Syntax-rules Primer for the Merely Eccentric | Hacker News Reader

Syntax-rules Primer for the Merely Eccentric

xs4all.nl

21 pointsfogus7 comments

I've read this and various other scheme macro tutorials and still can't make sense of them. There's still a lot going on in the background with hygenic macros, basic tutorials won't teach you how to write even simple ones on your own.

PLT seems to document them well from the ground up: http://download.plt-scheme.org/doc/html/guide/macros.html

I was in the same boat until I finally read this (chapter 8):

http://www.scheme.com/tspl3/

Scheme may be simple, but scheme macros are not. They go way overboard in trying to protect you from yourself. I'm glad to see Arc moving back in the direction of CL macros, which I think makes it a very interesting alternative to Scheme.

Most Schemes give you define-macro (and gensym), which is the same as CL macros. Bigloo, Chicken, and some others even have hygienic macros off by default due to the overhead, and recommend that you use define-macro whenever possible.

I usually use a mixture of both. define-macro for when I'm just trying to kill some repetition without an obvious functional composition solution, and define-syntax for when I'm laying serious groundwork functionality.

> Bigloo, Chicken, and some others even have hygienic macros off by default due to the overhead, and recommend that you use define-macro whenever possible.

Not anymore for Chicken! Chicken 4.0 switched to `syntax-rules' and explicit renaming macros.

Edit: those who like traditional macros might also like explicit renaming ones [1,2], since they're very similar.

[1] http://www.gnu.org/software/mit-scheme/documentation/mit-sch...

[2] http://chicken.wiki.br/explicit-renaming-macros

oops, you're right. nice!

I honestly can't decide if the news that many scheme implementations encourage you to not follow the standard refutes or supports my point.

Either way, good to know.

...gets back to work hacking in SBCL.

Joe Marshall's essay is very good, but if you want to start from something simpler consider http://www.phyast.pitt.edu/~micheles/scheme/TheAdventuresofa...

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