Result is Number1 / Number2
which 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