Re: [eclipse-clp-users] bb_min and C

Hi Bogdan,

This is the second post you have made about using the C interface, and I 
think the first thing to say is that you should avoid using the C (or 
any of the other interfaces to other languages in ECLiPSe) interface to 
write ECLiPSe programs. That's not what the interfaces are designed for, 
i.e. it is not designed for making ECLiPSe a solver library for C (or C++).

The best way to use the interface is to post goals with simple arguments 
from C, and then do most of the work of constructing the required data 
structures etc. in ECLiPSe, and pass back the required results, again in 
simple data structures, back to C. While it is possible to construct 
complex data structures in C, this is quite tedious, and easy to get 
wrong (including being able to construct incorrect data structures which 
could then lead to hard to debug errors).

Your data structures may be relatively simple as ECLiPSe structures, but 
they are already quite complex, and you obviously are having problems 
with them. So the best suggestion I can make is: don't do this in C.

As for your specific problem: you are posting the bb_options as an atom, 
and this is giving you an type error because bb_options should not be an 
atom. This is in actaully a good illustration of why you should not 
write ECLiPSe progrsm in C: The bb_options{...} is a named structure,  a 
short-hand for a bb_options structure, which is expanded by the parser, 
and is designed to hide implementation details like what the exact size 
of bb_options is, and what the various arguments of the structure is 
used for. However, if you are constructing the goal from C, then you 
need to construct the "raw" structure, i.e. do the work of the parser in 
this case, that is, you need to construct the raw bb_options data 
structure, and in your case, put the strategy option you are using in 
the correct argument position.

You can post a goal that does get parsed from C, by posting the goal as 
a string (ec_post_string()). However, in this case, you don't have 
direct access to the arguments in the goal, and in addition, you need to 
worry about the mostly quite subtle differences between string syntax in 
C and ECLiPSe, especially if you have a complicated goal (again, my 
suggestion is to avoid posting complicate goals).

So in summary, write your ECLiPSe program in C, and keep the interface 
to C simple -- don't try to write the ECLiPSe program in C. If you must 
use C to write your constraint program, then I think ECLiPSe is not the 
tool you want, and you would be better off using some C (or C++) library 
that is designed for this.

Cheers,

Kish

On 24/11/2011 17:36, Bogdan Tanasa wrote:
> Hi,
>
>
>
> I am trying to call bb_min from C.
>
> I am doing something like this:
>
>
>
> search = ec_term(ec_did("search", 6),
>
>                              varList,
>
>                              ec_long(0),
>
>                              ec_atom(ec_did("most_constrained", 0)),
>
>                              ec_atom(ec_did("indomain", 0)),
>
>                              ec_atom(ec_did("complete", 0)),
>
>                              ec_nil()
>
>                              );
>
>
>
>                       bb_min = ec_term(ec_did("bb_min", 3),
>
>                              search,
>
>                              objFunc,
>
>                              ec_atom(ec_did("bb_options{strategy:continue}",
> 0)));
>
>                       ec_post_goal(ec_term(ec_did("writeln", 1), bb_min));
>
>                       ec_post_goal(bb_min);
>
>
>
> I get the following error from CLP:
>
>
>
> type error in
>
> bb_min(
>
> search([_49506{[0, 1]}, _49524{[0, 1]}, _49542{[0, 1]}, _49560{[0, 1]}], 0,
> most_constrained, indomain, complete, []), 1.0 * _49506 + 1.0 *  _49524 +
> 1.0 * _49542 + 1.0 * _49560,
>
> 'bb_options{strategy:continue}') in module eclipse
>
>
>
> The problem is passing the bb_options arguments.
>
> Can you please tell me how to fix it?
>
>
>
> Bogdan.
>
>
>
>
>
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