
Accumulator<T> accumulator(const T& n) {
    return Accumulator<T>(n);
}

02 usage example.cpp

#include <iostream>

int main(int argc, char* argv[]) {
    auto acc = Accumulator<int>(10);
    std::cout << acc(2) << ", ";
    std::cout << acc(3.6) << std::endl;

    std::cout << accumulator(10.2)(1) << std::endl;

    std::cout << accumulator(std::string{"hello"})(std::string{", world"}) << std::endl;

    return 0;
}