Arithmetic evaluation and testing is performed by predicates that take arithmetic expressions as arguments. An arithmetic expression is a term built from numbers, variables, and functors that represent arithmetic functions. These expressions are evaluated to yield an arithmetic result, which may be either an integer or a float; the type is determined by the rules described below.
At the time of evaluation, each variable in an arithmetic expression must be bound to a number or another arithmetic expression. If the expression is not sufficiently bound or if it is bound to terms of the wrong type then Prolog raises exceptions of the appropriate type (see ref-ere-hex). Some arithmetic operations can also detect overflows. They also raise exceptions. e.g. Division by zero results in a domain error being raised.
Only certain functors are permitted in arithmetic expressions. These are listed below, together with a description of their arithmetic meanings. For the rest of the section, X and Y are considered to be arithmetic expressions.