Problem with variables in prolog

     num(N) :- No=N, write(No), nl.

     check(S) :- No==S -> write(Ok) ; write(Not ok).

When i call num(5), it prints 5. However after calling num(5), when i call check(5), it prints Not ok. I think its because of scope of variables..How can i make it work, i mean variable No like a 开发者_JAVA技巧global variable, so that i can check its value in other clauses?

you can use the global variables of swipl or assert/retract

however, using global variables is a bit against the declarative programming paradigm since it violates referential transparency

There's no global variable in Prolog. If you need a variable in all the clauses, pass it as an argument in those clauses. For example, you use:

check(S, N0) :- N0==S -> write('Ok') ; write('Not ok').

and call check(5, 5) or check(S, 5) as you want.