Michael Dowling has a new post to his site announcing a project he's recent released to try to bring some of the functionality of Clojure to PHP with the introduction of transducers.
He starts with an official definition of what a transducer is from the Clojure documentation then explains it in a bit more layman's terms as "a fancy way of saying that you can use functions like map and filter on basically any type of data source (not just sequences)" and can output any kind of structure as a result. He then gets into some code examples using his project showing eager and lazy evaluation, how they're composable and a list of the ones the library makes available (and what they do). He then gets into a more complete example of their application with a streams example, working with/modifying a string. He ends the post looking at how to create your own custom transducer and how they compare to generators.