來自Scala編程的螺旋示例似乎不起作用

Question

我正在學習Scala，並且正在使用Martin Odersky寫的《在Scala中編程》一書。 當我嘗試第10章中的示例時，它並沒有產生預期的結果。 我試圖在這里和那里稍微修改一下代碼，但是沒有運氣。 誰能告訴我我要去哪里錯了？

import Element.elem

object Spiral {
  val space = elem(" ")
  val corner = elem("+")

  def spiral(nEdges: Int, direction: Int): Element = {
    if(nEdges == 1)
      corner
    else {
      val sp = spiral(nEdges - 1, (direction + 3) % 4)
      //println("H: " + sp.height + " W: " + sp.width + " D " + direction)
      def verticalBar = elem('|', 1, sp.height - 1) //updated based on google errata which was otherwise def verticalBar = elem('|', 1, sp.height)
      def horizantalBar = elem('-', sp.width, 1)
      if(direction == 0)
        (corner beside horizantalBar) above (sp beside space)
      else if (direction == 1)
        (sp) beside (corner above verticalBar) //updated based on google errata which was otherwise (sp above space) beside (corner above verticalBar)
      else if (direction == 2)
        (space beside sp) above (horizantalBar beside corner)
      else
        (verticalBar above corner) beside (sp) //updated based on google errata which was otherwise (verticalBar above corner) beside (space above sp)
    }
  }

  //Not working as expected, need to debug and fix
  def main (args: Array[String]) {
    val nSides = args(0).toInt
    println(spiral(nSides, 0))
  }
}

這是使用14作為參數運行時的預期結果

+-------------
|             
| +---------+ 
| |         | 
| | +-----+ | 
| | |     | | 
| | | +-+ | | 
| | | + | | | 
| | |   | | | 
| | +---+ | | 
| |       | | 
| +-------+ | 
|           | 
+-----------+ 

我得到什么

+-------------
| +---------+

Answer 1

我認為代碼應該是

def spiral(nEdges: Int, direction: Int): Element = {
if (nEdges == 1)
  elem("+")
else {
  val sp = spiral(nEdges - 1, (direction + 3) % 4)
  def verticalBar = elem('|', 1, sp.height)
  def horizontalBar = elem('-', sp.width, 1)
  if (direction == 0)
    (corner beside horizontalBar) above (sp beside space)
  else if (direction == 1)
    (sp above space) beside (corner above verticalBar)
  else if (direction == 2)
    (space beside sp) above (horizontalBar beside corner)
  else
    (verticalBar above corner) beside (space above sp)
 }
}

我還沒有運行，請您檢查一下是否可行？

Answer 2

您可能沒有更新Element類，而是在方法上方和旁邊添加了widen和heightn函數調用。