Dan Weinreb’s blog

I’ve been seeing mail and blog postings, particularly from people in the Lisp community, why MIT has switched from using Scheme to Python in the freshman core curriculum for the department of Electrical Engineering and Computer Science.

At the International Lisp Conference, Prof. Gerry Sussman gave a short impromptu talk explaining the new freshman curriculum.  Just to get a second opinion, I later called Prof. Jacob White, one of the designers of the curriculum and lecturers for the core courses.  (Digression: Jacob and I have been close friends since I was six years old!)  He confirmed Gerry’s description.

Asking why they changed languages is, in some sense, the wrong question.

The freshman software engineering course, since 1985, has been based on the book Structure and Interpretation of Computer Programs (known as SICP), which uses Scheme.  The course is now nearly thirty years old.  Engineering has changed quite a lot in thirty years.  Since 1995, Gerry and his co-author Prof. Hal Abelson have advocated changing the freshman curriculum radically, not basing it on SICP.

In 1980, computer engineering was based on starting with clearly-defined things (primitives or small programs) and using them to build larger things that ended up being clearly-defined.  Composition of these fragments was the name of the game.

However, nowadays, a real engineer is given a big software library, with a 300-page manual that’s full of errors.  He’s also given a robot, whose exact behavior is extremely hard to characterize (what happens when a wheel slips?). The engineer must learn to perform scientific experiments to find out how the software and hardware actually work, at least enough to accomplish the job at hand.  Gerry pointed out that we may not like it this way (“because we’re old fogies”), but that’s the way it is, and M.I.T. has to take that into account.

The new approach also has the big advantage that it combines computer science with electrical engineering, whereas the old one taught them as entirely separate disciplines.  This way, students see how they interrelate.  Also, as Jacob points out, some of the same macro-principles apply to both software and hardware, and the students see this illustrated.  There is extensive lab work, making robots and mobile applications.

It just so happens that the robotics substrate software that comes with the system they’re using is programmed in Python.  Similarly, the mobile software environment is based on Python.  (Or, at least, the original plan was to use such a substrate, although it may have changed for various business reasons.)

Changing programming languages was absolutely not a goal of the curriculum change.  It was merely the result of the consequences of various decisions.  We can always discuss how it came to be that the robots and mobile devices are using Python instead of some other language, but that’s not the question being addressed here.  M.I.T. has nothing against Scheme. (And, of course, M.I.T. does teach classic software engineering, later in the curriculum.)

(Here’s another take on this topic.)

Last December, I was invited to be general chair of the International Lisp Conference 2009.  Since then I have done a great deal of work, and it has finally all paid off.  The conference ran from last Sunday to Wednesday, and it went perfectly!  I can hardly believe it.  And we got at least 215 attendees, which was great!  (I had planned for 175; apologies to those of you who didn’t get a tee shirt and a tote bag.)

The only surprise problem was that two of the speakers were not able to show up.  However, we reallocated their time for more lightning talks.  These are five-minute talks on any topic bearing on Lisp.  Three of them were approved by the program committee and are in the proceedings.  The program committee then agreed that we could post a sign-up sheet, and let anybody talk about anything appropriate.  We ended up having about twenty-five of them.  They were almost all great!  We learned about fascinating new open source libraries, fun applications, great anecdotes, and so on.

The lightning talks make the whole conference more participatory, rather than just “we give the talks, and you sit there and listen.”  Although I’m sorry that the two speakers were unable to present their papers, the lightning talks were great.  I recommend that other conference organizers in the future consider allocating plenty of time for such talks.

The Great Macro Debate went just as I had hoped. Lisp’s macros make the Lisp language extensible.  It’s only because of macros that Lisp has stayed sufficiently up-to-date to still be a relevant language after fifty years of life.  And macros are one of Lisp’s most distinguishing features, now that so many Lisp ideas have been adopted by other languages.

Earlier this year, I was having lunch with my former co-worker, Jeremy Brown.  He had been one of the senior engineers on the Polaris project at ITA Software, and we had worked together closely.  (He left to start his own company, Rep Invariant.)  We were talking about the use of Lisp in Polaris, and specifically about Lisp macros.  To my surprise, Jeremy opined that having macros in the language was a net drawback!  Many people have objected to macros, but Jeremy really knows all about macros; he’s a very proficient Lisp programmer, and has seen how we use macros in Polaris.

So I had the idea of having him debate someone about this at the Lisp conference.  Guy Steele, as program chair, took over the idea, and found people to be in the debate.  Pascal Costanza, who is one of the deepest thinkers about Common Lisp these days, was Jeremy’s prime opponent.  Guy Steele himself was Pascal’s “second”, and Dick Gabriel was Jeremy’s.  I moderated.

Jeremy prepared very thoroughly, with slides that presented all of his attacks, and were also very funny.  The debaters both made important real points, and kept the whole thing hilarious.  There was a great deal of contention and disagreement, to the point where audience members, unable to contain themselves, started shouting out questions and comments.  Indeed, I felt the same way myself, and misused my privilege of having a microphone to participate in the debate.  Finally Dick Gabriel said, “OK, Weinreb, enough of this.  SIt down at the table, and I’ll be the moderator!”  I replied, “Oh, thank you!  Now that I’m a panelist, I can say what I want to into this other microphone!” Sadly, we didn’t videotape this, but we all had a great time.

