Re: pilog - using range

```Alex,

Thank you as always. Very helpful```
```
By the way, I am reading "Programming in Prolog" by Clocksin/Mellish per
the recommendation on the reference page. I have spent a fair amount of
time reading various prolog tutorials and this book is really clicking for
me.  Thanks again for the recommendation.

For the list, I have found these lectures to be really good too:
http://vimeo.com/user8713508/videos . It filled in alot of the "why" that
was left uncovered in many of the tutorials. The book is doing a great job
as well.

Joe

On Nov 22, 2012 2:56 AM, "Alexander Burger" <a...@software-lab.de> wrote:

> Hi Joe,
>
> > (be add1-or-double (@X @Num)
> >   (member @X (1 2 3 4))
> >   (@Ans + 1 (-> @X))
> >   (@Ans2 * 2 (-> @X))
> >   (or ((equal @Num @Ans)) ((equal @Num @Ans2))))
> >
> > (? (add1-or-double @X 4))
> > @X=2 @X=3:
>
> OK
>
>
> > If I try this:
> >
> > (be add1-or-double (@X @Num)
> >   # (member @X (1 2 3 4))
> >   (@X range 1 100)
>
> 'range/3' is a predicate, not a generator. You can use it only for
> range checks like:
>
>    : (? (range (1 . 5) 3))
>    -> T
>    : (? (range (1 . 5) 7))
>    -> NIL
>
> Its main purpose is for database queries, to be used as a filter for
> numeric or date values.
>
>
> Instead, you might consider using 'for/2'
>
>      (for @X 4)
>      (@Ans + 1 (-> @X))
>      (@Ans2 * 2 (-> @X))
>      (or ((equal @Num @Ans)) ((equal @Num @Ans2))) )
>
>
> To generate an unlimited supply of numbers, you could write
>
>    (be number (@N)
>       (@C box 0)
>       (repeat)
>       (@N inc (-> @C)) )
>
>      (number @X)
>      (@Ans + 1 (-> @X))
>      (@Ans2 * 2 (-> @X))
>      (or ((equal @Num @Ans)) ((equal @Num @Ans2))) )
>
> Note, however, that this won't terminate.
>
> ♪♫
> - Alex
> --
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>
```