proc visualize_lisp_machine() -> void {
    struct Drawn_Area {
        int x;
        int y;
        int width;
        int height;
    };

    fprintf(stderr, "Drawing visualization...");
    defer {
        fprintf(stderr, "Done!\n");
    };

    const int padding = 40;
    const int margin  = 20;

    const char* draw_text_template    = "  <text x='%d' y='%d' font-size='20' font-family='monospace' style='fill: %s'>\n   %s%s%s\n  </text>\n";
    const char* draw_integer_template = "  <text x='%d' y='%d' font-size='20' font-family='monospace'>\n    %d\n  </text>\n";
    const char* draw_float_template   = "  <text x='%d' y='%d' font-size='20' font-family='monospace'>\n    %012.6f\n  </text>\n";


    FILE *f = fopen("visualization.svg", "w");
    defer {
        fclose(f);
    };

    if (f == NULL) {
        create_generic_error("The file for writing the visualization"
                             "could not be opened for writing");
        return;
    }

    int max_x   = 0,
        max_y   = 0,
        write_x = 0,
        write_y = 0;


    proc draw_margin = [&](int count = 1) -> Drawn_Area {
        write_x += margin * count;
        return {
            write_x - margin * count,
            write_y,
            margin * count,
            write_y
        };
    };
    proc draw_new_line = [&](int count = 1) {
        write_x = 0;
        write_y += 25 * count;
    };
    proc draw_text = [&](const char* text, const char* color = "#000000", bool draw_quotes = false, int max_length = 200) -> Drawn_Area {
        // take care of escaping sensitive chars
        int text_length = 0;
        int extra_needed_chars = draw_quotes ? 10 : 0;
        char* new_text = nullptr;
        char char_at_max_length = 0;

        char source;
        while ((source = text[text_length++]) != '\0') {
            switch (source) {
            case '\n':
                extra_needed_chars += 1;
            case '<':
            case '>':
                extra_needed_chars += 3;
                break;
            case '&':
                extra_needed_chars += 4;
                break;
            case '\'':
            case '"':
                extra_needed_chars += 5;
            }
        }
        // last char was \0 but we don't count it
        --text_length;

        if (text_length > max_length) {
            char_at_max_length = ((char*)text)[max_length];
            ((char*)text)[max_length] = '\0';
            text_length = max_length;
        }
        defer {
            if (char_at_max_length)
                ((char*)text)[max_length] = char_at_max_length;
        };

        // if we need to replace some chars
        if (extra_needed_chars > 0) {
            new_text = (char*)malloc((text_length + extra_needed_chars) * sizeof(char));

            int index_in_text     = 0,
                index_in_new_text = 0;

            char source;
            while ((source = text[index_in_text++]) != '\0') {
                switch (source) {
                case '\n': new_text[index_in_new_text++] = '\\'; new_text[index_in_new_text++] = 'n'; break;
                case '<':  new_text[index_in_new_text++] = '&';  new_text[index_in_new_text++] = 'l'; new_text[index_in_new_text++] = 't'; new_text[index_in_new_text++] = ';'; break;
                case '>':  new_text[index_in_new_text++] = '&';  new_text[index_in_new_text++] = 'g'; new_text[index_in_new_text++] = 't'; new_text[index_in_new_text++] = ';'; break;
                case '&':  new_text[index_in_new_text++] = '&';  new_text[index_in_new_text++] = 'a'; new_text[index_in_new_text++] = 'm'; new_text[index_in_new_text++] = 'p'; new_text[index_in_new_text++] = ';'; break;
                case '"':  new_text[index_in_new_text++] = '&';  new_text[index_in_new_text++] = 'q'; new_text[index_in_new_text++] = 'u'; new_text[index_in_new_text++] = 'o'; new_text[index_in_new_text++] = 't'; new_text[index_in_new_text++] = ';'; break;
                case '\'': new_text[index_in_new_text++] = '&';  new_text[index_in_new_text++] = 'a'; new_text[index_in_new_text++] = 'p'; new_text[index_in_new_text++] = 'o'; new_text[index_in_new_text++] = 's'; new_text[index_in_new_text++] = ';'; break;
                default:   new_text[index_in_new_text++] = source;
                }
            }
            new_text[index_in_new_text] = '\0';
        }

        int text_width  = 12 * (text_length + (draw_quotes ? 2 : 0));
        if (write_x + text_width > max_x) max_x = write_x + text_width;
        if (write_y + 12 > max_y) max_y = write_y + 12;

        const char* quote = draw_quotes ? "&quot;" : "";
        if (extra_needed_chars) {
            fprintf(f, draw_text_template, write_x, write_y+12, color, quote, new_text, quote);
            free(new_text);
        } else {
            fprintf(f, draw_text_template, write_x, write_y+12, color, quote, text, quote, color);
        }

