On 12/7/11 10:21 AM, Henrik Nilsson wrote:
I also had a look at John Millikin's page on Understanding Iteratees, which is very good:
https://john-millikin.com/articles/understanding-iteratees/
But, the intuition that comes across there is:
* iteratee: a stream (of sorts) consumer
* enumerator: a stream (of sorts) producer
* enumeratee: a stream (of sorts) transformer
And "iterator" isn't mentioned at all.
The "iterator" terminology is from the object-oriented world; iteratees are explicitly offered as an alternative to the iterator approach, which is why we don't have iterators. An iterator is something which iterates over a collection--- to produce the elements in that collection. In the iterator approach the sink (the for-loop) is in charge and it pulls the data from the source (the iterator). The problem, of course, is that the source never knows whether the sink will pull the next element or not, so it never knows when it's done. An iteratee is also something which iterates over a collection--- to consume the elements in that collection. In the iteratee approach the source (the enumerator) is in charge and it pushes the data into the sink (the iteratee) until the sink declares that it's had enough! and then the source knows it's done and it can free whatever resources need freeing. So there are actually two issues going on here: one is the source-vs-sink distinction, and the other is the active-vs-passive or push-vs-pull distinction. Since we have two binary features, we can have them be aligned in parallel or in opposition (which one is which is irrelevant). iterator-style --- source : sink :: passive : active iterator = passive source for-loop = active sink (pull) iteratee-style --- source : sink :: active : passive enumerator = active source (push) iteratee = passive sink The "enumeratee" terminology comes from a pun about something which is both an "enumerat(or)" and also an "(iterat)ee". However, it would have been much clearer IMO if instead we had used this terminology retroactively as a name for the for-loop or other active sink in the iterator style. If this had been done, then we could use the following analysis: iterat- = passive enumerat- = active -or = source -ee = sink Which preserves the analogy you want. "Employers" are the source of employment, and "employees" are the sinks/consumers of employment. To make sense of the active-vs-passive distinction, rather than thinking about the employers as the ones being active (i.e., thinking of employment as the commodity), we could instead choose to frame our discourse around "workers" as the source of work (i.e., thinking of labor as the commodity). In this case we would expect "workees" to be the consumers of work/labor; but, alas, we have no word for rendering employers as passive participants in the world of economic transactions. -- Live well, ~wren