From: James Edward Gray II <james@...>
Date: 2006-12-08T23:00:10+09:00
Subject: Fwd: Please Forward: Ruby Quiz Submission

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Begin forwarded message:

> From: "C=E9dric Finance" <pticedric@gmail.com>
> Date: December 8, 2006 7:49:08 AM CST
> To: "submission@rubyquiz.com" <submission@rubyquiz.com>
> Subject: Please Forward: Ruby Quiz Submission
>
> Hello,
>
>      Here is my solution for the turtle quizz.
>      track is an array a broken lines in which the last point of
> each one is different from the first point of the next one.
>
> C=E9dric

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#  Created by Morton Goldberg on November 02, 2006.
#  Modified on November 14, 2006
#  turtle.rb

# An implementation of Turtle Procedure Notation (TPN) as described in
# H. Abelson & A. diSessa, "Turtle Geometry", MIT Press, 1981.
# 
# Turtles navigate by traditional geographic coordinates: X-axis pointing
# east, Y-axis pointing north, and angles measured clockwise from the
# Y-axis (north) in degrees.

class Turtle
   include Math # turtles understand math methods
   DEG = Math::PI / 180.0

   attr_accessor :track
   alias run instance_eval

   def initialize
	clear
   end

   attr_reader :xy, :heading

   # Check if argument pt is a point
   def __check_point(pt)
      raise ArgumentError unless pt.kind_of? Array
      raise ArgumentError unless pt[0].kind_of? Numeric
      raise ArgumentError unless pt[1].kind_of? Numeric
   end

   def __update_track(new)
      if pen_down?
         if @track[-1] == @xy
            @track[-1] << new
	 else
	    @track << [@xy, new]
         end
      end
   end

   # Place the turtle at [x, y]. The turtle does not draw when it changes
   # position.
   def xy=(coords)
      __check_point coords
      @xy = coords
   end

   # Set the turtle's heading to <degrees>.
   def heading=(degrees)
	raise ArgumentError unless degrees.kind_of? Numeric
	@heading = degrees % 360
   end

   # Raise the turtle's pen. If the pen is up, the turtle will not draw;
   # i.e., it will cease to lay a track until a pen_down command is given.
   def pen_up
	@status = :up
   end

   # Lower the turtle's pen. If the pen is down, the turtle will draw;
   # i.e., it will lay a track until a pen_up command is given.
   def pen_down
	@status = :down
   end

   # Is the pen up?
   def pen_up?
	@status == :up
   end

   # Is the pen down?
   def pen_down?
	@status == :down
   end

   # Places the turtle at the origin, facing north, with its pen up.
   # The turtle does not draw when it goes home.
   def home
	@heading = 0.0;
	@xy = [0.0, 0.0]
	@status = :up
   end

   # Homes the turtle and empties out it's track.
   def clear
	home
	@track = []
   end

   # Turn right through the angle <degrees>.
   def right(degrees)
	self.heading += degrees
   end

   # Turn left through the angle <degrees>.
   def left(degrees)
	self.heading -= degrees
   end

   # Move forward by <steps> turtle steps.
   def forward(steps)
      raise ArgumentError unless steps.kind_of? Numeric
      new = [ @xy[0] + steps * Math.sin(@heading*DEG ) ,
              @xy[1] + steps * Math.cos(@heading*DEG) ]
      __update_track new
      @xy = new
   end

   # Move backward by <steps> turtle steps.
   def back(steps)
	forward(-steps)
   end

   # Move to the given point.
   def go(pt)
      __check_point pt
      __update_track pt
      @xy = pt
   end

   # Turn to face the given point.
   def toward(pt)
      __check_point pt
      self.heading = Math.atan((pt[0]-@xy[0])/(pt[1]-@xy[1]))/DEG
   end

   # Return the distance between the turtle and the given point.
   def distance(pt)
      __check_point pt
      Math.sqrt((pt[0]-@xy[0])**2+(pt[1]-@xy[1])**2)
   end

   # Traditional abbreviations for turtle commands.
   alias fd forward
   alias bk back
   alias rt right
   alias lt left
   alias pu pen_up
   alias pd pen_down
   alias pu? pen_up?
   alias pd? pen_down?
   alias set_h heading=
   alias set_xy xy=
   alias face toward
   alias dist distance
end

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