Here is my quick solution.
( Quick, so, it will fail the unit test, since it does not check the
parameters and throw the expected exception; however, it shows the
example graphics correctly )
Created by Morton G. 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
Place the turtle at [x, y]. The turtle does not draw when it
changes
position.
def xy=(coords)
@xy = coords.dup
end
Set the turtle’s heading to .
def heading=(degrees)
@heading = degrees
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
@pen = false
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
@pen = true
end
Is the pen up?
def pen_up?
!pen_down?
end
Is the pen down?
def pen_down?
@pen
end
Places the turtle at the origin, facing north, with its pen up.
The turtle does not draw when it goes home.
def home
@xy = [0.0, 0.0]
@heading = 0.0
pen_up
end
Homes the turtle and empties out it’s track.
def clear
home
@track = []
end
Turn right through the angle .
def right(degrees)
@heading += degrees
end
Turn left through the angle .
def left(degrees)
right(-degrees)
end
Move forward by turtle steps.
def forward(steps)
x = @xy[0] + steps * cos((90 - @heading) * DEG)
y = @xy[1] + steps * sin((90 - @heading) * DEG)
go([x,y])
end
Move backward by turtle steps.
def back(steps)
forward(-steps)
end
Move to the given point.
def go(pt)
if @pen
if !@track.empty? && @track.last.last == @xy
@track.last << pt.dup
else
@track << [@xy.dup, pt.dup]
end
end
@xy = pt.dup
end
Turn to face the given point.
def toward(pt)
@heading = 90 - acos((pt[0] - @xy[0]) / distance(pt)) / DEG
end
Return the distance between the turtle and the given point.
def distance(pt)
sqrt((@xy[0] - pt[0]) ** 2 + (@xy[1] - pt[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