I am new to Prolog. Trying to run this code but gives - ERROR: Undefined procedure: teaches / 2 (DWIM cannot fix target)

These are the facts that I wrote

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).

      

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 teaches std with id 20110303

it gives this error. I have tested it for all kinds 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)

      

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2 answers


Getting error

Using SWI-PROLOG I get the same error if I use editor

to enter facts and rules and then in Prolog interpreter

runs a query for example.

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

      

Download using help

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 query

?- teaches(D,20110303).

      



I am getting correct result

D = ahmed ;
false.

      

Using the listing

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

.

If I use the listing to check the predicate teaches

before loading it with help, 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 predicates consult

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

      

and check with listing, I see predicate

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

      

+3


source


  • Let's say your file name is question.pl.

If you are on Mac or Ubuntu

  1. Just open a terminal

  2. go to the directory where you saved the file

  3. Enter this command [question].

  4. Now run your query (D, 20110303).



If you are in windows it is very easy just to double click on the saved file, it will open a terminal, you can call your request from that terminal.

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