I remember being sorta-vaguely interested in it a long while ago, but never tried it. Now that I've learned Arc, all I can see is that the examples would be half as short (or shorter!) with macros. :P
If I were to strictly translate the example on their home page, it might look like this:
Okay, not quite half as short, but even so. From what I can tell, traits seems to be an interesting way to combine objects together, according to a contract. Not saying this is "The Way", but it might be interesting to write a traits.arc library to play around with it.
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Also, apparently traits were invented in Self... which also invented prototypes (!):