Commet for the short-attention-spanners: read this: http://blog.racket-lang.org/2011/04/writing-syntax-case-macros.html
5 hours ago, Markku Rontu wrote: > This tutorial helped me to understand some basics of macros. For > example how to generate code with them. Now Racket has lots of other > facilities as well but maybe these give you ideas how to ask more > precise questions? > http://hipster.home.xs4all.nl/lib/scheme/gauche/define-syntax-primer.txt This is *not* a good tutorial for using macros in Racket. When you're dealing with macro systems, the Scheme world has always agreed that having hygienic macros is a good idea, but there was no agreement on anything more low-level than `syntax-rules', and different implementations use different systems. As a result of only `syntax-rules' being in the report, it became somewhat popular out of necessity for people who want to write portable code. But the bottom line is that this is really not a good way to write macros -- you're basically confining yourself to a rewrite system which is very hard to deal with, and after a lot of teeth grinding you eventually implement enough rewrites to have a lambda-calculus like thing that you can use to do a bit more programming. (And this is where this tutorial takes you.) If you're working in Racket, it makes much more sense to really use its syntax system rather than stick to those tricks. > On the topic of macros, I find it a bit confusing that to > metaprogram in Racket, I must use such a different language of > macros (with syntax-rules et al.), instead of being able to > manipulate common data structures with plain old Racket functions. This confusion (as have been pointed in other replies) is a direct result of reading that tutorial and thinking that you must use only `syntax-rules'... > The approach in Clojure, that the code is just a common data > structure, easily manipulatable with Clojure code, is > intriguing. What I must do with syntax-rules et al. brings me > memories of template metaprogramming in C++, where I had to twist my > mind in order to be able to do the most simple of things. Writing > regular tree manipulation in Racket is easy, but manipulating the > syntax tree with the macro support is not because of this "language > switch". ...and with that limitation in place, this criticism is absolutely correct. It's a nice description for why you should really *not* limit yourself to only `syntax-rules'. Read that blog post: it shows you how you can use plain racket code to write macros -- and it introduces some of the tools that make it easy to deal with syntax values. -- ((lambda (x) (x x)) (lambda (x) (x x))) Eli Barzilay: http://barzilay.org/ Maze is Life! _________________________________________________ For list-related administrative tasks: http://lists.racket-lang.org/listinfo/users
