INC and DEC statements have the form:
INC(v, n)
DEC(v, n)
where v designates a variable of an ordinal type
and n is an optional integer-valued argument. If omitted,
n defaults to 1. The statements increment and decrement
v by n, respectively.
The statements are equivalent to:
WITH x = v DO x := VAL(ORD(x) + n, T) END
WITH x = v DO x := VAL(ORD(x) - n, T) END
where T is the type of v and x stands for
a variable that does not appear in n. As a
consequence, the statements check for range errors.
In unsafe modules, INC and DEC are extended to ADDRESS.