Neat! Now when on the topic, some thoughts on what would be a next level in this, generally: A nice way to deliver generics would be to make it control flow analysis-optimized at the level of the module system/code expander/expanded code. CFA2 might be something, Dimitris Vardoulakis' thesis may tell if it delivers for call/cc, and possibly Matt Might http://matt.might.net/ has something to say on the topic, search for abstract interpreter. (ref<http://brendaneich.com/2010/08/static-analysis-ftw/> ref <http://matt.might.net/articles/implementation-of-kcfa-and-0cfa/>) As long as that works well enough to optimize ~80-95% of uses to ordinary procedure calls you've got a generics system that really delivers for most purposes. Of course without that delivers for lots of purposes too. Feel free to share any reflections. Brgds 2013/4/22 Jason Felice <jason.m.felice@gmail.com>

Clearly, there could be more features and it could be more efficient, but in terms of producing the simplest thing that works for me, I'm really happy with this:

https://gist.github.com/eraserhd/5435505

Usage:

(define-generic (length object))

(add-method (length (vector? v)) (vector-length s)) (add-method (length (string? s)) (string-length s)) (add-method (length (list? l)) (##length l))

(length "hello") => 5 (length '(1 2 3)) => 3 (length '#(a b)) => 2

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