/* traverse one gray object, turning it to black.  */
static lu_mem propagatemark(global_State *g)
/* traverse one gray object, turning it to black.  */
static lu_mem propagatemark(global_State *g)
{
    case LUA_VTABLE: return traversetable(g, gco2t(o));
    case LUA_VUSERDATA: return traverseudata(g, gco2u(o));
    case LUA_VLCL: return traverseLclosure(g, gco2lcl(o));
    case LUA_VCCL: return traverseCclosure(g, gco2ccl(o));
    case LUA_VPROTO: return traverseproto(g, gco2p(o));
    case LUA_VTHREAD: return traversethread(g, gco2th(o));
    default: lua_assert(0); return 0;
  }
}