
The Art of the Propagator (2008) [pdf] - davexunit
http://groups.csail.mit.edu/mac/users/gjs/6.945/readings/art.pdf
======
JadeNB
In Higher-order Perl
([http://hop.perl.plover.com/book](http://hop.perl.plover.com/book)), MJD
introduces local propagation networks, and says of them:

> If you’ve ever seen a discussion of local propagation networks before,
> you’ve probably seen the Fahrenheit-Celsius converter example. There’s a
> good reason for this: It’s one of the few examples for which local
> propagation actually works.

([http://hop.perl.plover.com/book/pdf/09DeclarativeProgramming...](http://hop.perl.plover.com/book/pdf/09DeclarativeProgramming.pdf),
logical p. 487, Section 9.2.2). Since I value his opinion, that makes me
sceptical about developments in propagators; but, then again, Sussman
certainly knows what he's talking about! Was MJD's opinion never true, or is
it no longer true, or does it remain true (but presumably with caveats)? EDIT:
Or, alternately, am I misunderstanding the relationship between this paper and
the networks that MJD discusses?

~~~
davexunit
I don't know enough about propagator systems to know if there is a mismatch
between what MJD and GJS are talking about. I do know that GJS's propagator
model does more than the simple Farenheit-Celsius conversion problems (this
example is actually in SICP chapter 3, but not in this paper), such as
tracking the reasons why cells hold the data they do and withstanding logical
contradictions.

