I have a function square which I would like to display a matrix like this:
XXX (newline) XXX (newline) XXX My result is false after first line is printed. Why? How are variables transmitted in Prolog and how are the lines executed(order)?
line(Rez,X) :- Rez>=1 , write(X) , line(Rez-1,X). square(N,X) :- Rez = N,line(Rez,X),nl,N>1,square(N-1,X). There are several issue with your code. Notably, you're writing recursive predicate definitions without base cases. Another issue is that Prolog is not a functional language. When you write e.g. line(Rez-1,X), Prolog is not going to evaluate Rez-1 as an arithmetic expression. For Prolog, Rez-1 is just a '-'/2 compound term, i.e. a term with name - and two arguments. You will need to write something like NextRez is Rez-1, line(NextRez,X). The is/2 standard built-in predicate evaluates its second argument (as an arithmetic expression) and unifies the resulting with the first argument.
