I have an on again, off again love affair with a language called lisp. It is the second oldest high level computer language with only Fortran being older. It is deceptively simple at its core. It wasn’t even meant to be an actual computer language when it was created. It was a notation created by John McCarthy in 1958 to talk about Church’s lambda calculus. Shortly after he published a paper about it, one of his graduate students, Steve Russell, implemented it on a computer.
Lisp distinguishes itself by being comprised of a half a dozen or so primitive functions, out of which the entire rest of the language can be derived. Just because it can, doesn’t mean that it should be, so most modern lisps compile to either machine code or virtual machine byte code. This typically results in a considerable performance boost.
Lisp was heralded as the language of artificial intelligence. That was probably because it had the novel property of homoiconicity. That is to say, the structure of a lisp program can be faithfully and directly represented as a data structure of the language. This gives it the singular ability to manipulate its own code. This was often thought to be one of the necessary if not sufficient capabilities for a machine that could reason about its own operation.
While this was intriguing, the thing that drew me to lisp was the conciseness of expression that it facilitated. Programs that took hundreds of lines to express in other programming languages were often expressed in four or five lines of lisp.
Lisp was also the first dynamic language. It allows the programmer to continue writing code for execution even after the original program has been compiled and run. The distinction seemed important enough to McCarthy that he termed lisp a programming system instead of a programming language.
I have always found lisp an excellent tool for thinking about data, processing, and the interactions between them. Most other programming languages require a great deal of translation from the design to the finished implementation.
And so, I find myself reading and studying a book called How to Design Programs. It is a text on program design that was written using the DrRacket language system, based on the Scheme dialect of lisp. It is interesting to see the ways that the authors approach certain topics. I hope to get the chance to apply their insights to teaching a class using the book as a text.
Sweet dreams, don’t forget to tell the ones you love that you love them, and most important of all, be kind.