doesn't have to和haven't to
因为在新概念65课中有一句‘so it was fortunate that we didn't have to carry him.’当然这句话的意思是,幸运的是我们不必抬起他.可是当我看到didn't have to这种说法时候觉得有点奇怪,但是这是书上写的形式,我想应该是正确的.所以我想知道haven't to是不是不正规的说法,或者说我认为haven't应该只有一个“没有”的意思,不存在haven't to是“不必”的意思.