/*  File: factorial.P
   Author: Ned Okie (et al.)
   Date:   8/99
   Purpose: To illustrate is, recursive definitions, helper functions, 
                and read/write
*/

fac(0,1).          /* By definition (not needed for recursion) */
fac(1,1).          /* Base case for recursion */

fac(M,N) :- M > 1,                     /* Recursive definition */
            M1 is M - 1,
            fac(M1,N1),
            N is M * N1.

facdemo1(X)  :- fac(X,N), write(N).          /* Helper functions */
facdemo2     :- read(X), fac(X,N), write(N).  /* Terminate input with . */

/*********************** end of file factorial.P ************************/