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:
/(10, 2, 5.0).
/(10, -2.0, -5.0).
/(9, 12, 3_4). (with set_flag(prefer_rationals, on))
Fail:
/(1, 2, 1.0).
/(5, 2, r).
/(6, 2, 3).
Error:
/(A, 2, 6.0). (Error 4).
/(2, 0, Result). (Error 20).
/(4 + 2, 2, 12). (Error 24).