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*To*: address@hidden, address@hidden*Subject*: RE: Demystifying Continuations*From*: Guy Steele - Sun Microsystems Labs <address@hidden>*Date*: Fri, 22 Mar 2002 17:29:01 -0500 (EST)*Cc*: address@hidden*Reply-to*: Guy Steele - Sun Microsystems Labs <address@hidden>*Sender*: address@hidden

From: "David Simmons" <David.Simmons@smallscript.net> Date: Fri, 22 Mar 2002 13:39:37 -0800 ... > But one can define continuations mathematically without resorting to the > kind of explanation you want. > Guy really hit the nail on the head here - as an implementor of a certain > type of language, you're steeped in ideas like reifiable cloneable > contexts, and that's the model that you want to translate continuations > into. Anton, Perhaps I misunderstood his humor. I thought he was alluding to the fact the the terms I used were, in and of themselves, non-trivial concepts. Which in turn meant that my using those terms to explain continuations was perhaps no simpler or easier to understand than "explanations" I had complained about in my original missive. Okay, I need to 'fess up here. Indeed, I had originally intended only this bit of humor about non-trivial concepts. But I did not object when Anton managed to extract a deeper meaning from my jest. ... All in all, I find myself needing to disagree with you. I take the view more of a physicist wanting to know the first principles and build the ideas from there. That gives me much more latitude to explore new ideas and understand what is possible. It is the same approach that has allowed me to build a Smalltalk architecture that was richer than the classic Smalltalk-80 designs that had preceded it. A laudable goal, but let me caution that we, like physicists, should treat with some skepticism the assumption that one can find "*the* first principles". There is always the possibility that one can find two or more stories or explanations, each of which can be explained in terms of the others and which seem equally sinple or low-level, at least for some areas of application. Two simple examples from physics: (a) Which is the more fundamental, the time domain or the frequency domain? Given that they are interconvertible through the Fourier transform, about the best one can say sometimes is that one or the other is more convenient for some purposes. (b) Which is the more fundamental concept, mass or momentum? Think carefully, and be sure to consider both quantum mechanics and general relativity. So for computational science. Which is more fundamental, procedures or data structures? Which is more fundamental, lambda calculus or Turing machines? You can take either as a first principle and then derive the other and show their equivalence. --Guy

**Follow-Ups**:**Re: Demystifying Continuations***From:*Anton van Straaten <anton@appsolutions.com>

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