Turtles and Logo Expressions
A LogoLife turtle, like its traditional Logo graphics counterpart
is in actuality a graphical cursor. It has a very simple state,
namely a coordinate position, a direction in which it is pointed,
and a pen that is either up (not drawing) or down (drawing).
The turtle's location is quite inconsequential since all of the
turtle's commands operate in a relative fashion, such as move
forward 2 steps. Further, no matter how large the turtle's drawing
becomes, nor how far it may wander from its original starting point,
the figure is scaled and translated so as to be centered within the
computer display.
The direction in which the turtle is facing is again inconsequential
from the turtle's point of view. Everything that the turtle does is
relative to the direction it is currently facing. This is why the
turtle's language only allows for commands like turn right 10 degrees,
and does not allow for commands such as turn to 48 degrees due north.
The one state that the turtle does manage is the state of the pen.
When the pen is down, the turtle is making figures in the sand. When
the pen is up, the turtle still moves, but does not draw anything.
Population Window
The population window displays a generation of turtles' figures.
Each turtle's figure is drawn for you in a small square in the
Population Window. The population window can also display an enlarged
view of any one of the turtles' figures.
The population window is your view of the evolving world of the
LogoLife turtles. In each successive generation, you will be shown
the turtle's figures and will determine which turtles will be involved
in the evolution of the next generation of turtles.