Below in code, the representation of a expert system to give response to a pattern of problems in a device (in this case, a mobile one), with the result being the probable cause of the issues, but as you may have seen in the title, this throw a especific error:
go :- catch(Problem),
print("Your problem is probably a"),
print(Problem),
print("Issue"),
nl.
input(Question) :-
write('You have problems such as the follwing:'),
write(Question),
write('?'),
read(output),
nl,
(( output == yes; output == y)
->
assert(yes(Question));
assert(no(Question)), fail).
:- dynamic yes/3, no/1.
verify(Problem):-
(yes(Problem)
-> true;
(no(Problem)
->
fail;
input(Problem))).
undo :- retract(yes(_)),fail.
undo :- retract(no(_)),fail.
undo.
grasp(low_battery) :- low_battery,!.
grasp(software_problem) :- software_problem,!.
grasp(hardware_problem) :- low_battery,!.
%grasp(virus_or_memory_issue) :- virus_or_memory_issue,!.
low_battery :-
verify(phone_not_recharged),
verify(charger_not_working).
software_problem :-
verify(device_turns_on_but_crashes),
verify(some_program_dont_work),
verify(more_than_one_program_crashes_after_awhile),
verify(some_programs_are_not_updated_or_deprecated).
%hardware_problem :-
%verify(device_dont_turn_on),
%verify(device_warmth_frequently),
%verify(screen_exhibits_atipical_visual_patters),
%verify(problems_began_or_intensified_after_fall_or_any_damage).
As a result, the given console is as follows:
ERROR: Unknown procedure: catch/1
ERROR: However, there are definitions for:
ERROR: catch/3
ERROR:
ERROR: In:
ERROR: [11] catch(_4812)
ERROR: [10] go at c:/users/victo/onedrive/documentos/prolog/sistema_especialista.pl:1
ERROR: [9] toplevel_call(user:user:go) at c:/program files/swipl/boot/toplevel.pl:1158
Exception: (11) [user] catch(_4356) ?
Searching for material I've found very little on such matter, and other algoritms I've found were quite not like this one. Any help would be very welcome.
I have a problem with zebra puzzle.
rightOf(A,B,(B,A,_,_,_)).
rightOf(A,B,(_,B,A,_,_)).
rightOf(A,B,(_,_,B,A,_)).
rightOf(A,B,(_,_,_,B,A)).
middleHouse(A,(_,_,A,_,_)).
firstHouse(A,(A,_,_,_,_)).
nextTo(A,B,(A,B,_,_,_)).
nextTo(A,B,(_,A,B,_,_)).
nextTo(A,B,(_,_,A,B,_)).
nextTo(A,B,(_,_,_,A,B)).
nextTo(A,B,(B,A,_,_,_)).
nextTo(A,B,(_,B,A,_,_)).
nextTo(A,B,(_,_,B,A,_)).
nextTo(A,B,(_,_,_,B,A)).
house[Nationality,Pet,Sport,Drinks,Colour].
zebra_owner(Owner) :-
houses(Houses),
exists(house(Owner,zebra,_,_,_), Houses).
length(5,Houses),
exists(house(british,_,_,_,red),Houses),
exists(house(spanish,dog,_,_,_),Houses),
exists(house(_,_,_,coffe,green),Houses),
exists(house(ukrainian,_,_,tea,_),Houses),
rightOf(house(_,_,_,_,green),house(_,_,_,_,ivory),Houses),
exists(house(_,snail,tennis,_,_),Houses),
exists(house(_,_,chess,_,yellow),Houses),
middleHouse(house(_,_,_,mlik,_),Houses),
firstHouse(house(norwegian,_,_,_,_),Houses),
nextTo(house(_,_,rugby,_,_),house(_,fox,_,_,_),Houses),
nextTo(house(_,_,chess,_,_),house(_,horse,_,_,_),Houses),
exists(house(_,_,volleyball,orangejuice,_),Houses),
exists(house(japanese,_,_,_,_),Houses),
nextTo(house(norwegian,_,_,_,_),house(_,_,_,_,blue),Houses),
nextTo(house(_,_,_,tea,_),house(_,_,_,milo,_),Houses),
exists(house(zebra_owner,zebra,_,_,_),Houses).
Under
house[Nationality,Pet,Smokes,Drinks,Colour].
I see the error: Singleton variables: house[Nationality,Pet,Smokes,Drinks,Colour].
And when I write ?- zebra_owner(Owner)
I see the error: procedure 'houses(A)' does not exist. Reachable from:zebra_owner(A).`
You cannot write
house[Nationality,Pet,Sport,Drinks,Colour].
that's non-existent syntax.
To express that predicate house/1 is valid for list [Nationality,Pet,Sport,Drinks,Colour], write:
house([Nationality,Pet,Sport,Drinks,Colour]).
You also must pay attention to predicate naming: houses/1 is not house/1. Predicate houses/1 is defined nowhere (the error message is wrong, it should really say predicate houses/1 is undeclared).
