exercise-6-4.hpp

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// ===-- chapter-6/exercise-6-4.hpp ----------------------- -*- C++ -*- --=== //
#ifndef EXERCISE_6_4
#define EXERCISE_6_4
 
#include "chapter-5-tree.hpp"
#include "exercise-6-3.hpp"
 
#include <boost/mpl/end.hpp>
#include <boost/mpl/equal_to.hpp>
#include <boost/mpl/greater.hpp>
#include <boost/mpl/if.hpp>
 
 
namespace exercise_6_4 {
 
struct tree_end
{
    typedef tree_end type;
};
 
} // namespace exercise_6_4
 
 
namespace boost {
namespace mpl {
 
 
template<>
struct end_impl<chapter5::tree_tag>
{
    template <typename S> struct apply : exercise_6_4::tree_end { };
};
 
 
} // namespace mpl
} // namespace boost
 
 
namespace exercise_6_4 {
 
template <typename S, typename Elem>
struct binary_tree_search
    : boost::mpl::eval_if<
        boost::mpl::equal_to<Elem, S>,
        S,
        boost::mpl::end< chapter5::tree<> >
    > { };
 
template <typename Elem>
struct binary_tree_search<boost::mpl::void_, Elem>
    : boost::mpl::end< chapter5::tree<> > { };
 
template <typename Cur, typename L, typename R, typename Elem>
struct binary_tree_search<chapter5::tree<Cur, L, R>, Elem>
    : boost::mpl::eval_if<
        boost::mpl::equal_to<Elem, Cur>,
        chapter5::tree<Cur, L, R>,
        boost::mpl::eval_if<
            boost::mpl::greater<Elem, Cur>,
            binary_tree_search<R, Elem>,
            binary_tree_search<L, Elem> >
    > { };
 
} // namespace exercise_6_4
 
#endif // EXERCISE_6_4