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@REPLYADDR Mild Shock <bursejan@gmail.com>
@REPLYTO 2:5075/128 Mild Shock
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@TID: FIDOGATE-5.12-ge4e8b94
Is there any use case for the cycle check? It gives an error more earlier.
If one has a resource quota, one would also get an error only a little bit
later, when the stack is to large and some memory is exhausted.
Here is a sketch of a post mortem analysis, even written in 100%
pure Prolog, which gives an error analysis service:
X is Y :-
catch(eval(Y,X), error(foo, ),
(acyclic term(Y) -> throw(error(bar, )); throw(error(baz, )))).
The single error "foo" produced by the internal eval/2 predicate
is changed into either an error "bar" or an error "baz", to provide the
end-user some more information. Can be also implemented
natively by the builtin is/2, making a cycle test during eval/2
unnecessary, since acyclic term/1 exists. Or is there a danger
that acyclic term/1 crashes? It probably uses less stack than eval/2.
Mild Shock schrieb am Sonntag, 10. September 2023 um 23:45:55 UTC+2:
> Ok there is a big confusion in SWI-Prolog discourse, I was
> mentioning native stack, and people think I was talking
> about native code. Holy cow! Do I speak chinese, or what?
>
> Just look for yourself. Step 1: Go to GNU Prolog GitHub,
> Step 2: Lookup the C function Load Math Expression
> Interesting find, for Dogelog Player on CPython so far:
>
> /* Dogelog Player 1.1.1, CPython */
> ?- X=1+X, Y is X.
> Unknown exception: `maximum recursion depth exceeded`
>
> What does PyPy do? What does JavaScript do? How do we
> handle this exception. Are there more candidates than only (is)/2,
> like for example copy term/2, etc.. This would cover Dogelog
>
> Player. What about formerly Jekejeke Prolog, respectively Java?
> Mild Shock schrieb am Samstag, 9. September 2023 um 22:18:21 UTC+2:
> > The internal call is tail recursive I guess, since the functor is
> > already checked, and a looked up handle, a function pointer,
> > causes the evaluation. Recently GNU Prolog has moved to GitHub,
> >
> > so I can find the source code of GNU Prolog stuff more easily, things
> > like Load Math Expression. But I think the GNU Prolog approach is
> > only feasible, if you dare to rely on the native stack.
> >
> > Concerning the new Java foreign function interface. I switched
> > from handles obtained by method reflection to handles that were
> > populated via functional interfaces. Its an itch faster, and close
> >
> > to SWI-Prolog optimised, but only for JDK 8:
> >
> > /* Jekejeke Prolog, 1.6.3, JDK 8, Functional Interface */
> > ?- time(test).
> > % Time 171 ms, GC 2 ms, Wall 09/09/2023 22:04
> > true.
> >
> > The above uses the native stack like GNU Prolog and no
> > cycle testing nothing. But I guess it burns CPU since it uses
> > two pointers to represent a term. I hope I can soon get rid of that.
> >
> > Another brake could be the varargs array allocation.
> > Mild Shock schrieb am Samstag, 9. September 2023 um 22:17:13 UTC+2:
> > > I started using this test case:
> > >
> > > test :-
> > > between(0,1000000,N),
> > > is exp(1+N/1000000),
> > > fail.
> > > test.
> > >
> > > To test a new Java foreign function interface. I then
> > > observed that SWI-Prolog stack engine causes
> > > a little overhead:
> > >
> > > /* SWI-Prolog, 9.1.14, optimise=false */
> > > ?- time(test).
> > > % 2,000,001 inferences, 0.313 CPU in 0.315 seconds
> > > (99% CPU, 6400003 Lips)
> > > true.
> > >
> > > /* SWI-Prolog, 9.1.14, optimise=true */
> > > ?- time(test).
> > > % 1,000,002 inferences, 0.172 CPU in 0.176 seconds
> > > (98% CPU, 5818193 Lips)
> > > true.
> > >
> > > Intrestingly GNU Prolog doesn`t use a stack engine,
> > > just relies on the native stack. Its quite speedy without
> > > any optimisation:
> > >
> > > /* GNU Prolog 1.5.0 (64 bits) */
> > > ?- test.
> > > (125 ms) yes
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