Iterator

An Iterator value is something that can be used to get a sequence of other values by abstracting the actual way used to calculate them.

Getting iterators

An Iterator value can't be created directly, but it can be create from another value by using the iterator operator >:

let a = [1, 2, 3];

let aIt = >a;

If the value we are using the iterator operator on doesn't provide an iterator, the operator will return null:

io.print(>5); // null

Advancing iterators

The next operator * can be used on Iterator values to get the current value and advance the Iterator to the next value.

The next operator returns an object with two keys: value and done. The value property will contain the current value and the done property will be true if there are no more values left for the iterator to generate:

let a = [1, 2];

let aIt = >a;

let v = *aIt;

io.print(v.value, v.done);

v = *aIt;

io.print(v.value, v.done);

v = *aIt;

io.print(v.value, v.done);

Outputs:

1 false

2 false

null true

note

The use of a separate done value allows for Iterators to also return null values without any ambiguity.

Cycling

Iterator values can be used in conjunction with the for in loop to iterate over the values of a finite Iterator:

let a = [1, 2];

for (let item in a) {

io.print(item);

}

Outputs:

1

2