void instr()
{
    MIN_ARGUMENTS(1);

    // stringify only if not already a string
    if (_stack->get_type(0) != cmd_string)
    {
        // write the object in stack(0) in a string and remove this obj
        FILE* tmp = tmpfile();
        if (tmp != NULL)
        {
            ((object*)_stack->pop_back())->show(tmp);

            // reserve the correct size in stack
            unsigned int str_size = (unsigned int)ftell(tmp);
            ostring* str = (ostring*)_stack->allocate_back(str_size+1+sizeof(ostring), cmd_string);
            str->_size = str_size;

            // fill the obj
            if (fread(str->_value, str_size, 1, tmp) != str_size)
                ERR_CONTEXT(ret_runtime_error);
            fclose(tmp);
        }
        else
            ERR_CONTEXT(ret_runtime_error);
    }
}

void strout()
{
    MIN_ARGUMENTS(1);
    ARG_MUST_BE_OF_TYPE(0, cmd_string);

    string entry(((ostring*)_stack->pop_back())->_value);

    program prog;

    // make program from string in stack level 1
    if (program::parse(entry.c_str(), prog) == ret_ok)
        // run it
        prog.run(*_stack, *_global_heap, &_local_heap);
}