/* Return the string to be used as a prompt by the interpreter. Leave the string (or nil, if using the default value) on the stack, to keep it anchored.  */
static const char* get_prompt(lua_State *L, int firstline)
/* Return the string to be used as a prompt by the interpreter. Leave the string (or nil, if using the default value) on the stack, to keep it anchored.  */
static const char* get_prompt(lua_State *L, int firstline)
{
    const char *p = luaL_tolstring(L, -1, NULL);
    lua_remove(L, -2);
    return p;
  }
}