Prolog factorial recursion

Question

I\'m having trouble understanding the following factorial program

fact1(0,Result) :-
    Result is 1.
fact1(N,Result) :-
    N > 0,
    N1 is N-1,
    fac         


        

Answer 1

I would do something like:

fact(0, 1).
fact(N, Result):-
    Next is N - 1,
    fact(Next, Recursion),
    Result is N * Recursion.

And a tail version would be like:

tail_fact(0, 1, 0).         /* when trying to calc factorial of zero */
tail_fact(0, Acc, Res):-    /* Base case of recursion, when reaches zero return Acc */
     Res is Acc.
tail_fact(N, Acc, Res):-    /* calculated value so far always goes to Acc */
     NewAcc is N * Acc,
     NewN is N - 1,
     tail_fact(NewN, NewAcc, Res).

So for you to call the:

non-tail recursive method: fact(3, Result).

tail recursive method: tail_fact(3, 1, Result).

This might help ;)