Hello, Dušan!

> This is not Prolog, it is a Prolog with CLP extension over integers.

as well as Haskell has a lot of extensions. I mentioned CLP as solver but modern Prologs is not ISO only and has a lot of solvers (CHR, different CLP, FuzzyLogic, Tabulating, etc). Actually CLP(x) in included in most modern implementations.

Hello PY/Paul,

 

You are using misleading arguments!

 

This is not Prolog, it is a Prolog with CLP extension over integers.

 

>

> factorial(0, 1).

> factorial(N, F) :-

> N #> 0,

> N1 #= N - 1,

> F #= N * F1,

> factorial(N1, F1).

>

> I can call it: factorial(5, X) => X=120.

> But also: factorial(X, 120) => X=5.

>

 

Pure Prolog is:

 

factorial(0, 1) :- !.

factorial(N, F) :-

NN is N - 1,

factorial(NN, FF),

F is FF * N.

 

which is a function, not a relation, as you write.

 

 

 

Dušan Kolář