        // write_x += text_width;

        return {
            write_x - text_width,
            write_y,
            text_width,
            12
        };
    };
    proc draw_integer = [&](int number) -> Drawn_Area {
        int text_width  = 12 * ((int)log10(number)+1);

        if (write_x + text_width > max_x) max_x = write_x + text_width;
        if (write_y > max_y) max_y = write_y;

        fprintf(f, draw_integer_template, write_x, write_y+12, number);

        return {
            write_x,
            write_y,
            text_width,
            12
        };
    };
    proc draw_float = [&](float number) -> Drawn_Area {
        int text_width  = 12 * 12;

        if (write_x + text_width > max_x) max_x = write_x + text_width;
        if (write_y > max_y) max_y = write_y;

        fprintf(f, draw_float_template, write_x, write_y+12, number);

        return {
            write_x,
            write_y,
            text_width,
            12
        };
    };
    std::function<Drawn_Area(Lisp_Object*)> draw_pair;
    proc draw_lisp_object = [&](Lisp_Object* obj) -> Drawn_Area {
        switch (Memory::get_type(obj)) {
        case Lisp_Object_Type::T:       return draw_text("t");
        case Lisp_Object_Type::Nil:     return draw_text("()");
        case Lisp_Object_Type::Pair:    return draw_pair(obj);
        case Lisp_Object_Type::Number:  return draw_float(obj->value.number);
        case Lisp_Object_Type::Symbol:  return draw_text(&obj->value.string->data);
        case Lisp_Object_Type::Keyword: {
            Drawn_Area colon =  draw_text(":", "#c61b6e");
            write_x += colon.width;
            Drawn_Area text = draw_text(&obj->value.identifier->data, "#c61b6e");
            write_x -= colon.width;
            return {
                colon.x,
                colon.y,
                colon.width + text.width,
                colon.height
            };
        }
        case Lisp_Object_Type::String:  return draw_text(&obj->value.string->data, "#2aa198", true, 20);
        default: return {0};
        }
    };
    draw_pair = [&](Lisp_Object* pair) -> Drawn_Area {
        Drawn_Area ret;
        Drawn_Area child;

        ret.x = write_x;
        ret.y = write_y;
        ret.width = 100;
        ret.height = 100;

        fprintf(f,
                "  <rect x='%d' y='%d' width='100' height='50' stroke-width='3' stroke='black' fill='white'/>"
                "  <line x1='%d' y1='%d' x2='%d' y2='%d' stroke-width='3' stroke='black'/>",
                write_x, write_y, write_x+50, write_y, write_x+50, write_y+50);

        // arrow to first
        fprintf(f,
                "  <line x1='%d' y1='%d' x2='%d' y2='%d' stroke-width='3' stroke='black'/>",
                write_x+25, write_y+25, write_x+25, write_y+100);

        write_y += 110;
        child = draw_lisp_object(pair->value.pair.first);
        if (ret.width < child.width)
            ret.width = child.width;
        if (ret.height < child.height)
            ret.height = child.height;

        write_y -= 110;

        if (pair->value.pair.rest == Memory::nil) {
            fprintf(f,
                    "  <line x1='%d' y1='%d' x2='%d' y2='%d' stroke-width='3' stroke='black'/>",
                    write_x+50, write_y+50, write_x+100, write_y);
        } else {
            // arrow to rest
            int x_offset = 150;
            if (child.width+margin > x_offset)
                x_offset = child.width+margin;

            fprintf(f,
                    "  <line x1='%d' y1='%d' x2='%d' y2='%d' stroke-width='3' stroke='black'/>",
                    write_x+75, write_y+25, write_x+75+x_offset, write_y+25);

            write_x += x_offset;
            ret.width += 50;

            child = draw_lisp_object(pair->value.pair.rest);
            ret.width += child.width;
            if (ret.height < 70 + child.height)
                ret.height = 70 + child.height;

            write_x -= x_offset;
        }

        fprintf(f, "\n");

        if (max_x < ret.x + ret.width)
            max_x = ret.x + ret.width;
        if (max_y < ret.y + ret.height)
            max_y = ret.y + ret.height;

        return ret;
    };
    proc draw_header = [&]() {
        proc draw_separator = [&]() {
            draw_margin();
            draw_text("|");
            draw_margin();
        };

        time_t t = time(NULL);
        struct tm tm = *localtime(&t);

        write_y = 12;

        // -------------------
        //     Date
        // -------------------
        char date[12];
        snprintf(date, 12, "%02d.%02d.%d", tm.tm_mday, tm.tm_mon + 1, tm.tm_year + 1900);

        write_x += draw_text("Date: ").width;
        write_x += draw_text(date).width;

        draw_separator();

