A FOR statement has the form:
FOR id := first TO last BY step DO S END
where id is an identifier, first and last are
ordinal expressions with the same base type,
step is an integer-valued expression, and S is a statement.
"BY step" is optional; if omitted, step defaults to
1.
The identifier id denotes a readonly variable whose scope is S and whose type is the common base type of first and last.
If id is an integer, the statement steps id through the values first, first+step, first+2*step, ..., stopping when the value of id passes last. S executes once for each value; if the sequence of values is empty, S never executes. The expressions first, last, and step are evaluated once, before the loop is entered. If step is negative, the loop iterates downward.
The case in which id is an element of an enumeration is similar. In either case, the semantics are defined precisely by the following rewriting, in which T is the type of id and in which i, done, and delta stand for variables that do not occur in the FOR statement:
VAR
i := ORD(first); done := ORD(last); delta := step;
BEGIN
IF delta >= 0 THEN
WHILE i <= done DO
WITH id = VAL(i, T) DO S END; INC(i, delta)
END
ELSE
WHILE i >= done DO
WITH id = VAL(i, T) DO S END; INC(i, delta)
END
END
END
If the upper bound of the loop is LAST(INTEGER) or LAST(LONGINT), it should be rewritten as a WHILE loop to avoid overflow.