Return an infinite generator; the first item is aValue, the following
items are obtained by passing the previous value to aBlock.
on: aBlock
Return a generator and pass it to aBlock. When #next is sent
to the generator, the block will start execution, and will be
suspended again as soon as #yield: is sent from the block to
the generator.
on: aCollection do: aBlock
Return a generator; for each item of aCollection, evaluate aBlock
passing the generator and the item.