[jbclements]

I'm afraid I literally laughed out loud at your request for a simple standard algorithm for r5rs macro systems. However, it's a sympathetic laugh. Macro Hygiene is still very hard, principally because (I claim) there's not yet a clean and widely accepted model for it. Matthew Flatt's "sets of scopes" model is (IMNSHO) the current leader. Time will tell whether he or anyone else comes up with a simpler and more widely accepted model. But yes: as an implementor, it "feels" very heavy, and you keep thinking that there must be a simpler solution to this problem (aside from just throwing the problem out and giving up on hygiene and language composability).

[kovrik]

Yeah, you are right. I've already implemented everything from r5rs, but macro system. And I don't know where to start, just can't wrap my head around it.

And people say that Scheme has a very minimalist design and is easy to implement...

[groovy2shoes]

You may find this paper helpful [1]. As noted there, syntax-rules consists really of two different parts: (1) the hygiene-preserving macro expander and (2) the pattern-matching facility. Once you wrap your head around the two pieces, it's actually pretty straightforward to implement them both. It's very common to write some "low-level" macro facility as a stepping-stone to syntax-rules (such as explicit-renaming macros or syntactic closures): the implementation of syntax-rules then becomes a composition of the pattern-matcher and the low-level facility. A tutorial implementation of an appropriate pattern-matcher can be found at [2],[3].

There's lots of good reading to be found at the ReadScheme Library [4]. Most if not all of the references in [1] can be found there.

Tangentially: yeah, syntax-rules kinda flies in the face of the oft-mentioned minimalism of Scheme, but there's a reason for it: at the time syntax-rules was standardized, there was no consensus on which (if any) low-level facility should be standardized (and, really, there still isn't any such consensus). The reason syntax-rules operates as a pattern-template rewriting system rather than as a procedural system is that such a system is able to guarantee that the macros it produces are hygienic in a (comparably) simple and intuitive way. The idea was to standardize on a high-level system so that Scheme could have a standard macro facility, whilst leaving the low-level systems open for further exploration and experimentation. The two main contenders are still, after all these years, syntax-case and syntactic closures: the latter being easier to implement and arguably easier to grok, the former being potentially more powerful (in that an implementation of syntactic closures within syntax-case is known, but not vice-versa (last I checked)).

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[1]: http://mumble.net/~jar/pubs/scheme-of-things/easy-macros.pdf

[2]: http://blog.theincredibleholk.org/blog/2013/02/11/matching-p...

[3]: http://blog.theincredibleholk.org/blog/2013/02/12/patterns-w...

[4]: http://library.readscheme.org/

[kovrik]

Hey, thank you so much for that! Haven't seen some of those papers. Looks promising. Cheers!