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Any identifier can be declared as an iterator. The syntax to define an iterator is the following:

syntax iterator iter;


syntax iterator iter {init := n ; range := k};

where n and k specify the number of initializers (of the form acc := a) and ranges (of the form x in xs) in iterator application. If the number of initializers or ranges is not specified, then any number is allowed in iterator application.

An application of an iterator iter has the general form

iter (acc1 := a1; ..; accn := an) (x1 in xs1; ..; xk in xsk) {body}

where acci, xi are patterns, ai, xsi are expressions, and body is an expression which can refer to the variables bound by the acci, xi. The braces around body are optional.

The iterator application syntax is equivalent to

iter \{acc1 .. accn x1 .. xk := body} a1 .. an xs1 .. xsk