Hi pd,
> > > : (? (factorial @X 120))
> > > -> NIL
> >
> > This is another issue. This Pilog version of factorial cannot do reverse
> > lookup,
> > as it calculate numeric values via Lisp calls.
> ...
> Ok, I suspected that but is there any way to do arithmetic in pilog? My
> understanding is you have to use picolisp for arithmetic
>
> How should be declared factorial primitive to be compatible with reverse
> lookup?
I have not tried. How is it in real Prolog?
To take an example a bit simpler than the factorial function, you could start
with addition as:
(be + (@A @B @C)
(^ @A (- @C @B)) )
(be + (@A @B @C)
(^ @B (- @C @A)) )
(be + (@A @B @C)
(^ @C (+ @A @B)) )
With that, you can do thing like:
: (? (+ 3 4 7))
-> T
: (? (+ 3 4 @X))
@X=7
: (? (+ 3 @X 7))
@X=4
: (? (+ @X 4 7))
@X=3
But where will that end? Should we also handle two or three variables,
generating all combinations of natural numbers? This could surely be done
(similar to what 'append/3' does for lists), but I never saw a need for that.
> May you tell me what syntax is the right one for prolog primitives
> translated to pilog?
>
> prolog pilog
> p(r(b)). (be p (r (b))) -(1)- or
> (be p ((r (b)))) -(2)- or
I would say the first one.
> (be p ((r b))) -(3)-
> p(z(a),b) (be p ((z a) b)) -(1)- or
> (be p ((z (a)) b)) -(2)-
The second one. But I think it does not matter, you can pass any pattern to a
predicate, it is matched in any case.
> what is supposed to mean (be p (r (b))) if anything?
Yeah, there is no "meaning". It is just a pattern.
: (? (p r @X))
@X=(b)
$: (? (p q @X))
-> NIL
: (? (p @A @B))
@A=r @B=(b)
: (? (p @A (@B)))
@A=r @B=b
> May you explain the estructure of a pilog environment (and the use of unify
> function)
The environments are nested association lists, with numbers for the levels and
then the symbols for the values at these levels.
> and how pilog clauses are converted to property lists? what
> kind of unification algorithm uses pilog? maybe in a PilCon session
They are not converted at all. They are stored directly as a list under the 'T'
property of the predicate's symbol. Unification looks them up for each level.
☺/ A!ex
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