From: Edward Faulkner <ef@...>
Date: 2005-09-27T22:54:48+09:00
Subject: Re: Fwd: Lisp macros

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On Tue, Sep 27, 2005 at 09:21:07PM +0900, Devin Mullins wrote:
> Crappy example...
>=20
> Help! Is there a Lisper in the house?

Part of the attraction of Lisp macros is that they allow you to keep
the core language very small, and add the features you want with
macros.  For example, as long as you have the lambda operator, you can
define things like "while" and "let" as macros, not keywords.  This is
in fact how many Lisp implementations work, because it keeps the
compiler/interpreter simple.

Another use for macros is to perform some of your computation at
compile time, saving you from ever needing to perform it again at
runtime.

In the general case, macros can be used to rewrite whole programs.
For example, even though Lisp doesn't natively support continuations,
you can build them with macros that rewrite your program into an
explicit continuation-passing style.

Paul Graham's "On Lisp" is available online and contains several
chapters about macros.  It gives many more examples:

http://www.paulgraham.com/onlisptext.html

regards,
Ed

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