Metacircular Trigger Warning

"Trigger warnings" are cautionary alerts that something may be coming up that could cause problems for certain members of an audience, perhaps due to past traumatic experiences. In the classic MIT Computer Science textbook Structure and Interpretation of Computer Programs, available now online, there's an interesting trigger warning during one of the original lectures as given by coauthor Gerry Sussman in July 1986. Standing at the blackboard, Professor Sussman notes in lecture 7A:

... So we're going to see an amazing thing today. We're going to see, on the blackboard, the universal machine. And we'll see that among other things, it's extremely simple.

Now, we're getting very close to the real spirit in the computer at this point. So I have to show a certain amount of reverence and respect, so I'm going to wear a suit jacket for the only time that you'll ever see me wear a suit jacket here. And I think I'm also going to put on an appropriate hat for the occasion. Now, this is a lecture which I have to warn you — let's see, normally, people under 40 and who don't have several children are advised to be careful. If they're really worried, they should leave. Because there's a certain amount of mysticism that will appear here which may be disturbing and cause trouble in your minds.

Well in any case, let's see, I wish to write for you the evaluator for Lisp. Now the evaluator isn't very complicated. It's very much like all the programs we've seen already. That's the amazing part of it. ...

... and it is truly amazing: a program that can evaluate itself, pick itself up by its bootstraps and fly away — a Universal Machine, a snake that forever eats its own tail ...

(cf. Meta-circular evaluator, KeyToTheTreasure (2004-04-23), ...) - ^z - 2015-11-05