Prolog Beginner: How to unify with arithmentic comparison operators or how to get a set var to range
- by sixtyfootersdude
I am new to prolog. I need to write an integer adder that will add numbers between 0-9 to other numbers 0-9 and produce a solution 0-18. This is what I want to do:
% sudo code
add(in1, in2, out) :-
in1 < 10,
in2 < 10,
out < 18.
I would like to be able to call it like this:
To Check if it is a valid addition:
?- add(1,2,3).
true
?- add(1,2,4).
false
With one missing variable:
?- add(X,2,3).
1
?- add(1,4,X).
5
With multiple missing variables:
?-add(X,Y,Z).
% Some output that would make sense. Some examples could be:
X=1, Y=1, Z=2 ;
X=2, Y=1, Z=3 ......
I realize that this is probably a pretty simplistic question and it is probably very straightforward. However cording to the prolog tutorial I am using:
"Unlike unification Arithmetic Comparison Operators operators cannot be used to give values to a variable. The can only be evaluated when every term on each side have been instantiated."
