Re: pl-iterator

On Nov 1, 2007, at 6:11 PM, Magnus Malm wrote:

> Hello
>
> How does the pl-iterator work in the common lisp api? I can't seem  
> to find any info about this in the docs or the sources.

It works like a standard Stella iterator.  I guess I should make sure  
we have this documented somewhere.

Anyway, the Stella iterator API works like this.  There is a test for  
whether elements remain in the iterator, called "next?" [Lisp:   
stella::next?(), C++/Java: nextP()] that advances the iterator and  
reports whether there is an element present or not.  A fresh iterator  
does not yet point to the first element, so it is safe (and required)  
to call next? before accessing elements.  The value is extracted  
using "value" [Lisp: stella::%value, C++/Java value], which can be  
safely read as often as one wishes.

Summary:
     next?     Advances iterator and reports if a new value exists
     value     Gets the current value.  This is an instance variable  
or field.

Sample Common Lisp usage:
(LET* ((ITER (PLI:S-RETRIEVE "all (concept ?c)" STELLA::NULL-STRING  
NULL)))
    (LOOP WHILE (STELLA::NEXT? ITER) DO
       (PRINT (STELLA::%VALUE ITER))))

    [Unfortunately, the Stella functions are not exported from the  
package.  PLI functions are.]

Sample C++ usage:
   { pli::PlIterator* iter = pli::sRetrieve("all (concept ?c)", NULL,  
NULL);

      while (iter->nextP()) {
        std::cout << iter->value << std::eol;
      }
   }

Sample Java usage:
   use edu.isi.powerloom.*;
   { PlIterator iter = PLI.sRetrieve("all (concept ?c)", null, null);

     while (iter.nextP()) {
       System.out.println(iter.value);
     }
   }



You would then use the PowerLoom API functions "get-nth-..." to work  
with the values or tuples returned by the iterator.