Documentation for method bool-only

Documentation for method bool-only, assembled from the following types:

role Iterator

From Iterator

(Iterator) method bool-only

By default is not implemented, but expected implementation for types that do this role is:

method bool-only(--> Bool:D{ ... }

The method returns True if there are elements that can be generated by this Iterator by, for example, calling pull-one, and False otherwise. Important: it's expected the Iterators that implement this method can produce that answer without exhausting themselves. In other words, it's expected the user of the class will be able to still pull-one after calling this method.