since I haven't factored out the constraint propagation into a
general module, the core of my code is a lot longer than the Curry version
(about 60 additional lines, though I'm sure one could reduce that;-). the
only negative point I can find about the Curry example is that it isn't
obvious what tricks the FD-constraint solver is using
Curry does not have a constraint solver of its own. It
simply delegates all constraints to the FD solver of SICStus Prolog.
The all_different constraint subsumes the rules that you describe,
depending on the consistency algorithm used. FD solvers implement general
but efficient algorithms that are much more complex than a few simple
rules.
See
http://www.sics.se/sicstus/docs/latest/html/sicstus/Combinatorial-Constraints.html#Combinatorial%20Constraints
for the SICStus FD all_different documentation.
(ie., it would be nice
to have a concise language for expressing propagation techniques, and then
explicitly to apply a strategy to the declarative specification, instead of
the implicit, fixed strategy of the built-in solver).
CHR is meant as a highlevel language for expressing propagation. It
(currently) does not include a strategy language though.
Cheers,
Tom
--
Tom Schrijvers
Department of Computer Science
K.U. Leuven
Celestijnenlaan 200A
B-3001 Heverlee
Belgium
tel: +32 16 327544
e-mail: [EMAIL PROTECTED]
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