Question

为了学习，我写了一个Scala代码

package pk

abstract class tree {
  def contains(x: Int): Boolean

  def incl(x: Int): tree

  def union(other: tree): tree
}

class empty extends tree {
  def contains(x: Int): Boolean = false

  def incl(x: Int): tree = new nonEmpty(x, new empty, new empty)

  override def toString = "."

  def union(other: tree): tree = {
    other
  }
}

class nonEmpty(elem: Int, left: tree, right: tree) extends tree {
  def contains(x: Int): Boolean = {
    if (x < elem) left contains x
    else if (x > elem) right contains x
    else true
  }

  def incl(x: Int): tree = {
    if (x < elem) new nonEmpty(elem, left incl x, right)
    else if (x > elem) new nonEmpty(elem, left, right incl x)
    else
      this
  }

  def union(other: tree): tree = {
    ((left union right) union other) incl elem
  }

  if (true) 1 else false

  override def toString = "{" + left + elem + right + "}"
}

并制作相同包装的一部分

package pk

object genric {

  val h10 = new nonEmpty(90, new empty, new empty)
  val h9 = new empty()
  var h11 = new cons(h10, nil)
  list.f(h11, h9)
  //   val h9=new nonEmpty(5,new empty,new empty)
}

trait List[+T] {
  def head: T

  def tail: List[T]

  def isEmpty: Boolean

  def prepend[u >: T](elem: u): List[u] = new cons(elem, this)
}

class cons[T](var head: T, val tail: List[T]) extends List[T] {
  def isEmpty = false
}

object nil extends List[Nothing] {
  def isEmpty = true

  def tail = throw new NoSuchElementException

  def head = throw new NoSuchElementException
}

object list {
  def apply[T](a: T, b: T) = new cons(a, new cons(b, nil))

  def apply = nil

  def f(xs: List[nonEmpty], x: empty) = xs prepend x
}

当我使用scala解释器运行它时，它说我的方法中找不到nonEmpty F（）我无法理解为什么它给我错误，虽然我有相同包中的文件

Answer 1

因为Scala解释器从上到下读取文件，所以在使用之前需要确保声明了一个类。因此，在第一个文件中，您需要移动nonEmpty声明并首先读取该文件。

第一档：

abstract class tree {
  def contains(x: Int): Boolean

  def incl(x: Int): tree

  def union(other: tree): tree
}

class nonEmpty(elem: Int, left: tree, right: tree) extends tree {
  def contains(x: Int): Boolean = {
    if (x < elem) left contains x
    else if (x > elem) right contains x
    else true
  }

  def incl(x: Int): tree = {
    if (x < elem) new nonEmpty(elem, left incl x, right)
    else if (x > elem) new nonEmpty(elem, left, right incl x)
    else
      this
  }

  def union(other: tree): tree = {
    ((left union right) union other) incl elem
  }

  if (true) 1 else false

  override def toString = "{" + left + elem + right + "}"
}

class empty extends tree {
  def contains(x: Int): Boolean = false

  def incl(x: Int): tree = new nonEmpty(x, new empty, new empty)

  override def toString = "."

  def union(other: tree): tree = {
    other
  }
}

尽管代码在同一个包中，但在Scala中找不到错误

1 个答案: