Michael, That's a fair summary of the operation of `run`.
The outer send does not affect the agent's state because — as you said — its primary responsibility is to coordinate the dispatch of each agent through the various stages in the FSM. You could certainly implement the specific FSM shown using a single function, but then (a) you could not cleanly distinguish between blocking and nonblocking operations and (b) you could not independently extend the FSM without modifying that uber-function. I hope this clarifies things? - Chas -- http://cemerick.com [Clojure Programming from O'Reilly](http://www.clojurebook.com) On May 19, 2012, at 3:46 AM, Michael Erickson wrote: > Hello all, > > I've been reading Clojure Programming by Emerick, Carper, and Grand from > O'Reilly and have a question. Towards the end of Chapter 4, they implement a > little web-crawler that uses agents. I'm having some trouble getting my head > around one piece of the code. Specifically the `run` function they define, > which I've pasted here: http://pastebin.com/EWqPaBPt. > > In human terms, I understand this code to: > > 1) `send` a function "foo" to the agent to execute it (this will happen in > another thread) > 2) "foo" figures out the function "bar" to call to transition to the next > state and calls it using either `send` or `send-off` as appropriate > 3) whatever "bar" happens to be, it is going to end with a call to run which > will keep the wheels of the state machine turning > > So my question is regarding the return form of the outer send, which is > `state`. Is the idea here to basically return the identity of the agent for > this outer send? Meaning, don't change anything this time, affect all change > via the inner send|send-off? > > I know I can't really make this assumption, but to simplify for a moment, > assume that these computations took place in three separate threads; A, B, > and C. > > A: call `run` > call send with "foo" (this will be executed in thread B) > return immediately since agents are asynchronous > > B: call "foo" with the agent > "foo" calls send|send-off with "bar" (this will be executed in thread C) > "foo" returns the agent as it was when it was called, so it's only real > purpose was to get "bar" going. > > C: call "bar" with the agent > this is where we actually do work and change the state of the agent > call `run` > > Am I on the right track? > > Best regards, > --mike > > Michael Erickson > erickson.mich...@gmail.com > > > -- > You received this message because you are subscribed to the Google > Groups "Clojure" group. > To post to this group, send email to clojure@googlegroups.com > Note that posts from new members are moderated - please be patient with your > first post. > To unsubscribe from this group, send email to > clojure+unsubscr...@googlegroups.com > For more options, visit this group at > http://groups.google.com/group/clojure?hl=en -- You received this message because you are subscribed to the Google Groups "Clojure" group. To post to this group, send email to clojure@googlegroups.com Note that posts from new members are moderated - please be patient with your first post. To unsubscribe from this group, send email to clojure+unsubscr...@googlegroups.com For more options, visit this group at http://groups.google.com/group/clojure?hl=en
