scala> val l = List()
l: List[Nothing] = List()
scala> l.forall(x=>false)
res0: Boolean = true
scala> l.forall(x=>true)
res1: Boolean = true
scala> l.exists(x=>false)
res2: Boolean = false
scala> l.exists(x=>true)
res3: Boolean = false
对于以上2个谓词,既然列表中不存在任何元素,那么forall怎么会返回true?我很困惑。你能帮忙解释一下吗?