Result is Number1 / Number2which should be preferred for portability.
If both arguments are integers, then the result is of type float by default (coinciding with ISO-Prolog). This can be changed by switching the global flag 'prefer_rationals' to 'on': the result is then of rational type, and therefore precise. In practice, a better way to enforce a rational result is by explicitly converting one or both arguments to a rational before dividing, e.g. Z is rational(X)/Y.
The following table details the behaviour on zero-division, depending on the argument types. The exact result depends on the result's type ability to represent extreme values.
-3 / 0 -1.0Inf (negative infinity) 0 / 0 arithmetic exception 3 / 0 1.0Inf (positive infinity) -3.0 / 0.0 -1.0Inf (negative infinity) -0.0 / 0.0 arithmetic exception 0.0 / 0.0 arithmetic exception 3.0 / 0.0 1.0Inf (positive infinity) -3.0 / -0.0 1.0Inf (positive infinity) -0.0 / -0.0 arithmetic exception 0.0 / -0.0 arithmetic exception 3.0 / -0.0 -1.0Inf (negative infinity) rational(-3) / rational(0) representation error rational( 0) / rational(0) arithmetic exception rational( 3) / rational(0) representation error breal(-3) / breal(0) -1.0Inf__-1.0Inf (negative infinity) breal( 0) / breal(0) -1.0Inf__1.0Inf (undefined) breal( 3) / breal(0) 1.0Inf__1.0Inf (positive infinity)Dividing infinity by infinity yields the same result as 0/0.
In coroutining mode, if Number1 or Number2 are uninstantiated, the call to //3 is delayed until these variables are instantiated.
Success: Result is 10 / 2. % gives Result = 5.0 Result is 10 / -2.0. % gives Result = -5.0 Result is 9 / 12. % gives Result = 0.75 % with set_flag(prefer_rationals, on): Result is 9 / 12. % gives Result = 3_4 Error: Result is 2/0. % arithmetic exception