Category: Article

LAMBDA: The Ultimate Imperative

‘LAMBDA: The Ultimate Imperative’ (found here) is a paper that was written in 1976 by Guy Steele and Gerry Sussman. It is fun to read, informative, and accessible to a wide-variety of programmers and interest levels. Here are some interesting bits about the paper (I will leave the detail to the paper, no sense in trying to re-state what Sussman and Steele have already done so well):
(All bits are either copy-and-paste, or summaries directly from the referenced text, along with my comments)

  • Most programming language constructs can be modeled in terms of lambda, letrec, and if. This might seem pretty radical to folks used to so called “big languages” today. It also might offer some insight into the “minimalistic” nature of Scheme.
  • “Applicative order” of evaluation implies “Call-by-value”. In other words, arguments to functions are evaluated before passing control to the function receiving that value.
  • The paper demonstrates how you can conceptually go from a purely functional world, to one of an imperative nature by leverage call-by-value and macros. This is very, very cool.
  • ‘Tail-recursion’ is perhaps the biggest misnomer of the century. It should be called ‘tail-transfer’. After reading this paper, along with ‘LAMBDA: The Ultimate GOTO’, this becomes quite obvious.
  • Lazy evaluation is introduced, and discussed.
  • Be sure to read the conclusion. It contains numerous gems (both overt and covert) about the role of language, the programmer, and the programming language designer.
  • Keep in mind that this paper was written over 32 years ago. When you take into account the functionality that they describe, and the reasons for its importance; you must put as much effort into thinking about the computing landscape in 1976 as you put into wondering why these kinds of features aren’t in “fashionable languages” today (In my opinion, only Lisp is an acceptable Lisp, and additionally, what does that tell you about “fashionable languages”?).

Always act with choice

Always act with choice. The worse possible thing you can do for yourself is to perform actions begrudgingly. This trains your mind that you are no longer free to make decisions for yourself. Doing so undermines the very foundation on which your ego is built. Live free and choose your actions.
Not every choice will be fun, but the important to always remember is that it is indeed, a choice.

The Lambda Papers

The Lambda Papers are a series of seminal works on programming language design and implementation written by Guy Steele and Gerry Sussman.
You may have heard about them because of the very popular Lambda the Ultimate website, or maybe you just heard about them because you are studying Scheme, or are a student of programming history. Whatever the case, they are very much worth reading (you’ll have to trust me on that).
You should start with ‘AIM-353 Lambda:The Ultimate Imperative’ and follow it with ‘AIM-443 Lambda: The Ultimate GOTO’. Both may be found here.

Addressing slow looping

In the comp.lang.lisp post [Slow Loop (alternatives in lisp?)] Francogrex asked how to implement pivot table functionality without it taking forever using inner loops. Folks posted clearly faster solutions along with good advice. By the way, taking forever means 12 hours for inputs of 1 million data points.
I wondered how you might lead someone down the path to understand how to approach solving a problem (this is pre-HTDP). Here is what I came up with, primarily for myself, mostly as a thought exercise.
Continue reading “Addressing slow looping”

wp-syntax-rettke

Out of the box, WP-Syntax colors code using the default GeSHi colors. Per the authors advice in the ‘Advanced Customization’ section of Other Notes, you can configure GeSHi yourself by handling the wp_syntax_init_geshi hook and configuring it programmatically.
Since I wanted to do just that, I decided to publish a generic plugin, called wp-syntax-rettke, for folks who wanted to configure GeSHi following this approach.

ACM SIGPLAN Lisp Pointers

While reading a (now forgotten) comp.lang.lisp post, I saw the publication ACM SIGPLAN Lisp Pointers mentioned. Unfortunately I don’t have access to this part of the digital library (for that you need to be a paying member). Perhaps this is something in to which it is worth looking.
Any time folks are interested in something which is now seen as arcane ought to look into that topics history. With enough research, the air of mysticism is usually lifted enough so that one may start to grow a more accurate perspective on the topic. This is especially relevant for Lisp and programmers today.

Analogies are a bridge

Analogies are often used to introduce folks to new ideas, introducing them not directly, but through comparison and inference. This seems to work well in all areas, including technical. The risk in using them in technical matters, though, is that person will never move past the analogy and into the realm of accurately understanding the subject matter.
For a long time, I very much disliked analogies. Perhaps this was due to bad personal experiences in my study path with them, or alternately, hearing other folks go on and on about how “such and such is just like such and such” when that is simply not the case. In the past year, though, three interesting things have happened.
The first is that I’ve chatted with someone, who is very level headed and takes the time to talk through his point of view, who is a proponent of analogies.
The second is that I’ve taken a much closer look at how people teach, and, they certainly don’t do it by throwing their students into the deep end.
The third is that I visited a foreign country where it was clear to me that it wasn’t just the language, but just about everything, that I didn’t understand. On the trip I had the experience of analogies about “how things work” in the country just keep popping into my head. It was the strangest thing, but it was interesting, too, because I finally realized the role of analogies:
Analogies are a helpful bridge, that you must cross. If you stay there, you will never get to where you really want to be.

On Lisp

During my vacation, I skimmed Paul Graham’s book On Lisp. There were many interesting bits in there:

  • He really tries to “sell the wonder of Lisp”. I’m not sure is possible, though.
  • “Users prefer double edged swords to blunt ones”
  • I think that he loves Scheme, but uses CL for practical reasons.
  • He digs deep into code, heavily visiting macros and even implementing continuations, non-determinism, and an object system
  • He is probably a world-class hacker who will never be recognized for his talent, but instead his success
  • This is probably not a good “first Common Lisp book” as it is very deep stuff

The XO has got too much Sugar

The XO’s default user interface, Sugar, is very interesting. Its goal is to allow for kids to collaborate, and in doing so, enhance their learning. It is a wonderful idea. The only problem is that it leaves them with a computer that has got barely any memory and no swap (XOs haven’t got swap).
I did a little testing tonight, booting the computer cold, connecting to wifi, and then checking the memory with the ‘free’ command. Here is what I found:

Total MB Used MB Free MB
Sugar 232 220 12
FVWM 232 113 118

I suspect that the result of this is that kids have to be extremely diligent about how many programs they are running. In my experience it is pretty easy to bog the thing down to a stop; just hand it to someone used to operating any other computer; they start three programs, and the operating system will out of memory.
This decision must have been made for a good reason, though. It would be interesting to find it out. I won’t pursue that right now. Anyone happen to know?