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The Case Against the word "Macro"
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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...
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...so imagine if
John McCarthy
(the inventor of Lisp) had used the word "add" instead of "cons"
to connect items to lists: It would make it really difficult
to explain how consing works.
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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:
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- 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" returns
about 1,150,000 hits. A Google search for
"(spel OR spels) programming -lisp -scheme" returns only
about 28,400. Even worse when you consider that the search
"(macro OR macros) programming (lisp OR scheme)" only
returns a measly 395,000!
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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.
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If you have a library or are a Lisp implementation author,
please drop everything you are doing right now
and add the following line to your library:
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(defmacro defspel (&rest rest) `(defmacro ,@rest))
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There, problem solved!
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;-)
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-- Conrad Barski, M.D.
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