Turtles

LogoLife is about turtles. Logo turtles. Logo turtles are special turtles that know how to draw in the sand. They spend long leisurely days on the beach, tanning their shells and soaking up rays with their cheap sunglasses on. Turtles, being the laid back bunch that they are, will only perform a few tricks when it comes to making lines in the sand. In fact, the only tricks that these turtles have up their sleeve are: Turtles can lift their stick (so they make no tracks) or drop their stick (so they make tracks) Turtles can move forward a specific number of steps. Turtles can turn left and right a specific number of degrees. Turtles can change the color of their stick.

That's all a poor turtle can do. But don't let them fool you! They can draw things you won't believe.

In a later chapter we discuss these commands in detail, and describe how you can write your own turtle logo programs.

Turtle Populations

Turtles live in populations, whose size depends upon your preference. However, you need to consider your computing resources when determining your population sizes. More modern computers with fast CPUs and lots of memory can easily work with populations of 100 turtles. Less impressive computers will need to work with sizes under 50 turtles. Finally, there is currently a practical limit to the number of turtles that can be effective displayed on a given screen size. A 1280x1024 monitor can display 120 turtles. Each turtle in the population has its own sand in which to draw.

Each turtle will draw its figure in the sand during its lifetime, or in a single generation. After each turtle draws its figure, they will display them to you, and you will decide which turtles are fit to reproduce for the next generation of turtles.

Once you have selected the most fit turtles, they will reproduce in a fitness proportionate fashion to create a new population of turtles that will replace the older population. That is, the best turtles will be most likely to be selected to reproduce. As with natural genetics, some of the turtles in the new population will be almost exact duplicates of their parents, while others will combine features of their parents to create a new figure.

Generation after generation, you will select the turtles that exhibit the type of drawing behavior that you seek, and the population will evolve over time to create some of the most fascinating figures you have ever seen, and possibly teach you things about the logo programming language you had not considered.