expand method

Expands each element of this [Iterable]into zero or more elements.

Iterable expand(
Iterable f(E element)
)

Expands each element of this [Iterable]into zero or more elements.

The resulting Iterable runs through the elements returned by [f] for each element of this, in iteration order.

The returned [Iterable] is lazy, and calls [f] for each element of this every time it's iterated.