[erlang-questions] Constraint satisfaction problems

Robert Virding <>
Tue Nov 4 11:48:16 CET 2008

2008/11/4 Jesper Eskilson <>

> On Fri, Oct 31, 2008 at 8:55 AM, Imre Palik <> wrote:
> > During playing with project Euler I solved a few constraint satisfaction
> problems with erlang.  But whenever I code a solution, I have a really
> awkward feeling, that it should be possible to do better, but I don't know
> how.
> >
> > I tend to code a backtracking search with constraint propagation before
> every step.  I model the constraint graph with digraph, but then the
> non-functional nature of the digraph package makes backtracking really
> awkward.
> >
> > Is there any better way to solve constraint satisfaction problems?
> > What is the rationale behind those pesky side effects in digraph?
> If you want to solve Project Euler problems using constraints, I'd
> recommend using Prolog instead. GNU Prolog worked very nice for the
> problems I tried.
> Are there any good constraint libraries for Erlang?

There are no constraint libraries that I know of. However, there is Erlog
which is a prolog implemented in Erlang which works quite well. Depending on
the application. As yet it has no built-in constraint handling but that
could be added if a serious request comes along.

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