The Case Against the Word "Macro"
Part of the purpose of writing this tutorial is to experiment with ways that can tackle the difficult subject of true macros in Lisp. Often, when I try to explain the concept of macros to somebody who has only used other languages, I'll get a response like "Oh yeah! There's macros like that in C++, too!". The moment this happens, it becomes very difficult to explain "true macros", because of the semantic load on the word "macro". After all, "true macros" really are a lot like C++ macros, in that they are a way to talk to the compiler with modified code...
...so imagine if John McCarthy had used the word "add" instead of "cons" to connect items to lists: It would make it really difficult to explain how consing works.
Therefore, I decided to experiment with a new term for a macro in this essay: SPEL, which stands for "Semantic Program Enhancement Logic", which is admittedly a bit of a stretch, but the term has many benefits:
- It captures the almost magical power that Lisp macros can have to change the behavior of a Lisp environment.
- The term SPEL can be used in a million different ways to explain programming concepts in elegant ways, using the metaphor of the spell and casting spells.
- The term causes no confusion between true macros and other types of macros.
- The semantic load of the term "spel" is very low. A Google search for "(macro OR macros) programming -lisp -scheme" return 1150000 hits. A Google search for "(spel OR spels) programming -lisp -scheme" return only 28400. Even worse when you consider that the search "(macro OR macros) programming (lisp OR scheme)" only returns a measly 395000!
So I hope, as a Lisper, you'll consider supporting this new term. Naturally, any new memes like this have a very low likelihood of success.
If you are an LFE library author, please drop everything you are doing right now and add the following line to your code:
(defmacro defspel body `(defmacro ,@body))
There, problem solved!
-- Conrad Barski, M.D.