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For a programmer who cut his teeth on FORTRAN, learned BASIC so he could program microcomputers, and gets a kick out of FORTH, LOGO is the proverbial horse-of-a-different-color.
LOGO was developed primarily as graphics and learning language. Although LOGO is a structured language and is capable of utilizing advanced mathematical functions, I don’t know of anyone who actually does such things with the language (I am sure that somewhere someone does, and I will probably hear from him/her after this is printed). What most people do with LOGO is make pretty pictures, and in the process learn the concepts of structured programming.
The heart of LOGO is the “turtle”. The turtle is a little graphic character which is moved around the screen. leaving line behind. By issuing commands to the turtle to turn and move, created on the screen. a picture or pattern is created on the screen. These commands can be issued in an immediate mode (executed immediately upon entering the command) or in a procedural mode. Procedures can be linked with other procedures to make up a program. By altering the background color, as well as the color and shape of the turtle, quite elaborate patterns and pictures can be created.
Unfortunately, the monochrome graphics of the ZX81/TS1000 and its rather limited graphics capabilities severely limit what can be created by a LOGO system on the machine. The “turtle” is simply a black pixel block, and the line drawn is also a series connected pixels. The coarse quality of the resulting patterns are hardly likely to inspire a budding Rembrant or Picasso. Also, the speed of execution is atrocious even by BASIC language standards. Where most compilers or interpreters are created in very fast languages such as Machine Language, Assembler, or C – the creators of LOGO for the ZX81/TS1000 used Sinclair BASIC! The result is long periods spent staring at blank screen while the machine converts LOGO code to BASIC code, and then long periods spent watching a pixel move laboriously across the screen as the BASIC code is converted to machine language and then executed.
All-in-all, LOGO on the ZX81/TS1000 is dud. The local neighborhood kids I use for “market research” soon tired of the program and went back to playing Flight Simulator.
If anyone is interested in the package, it is entitled “TINY LOGO” and was originally published by Computer Magic. Unfortunately, LOGO on a ZX81/TS1000 isn’t very magical. The package originally sold for about $30, but if you want it you can probably find a used copy – cheap.