In the world of computing, Hal Abelson is a legend: a much-honored educator and an activist for internet freedom. A professor in the electrical engineering and computer science department at MIT, Abelson is a co-author, with Gerald Sussman, of the classic course and textbook Structure and Interpretation of Computer Programs, which advances an analytical approach to programming language that has influenced computer science education worldwide. On a philosophical and political plane, Abelson has been a founder and director of such public interest groups as Creative Commons, the Center for Democracy & Technology, and the Free Software Foundation—organizations that work variously to promote progressive ideals such as the open dissemination of information on the internet, the personal privacy of Web users, and freedom of expression.
About Turtle Geometry
This code is the first "turtle graphics" system. It's the progenitor of the many subsequent turtle graphics programs that derive from Seymour Paper's seminal work in the Logo educational computer language in the late 1960s, and have been widely adopted throughout education computing ever since.
The original Logo turtle was a physical robot that could be driven around via the Logo commands FORWARD, BACK, (turn) LEFT, and (turn) RIGHT -- and small kids could ride on! When I arrived at MIT in 1969, my first job as a grad student research assistant was to create an analogous system on a graphics display.
Logo was implemented on the MIT Artificial Intelligence Lab's PDP10 computer, and our Logo classes were taught in Lexington, which is 12 miles away. The "display turtle" ran on a vector graphics display that designed to run on a minicomputer -- a Data General Supernova -- that connected to the MIT Lab computer via a phone line. The hardware display was designed by AI Lab staff member John Roe, and it was my job to write the software that implemented the display turtle in Data General assembly language. The display turtle was a great success: as soon as we brought it into the classroom, the kids stopped working on their printing-based Logo projects and gathered around the display. You can see a 1971 video of the Lexington class with Logo and the "Roe Display" running the turtle code here. The page at http://logothings.wikispaces.com/ includes this video and others, with comment by Cynthia Solomon, who taught the class.
This particular assembler code is an extended version of the simple display turtle, enhanced by AI Lab member Ron Lebel. It contains code to also control a plotter as well as the "TK display", one of the first bitmap displays, which were created by Tom Knight. The same code also controlled the Logo "music box", a simple music synthesizer that became the basis for an extensive body of work by Jeanne Bamberger.
- Hal Abelson