I'm new to Prolog. Trying to run this code but gives - ERROR: Undefined procedure: teaches/2 (DWIM could not correct goal)

Question

These are the facts I have written

instructor(ahmed,mohammed, cs101,01).
instructor(sara,salah,cs101,02).
instructor(maryam,faisal,cs101,03).
instructor(ali,hassan,cs311,01).

enrolled(201110202,huda,issa,cs101,01).
enrolled(20110303,mona,amer,cs101,01).
enrolled(20115566,amal,omar,cs101,01).
enrolled(20118899,ahmed,hassan,cs101,01).

The rules

teaches(D,S):-
   instructor(D,_,C,Z),
   enrolled(S,_,_,C,Z).

classmate(s1,s2,C):-
  enrolled(s1,_,_,C,Z),
   enrolled(s2,_,_,C,Z).

But when I run a query that who teaches std with id 20110303, it gives this error. I have checked it for all kind of errors. It is syntactically and logically correct, but still says undefined procedure

?- debug.
   true.

[debug]  ?-  teaches(D,20110303).
ERROR: Undefined procedure: teaches/2 (DWIM could not correct goal)

Answer 1

Getting the error

Using SWI-PROLOG I get the same error if I use an editor to enter the facts and rules then in the Prolog interpreter run the query, e.g.

ERROR: Undefined procedure: teaches/2 (DWIM could not correct goal)

Loading with consult

Now my facts and rules are in a file named

C:/Users/Eric/Documents/Prolog/soQuestion_4.pl

and if in the interpreter I use consult

?- consult("C:/Users/Eric/Documents/Prolog/soQuestion_4.pl").

then run the query

?- teaches(D,20110303).

I get the correct result

D = ahmed ;
false.

Using listing

One way to check if a predicate is loaded is to use listing.

If I use listing to check the predicate teaches before loading it with consult I get:

?- listing(teaches).
ERROR: prolog_stack([frame(12,call(system:throw/1),throw(error(existence_error(procedure,teaches),context(toplevel,'DWIM could not correct goal')))),frame(11,clause(<clause>(000000000518AD30),62),'$dwim':dwim_existence_error(error,user:teaches)),frame(8,clause(<clause>(0000000005008E40),24),prolog_listing:listing(user:teaches)),frame(7,clause(<clause>(0000000005154870),3),'$toplevel':toplevel_call(user:listing(teaches)))]): procedure `teaches' does not exist (DWIM could not correct goal)

then if I load the predicates with consult

?- consult("C:/Users/Eric/Documents/Prolog/soQuestion_4.pl").
true.

and check with listing I see the predicate

?- listing(teaches).
teaches(A, B) :-
        instructor(A, _, C, D),
        enrolled(B, _, _, C, D).

Answer 2

Let say, Your file name is question.pl. If you are in Mac or Ubuntu

1. Just open your terminal
2. goto the directory you saved your file
3. Enter this command [question].
4. Now run your query teaches(D,20110303).

If you are in windows its very much easy just double click on your saved file it will open terminal you can call your query from that terminal.