David Moon’s talk about how to do macros for a language with syntax was very innovative, to the point where, in his introduction, Dave said “some of you may think this is mad scientist stuff”!  It’s certainly fascinating, and the people who had worked on Dylan (and therefore grappled with the same problems) were particularly interested and felt that it looked very promising.

Tom Sgouros performed his one-man, one-robot show: “Judy, or, What Is It Like To Be A Robot”.  I had seen this once at ITA (Tom works at ITA) and knew that it was perfect for this audience.  It’s about the concept of intelligent robots, and the nature of consciousness, and it’s also very clever and funny.  Tom did a wonderful job.

I’ve been catching up on my sleep (really).  But now I’m busy again!  This year’s family opera show, The Weaver’s Wedding, is opening tomorrow.  I’ve been involved in the North Cambridge Family Opera company for about ten years.  While the conference was going on, my wife Cheryl was working very long hours of the day and evening getting the set and props finished, teaching the stagehands what to do, and so on.  (As you can imagine, it’s been rather crazy around at home, with both of those things going on at once!)  I hope to blog more about the conference and papers in the future.  In the meantime, I expect some of the attendees will write their own descriptions.

Thanks again to all our sponsors, who made possible the relatively-low registration.  Special thanks to ITA Software, our Platinum sponsor, and to my wonderful boss, Sundar Narasimhan (CTO and Chief Architect of Polaris), for allowing me to take part time off from my work at ITA in order to run the conference.

Thanks very much to everyone who attended!

Registration for the International Lisp Conference, 2009, is now open.

The conference will be from Sunday, March 22 through Wednesday, March 25, at the Stata Center, MIT, Cambridge, MA.

It features:

• Gerald Sussman, Shriram Krishnamurthi, and David Moon as invited speakers
• Five tutorials (no extra charge)
• Fifteen technical papers
• Seven demonstrations
• Lightning talks (you can give you own; first-come, first-served)
• An all-star panel on the future of Lisp
• The Great Macro Debate
• Birds of a feather sessions, and other informal discussions
• Banquet at the Hyatt-Regency, with special entertainment (no extra charge)

Come meet the top Lisp experts and practitioners in the world. Learn how to get the most out of Lisp. Find about about the latest developments from research and industry. The conference is a rare opportunity for face-to-face interaction, sharing knowledge and ideas with the experts of the worldwide Lisp community. Students are especially welcome. Everyone will have a great time!

Here’s where to find all the information.

Sponsored by:

• ITA Software, Inc.
• Franz Inc.
• LispWorks Limited
• Clozure, Inc.
• Ravenbrook Limited

The schedule for the International Lisp Conference has been posted.  Registration will open shortly.

If you have any interesting in giving a short/lightning talk, you’ll be able to sign up for that at the conference.  You might want to let me know, too, but you need not.

A short talk can be on anything bearing on Lisp, Scheme, or related languages.  It need not be on a profound topic or a research project. It can be as simple as:

• Here’s a good application that we wrote in Lisp.
• Here’s a useful Lisp library that you might want to know about.
• Here are some interesting things about my Lisp development tool.
• I have this provocative/outrageous opinion.
• Please give me feedback about this idea.
• Alice and I will debate the following point.

The ideal duration is five minutes, but the talk could be extremely short, or up to about ten minutes.  There’s no Q and A immediately afterwards.  You can meet up with interested people later to continue talking, answer questions, etc.

This is an informative web page about short/lightning talks in general, and this is a longer one with advice.  But all you have to do is talk for a little while, so don’t worry.

I hope you can come to the conference!

The Scalable Game Design project is aimed at getting computer science into middle schools, to get kids interested in information technology through their natural interest in games. A principal software tool of the project is AgentSheets, which lets you make your own simulation games without learning the syntax of a programming language.

If you know a kid in middle school who wants to make his or her own game, or just learn about programming, I recommend that you take a look at this!

The general concept is a bit like some systems you may have seen before, such as the visual programming languages provided with Lego Mindstorms. However, this requires no special hardware, and the specifics look a lot more interesting and flexible to me than anything I’ve seen along these lines.

An example of what you can do is the classic arcade game Frogger (developed by Konami for Sega/Gremlin in 1981). This tutorial shows how to do it in AgentSheets.

There is a three-minute movie showing kids using AgentSheets. It gives a good sense of the kind of game and the level of complexity that AgentSheets is suitable for (although it doesn’t demonstrate programming itself).

You can also read research papers about the project.

To try it out, you can download a free trial version with a ten-day license, for MacOS X or Windows. It costs $120 in single units, less for educators or if you get ten licenses.

As it happens, it’s written in Common Lisp, which is how I came to hear about it. But that doesn’t matter as far as using it is concerned.

The principal investigator is Prof. Alexander Repenning of the University of Colorado. He has worked at Xerox PARC and HP, and he has collaborated with researchers at the Epistemology and Learning Group of the MIT Media Lab, LOGO, and SRI to explore programmable LOGO toys. He has been involved in many other projects as well.

Thanks for telling me about this, Alex!