Implementation of Langton's Ant - WLHN Sept '14

Langton.scala

object Langton extends App {

  // TODO - make infinite vectors...
  type Grid = Vector[Vector[Boolean]]

  case class Ant(pos: (Int, Int), direction: Symbol) {

    // If current position is white (false), move right 1 square
    // If position is black (true), move left
    def move(grid: Grid): Ant = {
      (grid(pos._1)(pos._2), direction) match {
        case (true, 'N) => Ant((pos._1 - 1, pos._2), 'W)
        case (true, 'W) => Ant((pos._1, pos._2 + 1), 'S)
        case (true, 'E) => Ant((pos._1, pos._2 - 1), 'N)
        case (true, 'S) => Ant((pos._1 + 1, pos._2), 'E)
        case (false, 'N) => Ant((pos._1 + 1, pos._2), 'E)
        case (false, 'W) => Ant((pos._1, pos._2 - 1), 'N)
        case (false, 'E) => Ant((pos._1, pos._2 + 1), 'S)
        case (false, 'S) => Ant((pos._1 - 1, pos._2), 'W)
      }
    }
  }

  // Flip a single point on the grid
  def changeGrid(grid: Grid, pos: (Int, Int)): Grid = {
    // Should probably map this but its good enough...
    (for (x <- 0 until grid.length) yield {
      if (x != pos._1) grid(x) 
      else {
        (for (y <- 0 until grid(x).length) yield {
          if (y != pos._2) grid(x)(y)
          else !grid(x)(y)
        }).toVector
      }
    }).toVector
  }
  
  //  move the ant, change the grid based on the old position
  def step(ant: Ant, grid: Grid): (Ant, Grid) = (ant.move(grid), changeGrid(grid, ant.pos))

  // Vector[Vector[Boolean]] -> pretty
  def display(grid: Grid, ant: Ant): Unit = {
    val printable = (for (x <- 0 until grid.length) yield {
      if (x != ant.pos._1) grid(x).map(c => if (c) "xx" else "__")
      else {
        (for (y <- 0 until grid(x).length) yield {
          if (y != ant.pos._2) {if (grid(x)(y)) "xx" else "__"}
          else "**"
        }).toVector
      }
    }).toVector
    
    for (x <- printable) {
      for (y <- x) Console.print(y)
      Console.println()
    }
    
    Console.println(ant)
  }

  // Take one step, print it, sleep, and do it again
  def play (ant: Ant, grid: Grid, steps: Int): (Ant, Grid) = {
    if (steps != 0) {
      val (a, b) = step(ant, grid)
      display(b, a)
      Thread.sleep(100) //So we can see movement flickering in the console...
      play(a, b, steps - 1)
    } else {
      (ant, grid)
    }
  }
  
  // Create a 40x40 grid, and start off with all cells white
  val grid: Grid = {
    (for (x <- 0 to 39) yield {
      (for (y <- 0 to 39) yield false).toVector
    }).toVector
  }
  // Put the ant in the middle, pointing North
  val ant = Ant((20, 20), 'N)

  // Go 3000 steps
  val (a,b) = play(ant, grid, 3000)
  display(b, a)
}

Output.txt

Output after 100 iterations:
________________________________________________________________________________
________________________________________________________________________________
________________________________________________________________________________
________________________________________________________________________________
________________________________________________________________________________
________________________________________________________________________________
________________________________________________________________________________
________________________________________________________________________________
________________________________________________________________________________
________________________________________________________________________________
________________________________________________________________________________
________________________________________________________________________________
________________________________________________________________________________
________________________________________________________________________________
________________________________________________________________________________
________________________________________________________________________________
________________________________________________________________________________
__________________________________________xxxx__________________________________
________________________________________xx____xx________________________________
__________________________________xx__xxxx______xx______________________________
________________________________xx__**__xxxxxx__xx______________________________
________________________________xx____________xx________________________________
__________________________________xx____xx______________________________________
____________________________________xxxx________________________________________
________________________________________________________________________________
________________________________________________________________________________
________________________________________________________________________________
________________________________________________________________________________
________________________________________________________________________________
________________________________________________________________________________
________________________________________________________________________________
________________________________________________________________________________
________________________________________________________________________________
________________________________________________________________________________
________________________________________________________________________________
________________________________________________________________________________
________________________________________________________________________________
________________________________________________________________________________
________________________________________________________________________________
________________________________________________________________________________
Ant((20,18),'N)


Output after 3000 iterations:
________________________________________________________________________________
________________________________________________________________________________
________________________________________________________________________________
________________________________________________________________________________
________________________________________________________________________________
________________________________________________________________________________
________________________________________________________________________________
________________________________________________________________________________
________________________________________________________________________________
________________________________________________________________________________
________________________________________________________________________________
________________________________________________________________________________
____________________________xxxx________________________________________________
__________________________xxxxxxxx____xxxx______________________________________
________________xxxx____xx__xxxx__xxxxxx**______________________________________
______________xxxx______xxxxxxxx__xx__xx__xxxxxxxx______________________________
____________xx__xxxx__xx__xx__xxxx______xx____xx__xx____________________________
____________xxxxxxxx__xxxxxx____xxxxxx______xx__xxxxxx__________________________
__________________xxxxxxxxxxxxxxxxxxxx__xx__xx____xxxx__________________________
__________xx____xx______xxxx______xxxx____xxxxxx__xx____________________________
________xx__xx____xx__xx__xx__xx______xxxxxxxx__xx______________________________
________xx________________xxxxxxxxxx__xxxxxxxx__________________________________
__________xx____xx__xxxxxxxx________xxxxxxxxxx____xx____________________________
__________xx________xx____________xx__xxxxxxxx______xx__________________________
__________xxxxxx______xx______xxxx__xxxx________xx__xx__________________________
__________xxxxxx__xxxxxx__xxxxxx____xxxx__xx____xxxx____________________________
__________xx______xxxxxxxx______xx__xx____xx__xxxx______________________________
__________xx______xx______xx____xxxx__xx________________________________________
__________xx______xx__xx______xxxxxx________xxxx________________________________
__________xx________xx__xx________xxxx________xx________________________________
__________xx____xxxxxx__xxxx____xx____xxxxxx____xxxx____________________________
__________xxxx__xxxx__________xxxx____xx__xx____xx__xx__________________________
__________xxxxxx______________xx__xxxx____________xx__xx________________________
____________xx____xxxx____xx____xxxx__xxxxxx__xx__xx__xx________________________
______________xxxx__xx________xxxxxx____________xx____xx________________________
__________________xx______xx__xx____xxxxxxxx____xxxx__xx________________________
____________xx__xx________xx__________xx__xxxxxxxxxxxx__________________________
____________xxxxxx________________________xx____xxxx____________________________
______________xx____________xxxx________xx______________________________________
________________xxxxxxxxxxxx____xxxxxxxx________________________________________
Ant((14,20),'S)