Re: indomain/2 gives type error in version 5.5 (not before!)

From: Sebastian Sardina <>
Date: Mon 02 Dec 2002 04:48:10 AM GMT
Message-Id: <>
On Fri, 2002-11-29 at 09:21, Warwick Harvey wrote:
> Hi Sebastian,
> On Thu, Nov 28, 2002 at 11:46:32PM -0500, Sebastian Sardina wrote:
> > I have fd and fd_search loaded:
> > 
> > [eclipse 35]: X :: [red, blue, green], indomain(X, random).
> > type error in indomain(_248{[blue, green, red]}, random)
> > Abort
> Yes, this used to work.
> > [eclipse 36]: X :: [red, blue, green], indomain(X, split).
> > type error in indomain(_248{[blue, green, red]}, split)
> This never worked.

yes you are right here. My mistake. random worked but split never did.

> The fd_search library was never intended to work for symbolic domains; the
> fact that it did work for the random method was purely accidental (the
> original author of the library was very surprised to hear that it did).
> Since the last release, the fd_search code has become common between it and
> the ic_search library.  In making it generic, some of the error checking and
> reporting was cleaned up.  Some months later we realised that this may have
> inadvertently stopped fd_search from working with symbolic domains, but when
> investigating the impact of this we discovered that only the random method
> had worked previously and that that had been accidental.  In the lead up to
> the 5.5 release we considered trying to restore the functionality to
> maintain complete compatibility, but it wasn't a high priority and it wasn't
> clear how useful the functionality was anyway.  (And if we were going to
> address symbolic domains, it probably should have been done properly, which
> we certainly didn't have time for.)

ok I understand now.

> In any event, it shouldn't be too hard to write your own indomain predicate
> to do what you want.  In particular, you can use ::/2 to retrieve a
> representation of the current domain of a variable, which you can then pass
> to the nth_value/3 predicate provided by fd_search, which returns the Nth
> value in the given domain (though if your domains are symbolic, ::/2 will
> always return a simple list, which you can do with as you like).  Plug in a
> random number (or whatever ordering you like) and "Bob's your uncle" as they
> say...

now I can write something like:

my_random_choice(X) :- ........  < using nth_value/3 and random/1 >

Now here is my big doubt:

	2) how can I make my random-choice procedure to repetitively select
different random values for X without repeating? should
my_random_choice/1 be responsible of doing that or search/6 itself takes
care of this? 

> Once you have this predicate you can of course use it as the choice method
> in a call to search/6; indeed, by providing your own selection and choice
> methods, the variables don't even need to be FD variables: in the past I've
> used fd_search's search/6 to solve problems involving sets.

Yes right they don't even have to be FD variables. But should my
my_random_choice/1 be as good and efficient as the indomain_random
already provided for say integer finite domains? My program uses many
types of variables, only some of them being symbolic. I want to apply
search/6 randomly for every variable but I want a general and still
efficient solution.

> Cheers,
> Warwick


Received on Mon Dec 02 04:57:43 2002

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