Unable to define predicate in Prolog

Question

I have just started learning `Prolog` and so pardon me if this is a bit naive, or rather a lot naive. I am trying to define this predicate ``` | ?- times(M,N,Product) :- Product is M*N. ``` which gives me this error ``` uncaught exception: error(existence_error(procedure,(:-)/2),top_level/0) ``` I am using GNU Prolog. What is the fault here ?

Accepted Answer

As false said, If you want to define a predicate or function during the execution of the interpreter, you must enter the "user" mode of the interpreter, by typing:

```
['user'].
```

After typing your predicates, you'll just need to leave this "zone", as a confirmation to the interpreter that you're finished with the coding, and it can start to compile your predicates to bytecodes -- which you'll be, then, allowed to access through your function names.

To leave the "user" mode simply press `ctrl + d`.

Tested in both swipl and gprolog:

```
SWI-Prolog version 5.10.4
(GNU Prolog) 1.3.0
```

Regards!

Unable to define predicate in Prolog

Solution

Problem