Re: [eclipse-clp-users] var vs. free

On 25/01/2011 10:31, Ulrich Scholz wrote:
> Dear Joachim,
>
> thanks for pointing out the difference between var and free.  I'll try to
> keep it in mind.
>
> However, the code my example is based on seems to be a case of a valid use
> of free/1: After the call, the first argument is a solver variable.  If
> called with a free, unattributed variable, a new solver variable is created.
> Otherwise, this step is skipped.

I am not sure from what you wrote if you are dealing with the case where 
an attributed variable is not a solver variable. Normally you would need 
to turn such variables into solver variables as well.

If your 'solver' is a library solver (such as ic), then you probably 
should test if the first argument is a variable or not (with var/1),
and then if a variable is a solver variable (is_solver_var/1 for ic) or 
not, so that a non-solver variable can be turned into a solver variable.

If you are developing your own solver, using your own attribute to do 
so, you can use free/1 to decide if you need to create an attributed 
variable. If this is what you are doing, then I assume you have a clause 
after the clause with free/1 to catch the case where you need to convert 
an existing attributed variable into your solver variable
(as shown in the documentation for free/1 Joachim pointed to).

Cheers,

Kish

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