A "Lazy" list, as described for Perl 6, is a way of not doing the work to find that list element's value unless (until) it is needed. Often times a list can be compactly represented as an iterator. Perl 5 has some special cases for efficiency, but in Perl 6 the concept of "Lazy lists" is general.

My brainstorm is that a "Lazy list" is just a "work list" of pending tasks that may need to get done. Meanwhile, hyperoperators apply an operator to a list, but assume that it is side-effect free so it can do them in parallel implicitly. But, the iterator and the hyperoperator are just two extremes of a continuum of guarantees and flexibility of how a "work list" can be processed.

It's been touted that hyperoperators are an example of making threading available as a deeper part of the language, not requiring explicit low-level thread operations to acheive. I think that the Lazy list is likewise, but in fact serves as a better exemplar of how to use it for background activities because you can put general and arbitrary work in your work list.

My essay is posted here. I invite feedback to improve the article, as well as general discussion of the idea.

—John

In reply to Lazy Lists as a model for implicit parallelism by John M. Dlugosz

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