        // -------------------
        //     Time
        // -------------------
        char time[12];
        snprintf(time, 12, "%02d:%02d:%02d", tm.tm_hour, tm.tm_min, tm.tm_sec);

        write_x += draw_text("Time: ").width;
        write_x += draw_text(time).width;

        draw_separator();

        // -------------------
        //     String Memory
        // -------------------
        draw_new_line();

        int free_string_memory = Memory::next_free_spot_in_string_memory - Memory::string_memory;
        for (int i = 0; i < Memory::free_spots_in_string_memory->next_index; ++i) {
            free_string_memory += ((String*)(Memory::free_spots_in_string_memory->data[i]))->length;
        }
        int used_string_memory = Memory::string_memory_size - free_string_memory;

        write_x += draw_text("String Memory:").width;
        draw_margin();
        write_x += draw_text("[allocated chars] ").width;
        write_x += draw_integer(Memory::string_memory_size).width;
        draw_margin();
        write_x += draw_text("[free] ").width;
        write_x += draw_integer(free_string_memory).width;
        draw_margin();
        write_x += draw_text("[used] ").width;
        write_x += draw_integer(used_string_memory).width;
        draw_margin();
        write_x += draw_text("[%free] ").width;
        write_x += draw_float(100.0f * free_string_memory / Memory::string_memory_size).width;
        draw_margin();
        write_x += draw_text("[%used] ").width;
        write_x += draw_float(100.0f * used_string_memory / Memory::string_memory_size).width;

        draw_separator();
        draw_new_line();

        // -------------------
        //     Object Memory
        // -------------------

        int free_object_memory_cells = Memory::object_memory_size - (Memory::next_index_in_object_memory - Memory::free_spots_in_object_memory->next_index);
        int used_object_memory_cells = Memory::next_index_in_object_memory - Memory::free_spots_in_object_memory->next_index;

        write_x += draw_text("Object Memory:").width;
        draw_margin();
        write_x += draw_text("[#allocated] ").width;
        write_x += draw_integer(Memory::object_memory_size).width;
        draw_margin();
        write_x += draw_text("[#free] ").width;
        write_x += draw_integer(free_object_memory_cells).width;
        draw_margin();
        write_x += draw_text("[#used] ").width;
        write_x += draw_integer(used_object_memory_cells).width;
        draw_margin();
        write_x += draw_text("[%free] ").width;
        write_x += draw_float(100.0f * free_object_memory_cells / Memory::object_memory_size).width;
        draw_margin();
        write_x += draw_text("[%used] ").width;
        write_x += draw_float(100.0f * used_object_memory_cells / Memory::object_memory_size).width;

        draw_separator();

        draw_new_line(3);
    };
    proc draw_symbols_keywords_and_numbers = [&]() {
        Lisp_Object_Array_List* symbols  = create_Lisp_Object_array_list();
        Lisp_Object_Array_List* keywords = create_Lisp_Object_array_list();
        Lisp_Object_Array_List* numbers  = create_Lisp_Object_array_list();
        Lisp_Object_Array_List* strings  = create_Lisp_Object_array_list();
        Lisp_Object_Array_List* pairs    = create_Lisp_Object_array_list();
        Lisp_Object_Array_List* lists    = create_Lisp_Object_array_list();

        // loop over all used memory
        for (int i = 0; i < Memory::next_index_in_object_memory; ++i) {
            for (int j = 0; j < Memory::free_spots_in_object_memory->next_index; ++j) {
                if (i == Memory::free_spots_in_object_memory->data[j])
                    goto next;
            }

            switch (Memory::get_type(Memory::object_memory+i)) {
            case Lisp_Object_Type::Symbol:  append_to_array_list(symbols,  Memory::object_memory+i); break;
            case Lisp_Object_Type::String:  append_to_array_list(strings,  Memory::object_memory+i); break;
            case Lisp_Object_Type::Keyword: append_to_array_list(keywords, Memory::object_memory+i); break;
            case Lisp_Object_Type::Number : append_to_array_list(numbers,  Memory::object_memory+i); break;
            case Lisp_Object_Type::Pair :   append_to_array_list(pairs,    Memory::object_memory+i); break;
            default: break;
            }

          next: ;
        }

        // create the lists-list by filtering the pairs-list.
        Lisp_Object_Array_List* pairs_to_filter = create_Lisp_Object_array_list();
        Int_Array_List* indices_to_filter = create_Int_array_list();

        // helper lambda:
        proc remove_doubles_from_lisp_object_array_list = [&](Lisp_Object_Array_List* list) -> void {
            if (list->next_index == 0)
                return;

            sort_array_list(list);
            Int_Array_List* indices_to_filter = create_Int_array_list();

            size_t last = (size_t)list->data[0];
            for (int i = 1; i < list->next_index; ++i) {
                if ((size_t)list->data[i] == last)
                    append_to_array_list(indices_to_filter, i);
                else
                    last = (size_t)list->data[i];
            }

            for (int i = indices_to_filter->next_index; i >= 0; --i) {
                remove_index_from_array_list(list, indices_to_filter->data[i]);
            }

