Subject: [Fwd: the state of the art of predicate dispatching]
From: Craig Chambers (chambers@cs.washington.edu)
Date: Mon Jul 09 2001 - 10:01:17 PDT
FYI.
Doug Orleans wrote:
>
> Hi folks. I'm looking into predicate dispatching design &
> implementation for my PhD thesis research-- in particular, the
> relationship between predicate dispatch and aspect-oriented
> programming-- and I wanted to see what the current state of the art
> was.
>
> 0. People: Is there anyone else I should add to this discussion?
>
> 1. Publications: As far as I can tell, there are still only two
> published papers on predicate dispatching: "A Unified Theory of
> Dispatch" from ECOOP98, and "Efficient Multiple and Predicate
> Dispatching" from OOPSLA99. Am I missing anything? Aaron, did you
> finish your master's thesis on adding predicate dispatching to
> CLOS? Is it available online?
>
> 2. Code: The GUD implementation is avalable from the Cecil project
> site, but there is no source code. Can this be made available?
> How about the code from Aaron's thesis and Greg's DVML project?
> I've been working on a toy implementation in Scheme, but I'd like
> to compare notes because I'm pretty sure some of my algorithms are
> not the best. In particular, neither of the papers really went
> into enough detail about the predicate implication algorithm-- I am
> currently doing the "brute force" approach, i.e. checking every
> consistent truth assignment for the atoms of (or (not P1) P2),
> which works, but seems pretty ugly.
>
> 3. Functionality: The biggest thing that seems to be missing from
> predicate dispatching as described in the two papers is
> call-next-method/resend. Has anyone thought of an elegant way to
> handle this? I think it boils down to providing a way to select a
> subset of the methods that were applicable to the current set of
> arguments, such that there is another single most specific method
> in this subset. Basically some generalization of Cecil's directed
> resend is what I'm aiming for.
>
> 4. AOP: Has anyone else thought much about the connections between AOP
> and predicate dispatching? The similarities between predicates and
> AspectJ's pointcuts seem significant to me, even down to both
> producing a set of bindings to be used in the method/advice.
> Basically, both systems let you say "when a function is called, and
> condition X is true, do Y". My toy predicate dispatch system has,
> instead of generic functions containing methods, a single global
> set of methods that dispatch on join points, where a join point
> object contains the generic function and the list of arguments.
> Most method predicates just compare the jp's gf to the gf that the
> method "belongs to", but aspectual predicates can make more
> interesting decisions based on the gf (like, testing if the gf is
> in a set). Right now my stumbling block is how to get an aspectual
> predicate to be considered more specific than the predicate for the
> actual method implementing the join point; I think I may make
> "before", "after", and "around" be different types of join points
> from regular join points, so that an aspectual predicate only has
> to be more specific than other aspectual predicates. [Sorry if
> none of this makes sense-- I can post some code examples if you want.]
>
> 5. The future: What does the future hold for predicate dispatching?
> It seems like the Cecil team has switched focus to spreading the
> multiple-dispatch word, i.e. to Java programmers, but I assume
> you've still got some predicate dispatch projects on the back
> burner? Jonathan, will you be incorporating some form of predicate
> dispatching into Proto?
>
> Thanks for reading. I look forward to your responses. If you'd
> rather not be in this discussion, let me know and I'll take you off
> the address list.
>
> --Doug Orleans
> Northeastern University
> dougo@ccs.neu.edu
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