Forrest Sheng Bao's Cyberhome

by Forrest Sheng Bao http://fsbao.net

I can't run sicstus Prolog on my department Solaris workstation. That makes me very unhappy at 3 am. So I decide to use gprolog. And the programming can be easier. In gprolog, FD is built-in.

Factorial in gprolog:

factorial(0,1). 

factorial(N,F) :-  
   N>0, 
   N1 is N-1, 
   factorial(N1,F1), 
   F is N * F1.

Summation in gprolog

sum(0,0). 

sum(N,F) :-  
   N>0, 
   N1 is N-1, 
   sum(N1,F1), 
   F is N + F1.

It seems that "is" is also a built-in predicate in swi-prolog.

I just do not understand why there is no pad sign in front of logic operators. This manual http://www.gprolog.org/manual/gprolog.html#htoc321 confuses me.