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Re: Non-determinant foreign predicate

From: Daniel Diaz
Subject: Re: Non-determinant foreign predicate
Date: Mon, 7 Jan 2013 09:11:54 +0100


Le 5 janv. 2013 à 17:07, mcculloch <address@hidden> a écrit :
> I am writing an interface to mongoDB from GNU Prolog using mongo's C driver. 
> I want a non-determinant predicate to access query data via a C routine that
> takes care of its own pointer called a cursor.  The cursor structure is
> defined outside of the foreign function, so I don't need to call
> Pl_Get_Choice_Buffer or Pl_Get_Choice_Counter.  I will call
> Pl_No_More_Choice, but only when the cursor has reached the end of its data.
> Does anyone know how prolog knows that a foreign predicate is
> non-determinate.  Is it the "choice_size" in the foreign command, or is it
> something else?  I need my foreign predicate to be non-determinate even if
> it doesn't need to use a buffer.

You are right, you need to specify the choice_size option for a non-det foreign 
predicate. You can pass 0 if you don't need an explicit storage.


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