Mastering Functional Programming

Visited links

The caveat that has the most impact here is the partiality of tracking of the actors that this actor has already visited. If you remember, in the sequential example, we are using the foldLeft function to accumulate the results of every URL processing, and at all times we have a complete, up-to-date list of all the URLs collected by the entire application. This means the recursive crawling calls always have a full picture of what the application has collected so far.

In the diagram, we see a sequential example of processing with foldLeft:

All the nodes that were already processed are highlighted in green, and the current URL is ...