            // sort again as removing items destroys the order
            sort_array_list(list);
        };

        // recursive lambda
        std::function<void(Lisp_Object*)> filter_pair_and_children;
        filter_pair_and_children = [&](Lisp_Object* pair) {
            append_to_array_list(pairs_to_filter, pair);

            if (Memory::get_type(pair->value.pair.first) == Lisp_Object_Type::Pair)
                filter_pair_and_children(pair->value.pair.first);

            if (Memory::get_type(pair->value.pair.rest) == Lisp_Object_Type::Pair)
                filter_pair_and_children(pair->value.pair.rest);
        };
        for (int i = 0; i < pairs->next_index; ++i) {
            if (Memory::get_type(pairs->data[i]->value.pair.first) == Lisp_Object_Type::Pair)
                filter_pair_and_children(pairs->data[i]->value.pair.first);

            if (Memory::get_type(pairs->data[i]->value.pair.rest) == Lisp_Object_Type::Pair)
                filter_pair_and_children(pairs->data[i]->value.pair.rest);

        }

        remove_doubles_from_lisp_object_array_list(pairs_to_filter);
        // fprintf(stderr, "removing %d pairs\n", pairs_to_filter->next_index);
        // okay, so pairs_to_filter now only the pairs once each that
        // we want to filter from the pairs list
        for (int i = 0; i < pairs->next_index; ++i) {
            if (sorted_array_list_find(pairs_to_filter, pairs->data[i]) == -1) {
                append_to_array_list(lists, pairs->data[i]);
            }
        }

        draw_text("Memory Contents:");
        draw_new_line();
        draw_new_line();

        int start_x = write_x,
            start_y = write_y;

        write_x += draw_text("Symbols: ").width;
        draw_integer(symbols->next_index);
        draw_new_line();
        write_x = start_x;

        for (int i = 0; i < symbols->next_index; ++i) {
            draw_new_line();
            write_x = start_x;

            draw_text(&symbols->data[i]->value.identifier->data);
        }


        write_x = start_x + 300;
        write_y = start_y;

        write_x += draw_text("Keywords: ").width;
        draw_integer(keywords->next_index);
        draw_new_line();
        write_x = start_x + 300;

        for (int i = 0; i < keywords->next_index; ++i) {
            draw_new_line();
            write_x = start_x + 300;

            draw_lisp_object(keywords->data[i]);
        }



        write_x = start_x + 600;
        write_y = start_y;

        write_x += draw_text("Numbers: ").width;
        draw_integer(numbers->next_index);
        draw_new_line();
        write_x = start_x + 600;

        for (int i = 0; i < numbers->next_index; ++i) {
            draw_new_line();
            write_x = start_x + 600;

            draw_float(numbers->data[i]->value.number);
        }

        write_x = start_x + 900;
        write_y = start_y;

        write_x += draw_text("Strings: ").width;
        draw_integer(strings->next_index);
        draw_new_line();
        write_x = start_x + 900;

        for (int i = 0; i < strings->next_index; ++i) {
            draw_new_line();
            write_x = start_x + 900;

            draw_text(&strings->data[i]->value.string->data, "#2aa198", true, 75);
        }


        write_x = start_x + 2000;
        write_y = start_y;

        write_x += draw_text("Lists, Pairs: ").width;
        write_x += draw_integer(lists->next_index).width;
        draw_margin();
        draw_integer(pairs->next_index);
        draw_new_line();
        write_x = start_x + 2000;

        for (int i = 0; i < lists->next_index; ++i) {
            draw_new_line(3);
            write_x = start_x + 2000;

            write_y += draw_pair(lists->data[i]).height;
        }
    };

    fprintf(f,
            "<?xml version='1.0' encoding='UTF-8'?>\n"
            "<svg xmlns='http://www.w3.org/2000/svg'\n"
            "     version='1.1' baseProfile='full'\n"
            "     viewBox='%012d %012d %012d %012d'"
            ">\n\n", -padding, -padding, 0, 0);

    draw_header();
    draw_symbols_keywords_and_numbers();
    // draw_text("DoEun", "#00aaaa", true);

    fprintf(f, "\n\n</svg>");

    // fill in the correct viewBox
    rewind(f);

    fprintf(f,
            "<?xml version='1.0' encoding='UTF-8'?>\n"
            "<svg xmlns='http://www.w3.org/2000/svg'\n"
            "     version='1.1' baseProfile='full'\n"
            "     viewBox='%012d %012d %012d %012d'"
            ">", -padding, -padding, max_x + 2*padding, max_y + 2*padding);

}