Classic Computer Magazine Archive COMPUTE! ISSUE 34 / MARCH 1983 / PAGE 148


David D. Thornburg, Associate Editor

On Logo And Turtles

Last December I attended the California Math Council meeting at the Asilomar conference center. Although the conference was directed primarily towards educators from Northern California, attendees came from all over the country.

One evening I was giving an informal presentation in a hospitality suite. While the computer was running a graphics demonstration, one teacher came up to me and said, "I didn't know that Logo ran on the Atari 800."

"That's not Logo," I replied. "That's Atari PILOT."

"Oh," said the teacher, "I thought these pictures were made with turtle graphics."

"They were made with turtle graphics," I said. "Turtle graphics doesn't have any specific relationship to any one computer language."

As we talked some more, it became clear that Logo is becoming more and more identified with the turtle. Worse, the turtle is becoming more and more identified with Logo. While the teacher who approached me seemed startled to find that there were turtles outside of Logo, and that Logo could do far more than turtle graphics, I'm sure that this confusion is commonplace among new computer users.

The real tragedy comes when the association of Logo as simply a turtle graphics language becomes a self-fulfilling prophecy. I am content to believe that many Logo users may not want to use the other features of Logo for the first few months. But any language that has just turtle graphics, no matter how sophisticated, user-friendly, or Logo-like it is, is not Logo.

Radio Shack Color Logo

Unfortunately, the superb turtle graphics package developed for the Radio Shack Color Computer (Radio Shack Color Logo) is one example of such a language. Radio Shack Color Logo supports much of what we expect from Logo — extensibility, local variables, recursion, and turtle graphics. However, the only variables that can be used with this language are numbers. There is none of the list processing capability that gives Logo its tremendous power as a symbol manipulation language.

The sad part is that this symbol manipulation capability is often of value in advanced turtle graphics programs! If you doubt this, you can see some striking examples in Abelson and diSessa's Turtle Geometry, or in my new Logo book.

Even with these detractions, I find Radio Shack Color Logo to be a tremendous turtle graphics language. It supports multiple turtles (created with the word HATCH). It has a built-in procedure editor that allows the user to format multi-line statements so they look nice. (Most other Logos require that you just keep typing a line until you are done. For a line of a few hundred characters in length, this can look messy.)

Radio Shack Color Logo runs in a 32K system (using the disk-based version I had last year), and a cartridge version (as of this writing) is expected to run in a 16K computer. This makes Radio Shack Color Logo one of the less expensive Logo-like turtle graphics packages on the market.

Realtime Animation

The language provides the user with several modes. When the computer is turned on, it is in the BREAK mode. To gain access to the turtle immediately, you simply press R to enter the RUN mode. From this mode the turtle can draw pictures using single commands such as FD 50, RT 37, etc. Unfortunately, you cannot enter repeated commands in this mode. For example, you cannot enter REPEAT 4 (FD 30 RT 90) to draw a square. You must use this command inside a procedure instead.

A very nice feature of the RUN mode that has great appeal to young turtle users is the DOODLE mode. To enter this mode from the RUN mode, the user just types the character @. The computer then waits for the user to enter a word that becomes a procedure name. Once this has been entered, the user can draw pictures by pressing the number keys on the keyboard. Each key corresponds to a different command, e.g., CLEAR, HOME, PENUP, PENDOWN, RIGHT 45, LEFT 45, FORWARD 1, FORWARD 10, RIGHT 15, and LEFT 15. Once a picture is completed, the user can redraw it by simply entering the procedure name from the RUN mode.

The EDIT mode allows the user to create his or her own extensions to the language. These can be saved on disk or tape (for the disk-based version), or on tape (for the cartridge version).

This language also supports user-defined turtle shapes and multiple turtles. Unlike TI's Logo, the user-defined multiple turtles can each draw lines and actually rotate as their orientation is changed. The high speed of these turtles makes this language useful for some realtime animation applications.

Overall, I am quite impressed by this language. As a turtle graphics environment, it should be of great use to all owners of the Radio Shack Color Computer. My only criticism is that Radio Shack is calling the language Logo, when it is not Logo at all.

The task of educating the public and the manufacturers is an important one. After all, you wouldn't think you had purchased a car if it didn't have an engine in it. To call a language Logo, one must be able to perform list processing. It would have been much better if Radio Shack had called the language TurtleTalk, or some other catchy name.

But, until the customers come to understand that Logo is far, far more than just a turtle language, we can't be overly critical when a manufacturer makes the same mistake.