Prolog syntax error on format

Question

I am getting a syntax error on my format line and i have no idea why!

magic3(Variables):-
   Variables[A,B,C,D,E,F,G,H,I],
   fd_domain(Variables,1,9),
   fd_all_different(Variables),
   A+B+C #= A+D+G,
   A+B+C #= A+E+I,
   A+B+C #= C+F+I,
   A+B+C #= B+E+H,
   fd_labeling(Variables),
   format("A=~w, B=~w, C=~w~n, D=~w, E=~w, F=~d~w, G=~w, H=~w, I= ~w", Variables).

The code prints

A B C
D E F
G H I

where all rows and columns are equal when added together I can not figure out why I am getting a syntax error.

Answer 1

In several systems you need to put at the beginning of your file/module:

:- use_module(library(clpfd)).

And as a tiny improvement you can introduce the sum S:

S #= A+B+C,
S #= D+E+F, % this too!
S #= G+H+I,
....

And even better, you can now calculate the sum with is (1+2+ ...+9) / 3 = 15. So add S #= 15. There is a nice animation on the Internet for the actual labeling process.

---

Further:

Variables[A,B,...]

should read

Variables = [A,B,...]