Evaluates Expression as an arithmetic expression, and unifies the resulting number with Term.
An expression made up of:
Arithmetic errors (see ref-ari-exc).
| ?- X is 2 * 3 + 4. X = 10 | ?- Y = 32.1, X is Y * Y. X = 1030.41 Y = 32.1 | ?- Arity is 3 * 8, X is 4 + Arity + (3 * Arity * Arity). Arity = 24 X = 1756
| ?- X is 6/0. ! Domain error in argument 2 of is/2 ! expected an integer not equal to 0, but found 0 ! goal: _98 is 6/0
| ?- X is "a". X = 97 | ?- X is 4 * 5, Y is X * 4. X = 20, Y = 80
If a variable in an arithmetic expression is
bound to another arithmetic expression (as opposed to a number) at
runtime then the cost of evaluating that expression is much greater.
It is approximately equal to the cost of
call/1 of an arithmetic