From Newsgroup: comp.lang.prolog

Now this line of code made me both smile and cry:

doge.pl: $(PROG)
$(file >$@,false :- \+true. ?- ['$<'],$(MAIN).)

Why define false so complicated:

false :- \+ true.

Why not define it as follows:

false :- fail.

The stack overflow user by the name false who
institutionalized false/0 as a synonym for fail/0
by way of ISO Prolog Corrigendum 2:

8.15.5.4 Examples
false.
Fails.

https://www.complang.tuwien.ac.at/ulrich/iso-prolog/dtc2#false

Mild Shock schrieb:

Hi,

Well Ulrich Neumerkel is of course the biggest
quack of all as usual:

order of clause can only influence termination properties

This depends on your definition of termination. There is universal termination and (much rarer) existential termination.

In a pure, monotonic program, order of clauses does not even

influence > universal termination. That is, a goal G_0, false will
terminate in

the very same way regardless of the clause order. (For a goal G_0,
false both universal and existential termination are the same.)

https://github.com/mthom/scryer-prolog/discussions/3004#discussioncomment-13704812

Complete idiots, nothing to do with terminations. DCGs
that consume characters do anyway terminate. What is he talking about?

Bye

Mild Shock schrieb:

Woa! This nonsense really made my day:

https://github.com/mthom/scryer-prolog/discussions/3004

It starts with, where somebody "tried" a declarative DCG
using constraint logic programming:

number_tail(0, 0) --> [].
number_tail(Number, DigitsCount) -->
   ("," | ""),
   digit(Digit),
   number_tail(Digits, RestDigitsCount),
   {
     DigitsCount #= RestDigitsCount + 1,
     Number #= Digit * 10 ^ RestDigitsCount + Digits
   }.

He then noticed that its not deterministic. And since
it is not deterministic, clause ordering changes the
result when onced via once/1.

LoL

If DCGs had a cut, one would any way do:

number_tail(Number, DigitsCount) -->
   ("," | ""),
   digit(Digit), !,
   number_tail(Digits, RestDigitsCount),
   {
     DigitsCount #= RestDigitsCount + 1,
     Number #= Digit * 10 ^ RestDigitsCount + Digits
   }.
number_tail(0, 0) --> [].

Push the determinancy into the DCG. Otherwise you have
an explosion of choice points, and a lot of things go
totally wrong.

But the new DCG standard has no cut (!)/2.

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From Newsgroup: comp.lang.prolog

Hi,

Some Prolog systems have only:

true/0
fail/0

Then some other Prolog systems have:

true/0
fail/0
otherwise/0 (synonyme for true/0)
false/0 (synonyme for fail/0)

Why not include otherwise/0 as well in the ISO
core standard, it can be used to make if-then-else
more readable. Like instead of writing:

(X = red -> write('Roses');
X = blue -> write('Violets');
write('Onions')).

One would write:

(X = red -> write('Roses');
X = blue -> write('Violets');
otherwise -> write('Onions')).

Bye

Mild Shock schrieb:

Now this line of code made me both smile and cry:

doge.pl: $(PROG)
    $(file >$@,false :- \+true. ?- ['$<'],$(MAIN).)

Why define false so complicated:

     false :- \+ true.

Why not define it as follows:

     false :- fail.

The stack overflow user by the name false who
institutionalized false/0 as a synonym for fail/0
by way of ISO Prolog Corrigendum 2:

8.15.5.4 Examples
false.
   Fails.

https://www.complang.tuwien.ac.at/ulrich/iso-prolog/dtc2#false

Mild Shock schrieb:

Hi,

Well Ulrich Neumerkel is of course the biggest
quack of all as usual:

order of clause can only influence termination properties

This depends on your definition of termination. There is universal
termination and (much rarer) existential termination.
;
In a pure, monotonic program, order of clauses does not even

influence > universal termination. That is, a goal G_0, false will
terminate in

the very same way regardless of the clause order. (For a goal G_0,
false both universal and existential termination are the same.)

https://github.com/mthom/scryer-prolog/discussions/3004#discussioncomment-13704812


Complete idiots, nothing to do with terminations. DCGs
that consume characters do anyway terminate. What is he talking about?

