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7.3.3 The Outer Subsequent For

The outer subsequent ‘for’ statement does away with the initial setting of the binding variables. If the regular ‘for’ is equivalent to:

    if (set for initial position in data collection) {
	do {
	} while (set for the next position);
    }

the subsequent ‘for’ is:

	do {
	} while (set for the next position);

The braces block is executed once without the binding variables being set, not bound to, and possibly out of the collection being traversed.

Its syntax has a ‘+’ sign following the initial opening parenthesis.

    for (+a in collection) {
    }

    for (+a, b in collection) {
    }

The first binding variable is required. No declarations are allowed by the syntax.

The program:

    integer a, b;

    a = 4;
    b = 2;
    for (+a, b in list(0, 1, 4, 9, 16, 25)) {
	o_form("~x~\n", a, b);
    }

outputs:

4x2
5x25

The outer subsequent ‘for’ statement is defined for every data types combination for which a plain ‘for’ statement is defined, in the direction in which the latter is defined (forward or backward).