PROLOG: “Syntax error: Operator expected” -

i cannot figure out what's problem in code. please me out. error:

error: c:/users/ahmed/downloads/test.pl:2:4: syntax error: operator expected % c:/users/ahmed/downloads/test.pl compiled 0.00 sec, 21 clauses 

here code:

domains disease,indication = symbol patient,name = string  predicates hypothesis(string,disease) symptom(name,indication) response(char) go  clauses go :-     write("what patient's name? "),     readln(patient),     hypothesis(patient,disease),     write(patient,"probably has ",disease,"."),nl.  go :-     write("sorry, don't seem able to"),nl,     write("diagnose disease."),nl.  symptom(patient,fever) :-     write("does ",patient," have fever (y/n) ?"),     response(reply),     reply='y'.  symptom(patient,rash) :-     write("does ",patient," have rash (y/n) ?"),     response(reply),     reply='y'.  symptom(patient,headache) :-     write("does ",patient," have headache (y/n) ?"),     response(reply),     reply='y'.  symptom(patient,runny_nose) :-     write("does ",patient," have runny_nose (y/n) ?"),     response(reply),     reply='y'.  symptom(patient,conjunctivitis) :-     write("does ",patient," have conjunctivitis (y/n) ?"),     response(reply),     reply='y'.  symptom(patient,cough) :-     write("does ",patient," have cough (y/n) ?"),     response(reply),     reply='y'.  symptom(patient,body_ache) :-     write("does ",patient," have body_ache (y/n) ?"),     response(reply),     reply='y'.  symptom(patient,chills) :-     write("does ",patient," have chills (y/n) ?"),     response(reply),     reply='y'.  symptom(patient,sore_throat) :-     write("does ",patient," have sore_throat (y/n) ?"),     response(reply),     reply='y'.  symptom(patient,sneezing) :-     write("does ",patient," have sneezing (y/n) ?"),     response(reply),     reply='y'.  symptom(patient,swollen_glands) :-     write("does ",patient," have 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. 

you're using swi-prolog, follows edinburgh syntax. code looks code visual prolog, follows different syntax rules. need port code edingburgh syntax if want run under swi-prolog. otherwise, can install visual prolog , run code there.