Bye

Mild Shock schrieb:

Woa! This nonsense really made my day:

https://github.com/mthom/scryer-prolog/discussions/3004

It starts with, where somebody "tried" a declarative DCG
using constraint logic programming:

number_tail(0, 0) --> [].
number_tail(Number, DigitsCount) -->
   ("," | ""),
   digit(Digit),
   number_tail(Digits, RestDigitsCount),
   {
     DigitsCount #= RestDigitsCount + 1,
     Number #= Digit * 10 ^ RestDigitsCount + Digits
   }.

He then noticed that its not deterministic. And since
it is not deterministic, clause ordering changes the
result when onced via once/1.

LoL

If DCGs had a cut, one would any way do:

number_tail(Number, DigitsCount) -->
   ("," | ""),
   digit(Digit), !,
   number_tail(Digits, RestDigitsCount),
   {
     DigitsCount #= RestDigitsCount + 1,
     Number #= Digit * 10 ^ RestDigitsCount + Digits
   }.
number_tail(0, 0) --> [].

Push the determinancy into the DCG. Otherwise you have
an explosion of choice points, and a lot of things go
totally wrong.

But the new DCG standard has no cut (!)/2.

--- Synchronet 3.21a-Linux NewsLink 1.2

From Newsgroup: comp.lang.prolog

Hi,

Thats a nice test case, failed by Trealla Prolog
and Scryer Prolog. Currently working on fixing it
for Dogelog Player and Jekejeke Prolog:

/* SWI-Prolog 9.3.26 */

% ?- member(N,[5,10,15]), time(test3(N)), fail; true.
% % 2,007 inferences, 0.000 CPU in 0.000 seconds (0% CPU, Infinite Lips)
% % 2,012 inferences, 0.000 CPU in 0.000 seconds (0% CPU, Infinite Lips)
% % 2,017 inferences, 0.000 CPU in 0.001 seconds (0% CPU, Infinite Lips)
% true.

/* Trealla Prolog 2.80.4 */

% ?- member(N,[5,10,15]), time(test3(N)), fail; true.
% % Time elapsed 0.001s, 3020 Inferences, 4.741 MLips
% % Time elapsed 0.019s, 3030 Inferences, 0.159 MLips
% % Time elapsed 0.511s, 3040 Inferences, 0.006 MLips
% true.

/* Scryer Prolog 0.9.4-547 */

% ?- member(N,[5,10,15]), time(test3(N)), fail; true.
% % CPU time: 0.002s, 7_120 inferences
% % CPU time: 0.053s, 7_135 inferences
% % CPU time: 1.657s, 7_150 inferences
% true.

The test case:

hydra(0, n) :- !.
hydra(N, s(X,X)) :-
M is N-1,
hydra(M, X).

hydra2(0, _) :- !.
hydra2(N, s(X,X)) :-
M is N-1,
hydra2(M, X).

test3(N) :-
hydra(N,X), hydra2(1,Y),
between(1,1000,_), unify_with_occurs_check(X, Y), fail; true.

Mild Shock schrieb:

Woa! This nonsense really made my day:

https://github.com/mthom/scryer-prolog/discussions/3004

It starts with, where somebody "tried" a declarative DCG
using constraint logic programming:

number_tail(0, 0) --> [].
number_tail(Number, DigitsCount) -->
  ("," | ""),
  digit(Digit),
  number_tail(Digits, RestDigitsCount),
  {
    DigitsCount #= RestDigitsCount + 1,
    Number #= Digit * 10 ^ RestDigitsCount + Digits
  }.

He then noticed that its not deterministic. And since
it is not deterministic, clause ordering changes the
result when onced via once/1.

LoL

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