tree.hpp

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#include <functional>
#include <iostream>
#include <string>

#ifndef DBG_TREE_HPP
#define DBG_TREE_HPP

const char vert_branch = '-';

template <typename T>
struct PrettyTree final
{
    PrettyTree (std::function<std::vector<T>(T&)> traverser,
        std::function<void(std::ostream&,T&)> to_stream) :
        traverser_(traverser), to_stream_(to_stream) {}

    void print (std::ostream& out, T root)
    {
        print_helper(out, root, "");
    }

    size_t branch_length_ = 2;

    std::function<std::vector<T>(T&)> traverser_;

    std::function<void(std::ostream&,T&)> to_stream_;

private:
    void print_helper (std::ostream& out, T root, std::string prefix)
    {
        out << "(";
        to_stream_(out, root);
        out << ")\n";
        std::vector<T> children = traverser_(root);
        size_t nchildren = children.size();
        if (nchildren > 0)
        {
            std::string branch = prefix + " `" +
                std::string(branch_length_, vert_branch);
            for (size_t i = 0; i < nchildren - 1; ++i)
            {
                out << branch;
                this->print_helper(out, children[i],
                    prefix + " |" + std::string(branch_length_, ' '));
            }
            out << branch;
            this->print_helper(out, children[nchildren - 1],
                prefix + std::string(2 + branch_length_, ' '));
        }
    }
};

#endif // DBG_TREE_HPP