CODEWITHSUNDEEP
swi-prologvisual-prolog
user3386191
user3386191

Reputation: 1

How can I fix Prolog Syntax error: Operator expected error?

PROLOG: “Syntax error: Operator expected”
ERROR: c:/users/zulfekarali/Desktop/KBS/kbs.pl:2:3: Syntax error: Operator expected
% c:/Users/ZulfekarAli/Desktop/KBS/kbs.pl compiled 0.00 sec, 27 clauses

--------

domains
    disease,indication = symbol
    Patient,name = string

predicates
    hypothesis(string,disease)
    symptom(name,indication)
    response(char)
    go
clauses
    go :-
        write("What is the patient's name? "),
        readln(Patient),
        hypothesis(Patient,Disease),
        write(Patient,"probably has ",Disease,"."),nl.

    go :-
        write("Sorry, I don't seem to be able to"),nl,
        write("diagnose the disease."),nl.

    symptom(Patient,fever) :-
        write("Does ",Patient," have a fever (y/n) ?"),
        response(Reply),
        Reply='y'.

    symptom(Patient,rash) :-
        write("Does ",Patient," have a rash (y/n) ?"),
        response(Reply),
        Reply='y'.

    symptom(Patient,headache) :-
        write("Does ",Patient," have a headache (y/n) ?"),
        response(Reply),
        Reply='y'.

    symptom(Patient,runny_nose) :-
        write("Does ",Patient," have a runny_nose (y/n) ?"),
        response(Reply),
        Reply='y'.

    symptom(Patient,conjunctivitis) :-
        write("Does ",Patient," have a conjunctivitis (y/n) ?"),
        response(Reply),
        Reply='y'.

    symptom(Patient,cough) :-
        write("Does ",Patient," have a cough (y/n) ?"),
        response(Reply),
        Reply='y'.

    symptom(Patient,body_ache) :-
        write("Does ",Patient," have a body_ache (y/n) ?"),
        response(Reply),
        Reply='y'.

    symptom(Patient,chills) :-
        write("Does ",Patient," have a chills (y/n) ?"),
        response(Reply),
        Reply='y'.

    symptom(Patient,sore_throat) :-
        write("Does ",Patient," have a sore_throat (y/n) ?"),
        response(Reply),
        Reply='y'.

    symptom(Patient,sneezing) :-
        write("Does ",Patient," have a sneezing (y/n) ?"),
        response(Reply),
        Reply='y'.

    symptom(Patient,swollen_glands) :-
        write("Does ",Patient," have a swollen_glands (y/n) ?"),
        response(Reply),
        Reply='y'.

    hypothesis(Patient,measles) :-
        symptom(Patient,fever),
        symptom(Patient,cough),
        symptom(Patient,conjunctivitis),
        symptom(Patient,runny_nose),
        symptom(Patient,rash).

    hypothesis(Patient,german_measles) :-
        symptom(Patient,fever),
        symptom(Patient,headache),
        symptom(Patient,runny_nose),
        symptom(Patient,rash).

    hypothesis(Patient,flu) :-
        symptom(Patient,fever),
        symptom(Patient,headache),
        symptom(Patient,body_ache),
        symptom(Patient,conjunctivitis),
        symptom(Patient,chills),
        symptom(Patient,sore_throat),
        symptom(Patient,runny_nose),
        symptom(Patient,cough).    

    hypothesis(Patient,common_cold) :-
        symptom(Patient,headache),
        symptom(Patient,sneezing),
        symptom(Patient,sore_throat),
        symptom(Patient,runny_nose),
        symptom(Patient,chills).

    hypothesis(Patient,mumps) :-
        symptom(Patient,fever),
        symptom(Patient,swollen_glands).

    hypothesis(Patient,chicken_pox) :-
        symptom(Patient,fever),
        symptom(Patient,chills),
        symptom(Patient,body_ache),
        symptom(Patient,rash).

    hypothesis(Patient,measles) :-
        symptom(Patient,cough),
        symptom(Patient,sneezing),
        symptom(Patient,runny_nose).

    response(Reply) :-
        readchar(Reply),
        write(Reply),nl.

Upvotes: 0

Views: 5957

Answers (2)

Wouter Beek
Wouter Beek

Reputation: 3407

The code you provide is invalid SWI-Prolog code because of several reasons.

1

The already observed occurrence of non-commented free text before the first occurrence of go:-.

2

The predicates write/[3,4] do not exist in SWI-Prolog.

3

Predicate readln/1 exists in library readln. Even though this module is auto-loaded, it is better to make the dependency explicit using declaration :- use_module(library(readln)). at the top of the file.

More importantly, readln/1 returns lists, but hypothesis/2 and symptom/2 seem to anticipate non-list input.

4

There is a mismatch between the elements in readln/1 which are atoms and the other arguments of write/[3,4] that are strings.

Upvotes: 1

Javier
Javier

Reputation: 831

domains
    disease,indication = symbol
    Patient,name = string

predicates
    hypothesis(string,disease)
    symptom(name,indication)
    response(char)
    go
clauses

I think this piece of code should be commented with % symbol in order to fix the syntax error.

And here, as another issue, you might want to cut (!) at the final of the predicate, otherwise Prolog because of backtracking will try the second go when it succeeds this first one.

go :-
    write("What is the patient's name? "),
    readln(Patient),
    hypothesis(Patient,Disease),
    write(Patient,"probably has ",Disease,"."),nl,!.

Upvotes: 1

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