Snippets of my code are shown below. After doing a lot of cumbersome tracing, I have reached a point where I think it's the external modules which are the source of my problem, as the findall in links_of_actor never gets called, but links_of_actor itself gets called. I would be very grateful to anyone who can help and can clarify/add more of my code to this question if needed.
find_identity(A) :-
all_actor_links(ALs),
find_identity(ALs,[],A).
find_identity([a(A,_)],_,A).
find_identity(ALs,Ms,A) :-
agent_ask_oracle(oscar,o(1),link,L),
( memberchk(L,Ms) -> find_identity(ALs,Ms,A)
; otherwise -> purge_actors(ALs,L,NewALs),
find_identity(NewALs,[L|Ms],A)
).
links_of_actor(A,Ls) :-
actor(A),
wp(A,WT),
findall(L,wt_link(WT,L),Ls1),
findall(L,link(L),Ls2),
intersection(Ls1,Ls2,Ls).
actor_links(A,a(A,Ls)) :-
links_of_actor(A,Ls).
all_actor_links(ALs) :-
findall(A,actor(A),As),
maplist(actor_links,As,ALs).
----------------------------------------------------- Support Functions ---------------------------------------------------
% wp(Q,WT) <- issue query Q to Wikipedia and return the page in wikitext format
wp(Q,WT):-
wp_cache(Q,WT),!.
wp(Q,WT):-
wp_query2URL(Q,URL),
http_get(URL,R,[]),
atom_json_term(R,RR,[]),
wt_get(RR,WT0),
( atomic_list_concat1(_L,'#REDIRECT',WT0) -> wt_link(WT0,QQ),wp(QQ,WT)
; otherwise -> WT=WT0
),
assert(wp_cache(Q,WT)).
------------------------------------------------------------ Edit ----------------------------------------------------------------
After using the guitracer that is available with prolog, I have found that the program fails at http_get(URL,R,[]) in the wp(Q,WT) predicate. However, I am still not sure as to why this isn't working - Could it be possibly because of my internet?
To clarify, the predicate actor is defined in my file: actor('Billy Bob Thornton'). etc. and so are the links : link('Barack Obama')..
Using these definitions, the error can be localized by adding a # in front of those goals that have to succeed.
...
wp(Q,WT):-
#wp_query2URL(Q,URL),
#http_get(URL,R,[]),
#atom_json_term(R,RR,[]),
#wt_get(RR,WT0),
...
Well, did you try to see if the URL you gave to http_open is actually valid? You can always test from the top-level if you can http_open an URL:
?- use_module(library(http/http_client)).
true.
?- http_open("stackoverflow.com", R, []).
R = % a lot of stuff
I want to load rdf url from this rule:
getActorFilms(Actor_Name,Films):-
my_replace(Actor_Name, ' ', '_', Correct_Syntax_Of_Actor_Name),
string_concat('http://dbpedia.org/data/',Correct_Syntax_Of_Actor_Name, URL_TO_LOAD),
string_concat(URL_TO_LOAD,'.rdf',RDF_URL),
rdf_load(RDF_URL),
rdf(Films, 'http://dbpedia.org/ontology/starring', Object)
.
when the input is e.g. for an example 'Hugh Jackman'
it tells the error:
ERROR: [Thread pdt_console_client_0_Default Process] source_sink `http://dbpedia.org/data/Hugh_Jackman.rdf' does not exist
I'm really concerned about the ` character between http and source_sink
I think it should be '
although the url is correct, so what to do with that error?
You should pass an atom to rdf_load, not a string. This behavior (the misleading error message, not accepting a string) is probably a bug.
This works for me:
?- use_module(library('semweb/rdf_db')).
true.
?- use_module(library('semweb/rdf_http_plugin')).
true.
?- rdf_load('http://dbpedia.org/data/Hugh_Jackman.rdf').
% Parsed "http://dbpedia.org/data/Hugh_Jackman.rdf" in 0.02 sec; 371 triples
true.
?- string_to_atom(S, 'http://dbpedia.org/data/Hugh_Jackman.rdf'), rdf_load(S).
ERROR: source_sink `http://dbpedia.org/data/Hugh_Jackman.rdf' does not exist
I hope this solves your problem.
I'd like to print a message and stop the evaluation of the predicate. How do I do that?
Take a look at this link where the catch/3 and throw/1 mechanisms in Prolog are described.
It is possible to throw an exception or handle an exception using this mechanism.
The example (given on the site) is:
p:- true.
p:- throw(b).
q:- catch(p, B, write('hellop')), r(c).
r(X) :- throw(X).
Then the call:
?- catch(p, X, (write('error from p'), nl)).
will illustrate the ecxeption handling.
I played with a few other examples which I found. This might be usefull.
p :- throw(b).
r(X) :- throw(X).
q:- catch(p, B, format('Output1: Error from throwing p')), r(B).
catch(throw(exit(1)), exit(X), format('Output: `w', [X])).
Output: 1
1 is thrown to catcher 'exit(X)' and recovered by format('Output: ~w', [X])),
catch(p, C, format('hellop')).
Output: hellop
p throws 'b' which is recovered by writing 'hellop'
catch(q, C, format('Output2, Recovering q: helloq ')).
Output1: Error from throwing p
Output2, Recovering q: helloq
Ben
The stderr stream is aliased to user_error (see https://www.swi-prolog.org/pldoc/man?section=streamalias )
You can write a term (like a string) to a stream using write/2.
You can stop the program using halt.
For example:
% Happy case. Comes first, uses ! to avoid taking the alternative branch
foo(X) :- bar(X, Y), baz(Y), !.
% Fallback branch, in case the above failed. Writes a message and halts.
foo(X) :-
write(user_error, "Couldn't foo"),
halt.