compose3.h

// see http://earl.strain.at/space/2009-07-06

#include <functional>

template <typename F, typename G, typename H>
struct compose3_t : public std::binary_function<typename G::argument_type,
                                                typename H::argument_type,
                                                typename F::result_type> {
  F f;
  G g;
  H h;

  compose3_t(const F &f, const G &g, const H &h): f(f), g(g), h(h) {}

  typename F::result_type operator()(const typename G::argument_type &x,
                                     const typename H::argument_type &y) const {
    return f(g(x), h(y));
  }
};

template <typename F, typename G, typename H>
compose3_t<F, G, H> compose3(const F &f, const G &g, const H &h) {
  return compose3_t<F, G, H>(f, g, h);
}