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
[email protected]
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