On Syntax and Macros

From what I have read, it seems that most people have an ultimate Zen moment with Lisp that makes the universe seem to fall into order (or, so says Eric S. Raymond). My journey with Lisp so far hasn’t been like that. Instead, it has been a number of smaller “Aha!” moments. In fact, I just had one today. Maybe my big Zen moment will come later. I guess I’ll just need to keep learning and see where the Lisp journey takes me.

Getting back to the “Aha!” moment, I was reading an article by Andrew Gavin about how he used Lisp in creating games for Naughty Dog. In the article he says that “…C provides series of convenient macros for flow control, arithmetic operations, memory reference, function calling, and structure access.” My first reaction was “No, Andy. You’ve got it all wrong. Those aren’t macros, they are part of the syntax…”

Syntax, in any language, is just a bunch of macros you didn’t need to write.

Then I paused, thought for a minute, and made a realization: if macros are syntax, is the inverse also true? Is syntax just macros? Yes, yes it is. Syntax, in any language, is just a bunch of macros you didn’t need to write. Why? Because all languages are later compiled to something else.

Compilation is a fancy way of saying you transform one language into another, much like macros transform one piece of syntax into another piece of syntax. Not much like; it’s exactly like that. Transforming Lisp to Lisp is not all that different from transforming C to assembly, or Python to bytecode. That is what Andrew ultimately does with his custom Lisp dialect, GOOL: compile Lisp into R3000 assembly code.

So, thanks Andy. Your twenty year old article taught me something fundemental about Lisp and computer science. And the Lisp journey continues.

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