Thank you for your answer David.
I think I am confused about how to distinguish between a symbol and a
variable, as I thought that the symbol being derefed pointed to the atom
that it was made to define when transparent-chan was called.
Also, I am trying to specifically solve the logging problem to understand
how I might use stored values or state outside the scope of the channel as
a means of creating the illusion of referencing its contents. Later I was
thinking about incorporating it into a gui to see if it's possible to
design an asynchronous message passing system using drag and drop icons
that represent pubs and subs, channels with a drop-down contents tab, and
running listening processes. I know this is probably out of my league, but
I was just asking myself how something like that might be implemented. I
will of course continue to learn and reinforce the basics though on my own.
Jesse
On Monday, May 12, 2014 1:26:57 PM UTC+9, David Della Costa wrote:
>
> I apologize, apparently you can't use go-loop how I did below,
>
> => (def my-go-loop (async/go-loop [msg (async/<! c)] (println "got msg "
> msg " from channel " 'c)))
>
> ...try this instead:
>
> (def my-go-loop (async/go-loop [] (let [msg (async/<! c)] (println "got
> msg " msg " from channel " 'c))))
>
> Sorry about that!
>
> DD
>
> (2014/05/12 13:21), Dave Della Costa wrote:
> >
> >> 1) I feel like it is a redundant to define bindings multiple times in
> >> my go's let exprs when the params have already been passed in as
> >> arguments. Is there a more idiomatic way to do this?
> >
> > I think the fact that you are re-binding in a let should show you that
> > these variables are already in scope: that let is wholly redundant, just
> > remove it.
> >
> >
> >> 2) Whenever I try to create a generic process to automatically
> >> generate a log-name for each channel and then call update, I get a
> >> 'symbol cannot be cast to atom' error. How can I get around this? It
> >> seems to happen even if I don't use the log-name function.
> >
> > It's simple: a symbol is not an atom. It's telling you exactly what you
> > need to know: you cannot call swap! on a symbol. Make sure your atom is
> > the first argument to swap! wherever you use it.
> >
> >
> >> 3) Is there a better way to keep track of what's on a channel that
> >> doesn't use macros?
> >
> > You cannot look inside of a channel, but to do what you want and get a
> > sense of how core.async works, I think you are on the right track by
> > logging as you put stuff in and take it out.
> >
> > That said, I would start by getting rid of the log and the macro--these
> > are unnecessary complications--and do things very simply:
> >
> > => (require '[clojure.core.async :as async])
> > nil
> > => (def c (async/chan))
> > #'user/c
> > => (def my-go-loop (async/go-loop [msg (async/<! c)] (println "got msg "
> > msg " from channel " 'c)))
> > #'user/my-go-loop
> > => (defn put-and-print! [c msg] (println "putting msg " msg " onto
> > channel " 'c) (async/put! c msg))
> > #'user/put-and-print!
> > => (put-and-print! c "I am a message!")
> > putting msg I am a message! onto channel c
> > got msg I am a message! from channel c
> > nil
> > =>
> >
> > Printing out "channel c" is kind of silly since there is only one, but
> > it sounds like you may want to do this with multiple channels so this is
> > one way to print out the variable name--simply quote it.
> >
> > DD
> >
> > (2014/05/12 11:41), gamma235 wrote:
> >> Hi everyone,
> >>
> >> I am getting my feet wet with core.async and am trying to attach atoms
> >> to channels that update automatically and print out to the console as
> >> you take and put. This is not for anything serious, just a way to get
> >> familiar with the behavior and functionality of the library and
> practice
> >> my Clojure skills. Thanks in advaan
> >>
> >> Here is my code:
> >>
> >> (defn log-name [ch] (symbol (str ch '-log)))
> >>
> >> ;; Is this efficiently written?
> >> (defmacro transparent-chan [ch]
> >> (do
> >> `(def ~ch (chan))
> >> `(def (log-name ~ch) (atom []))
> >> `(println "new transparent channel created!")))
> >>
> >> (defn- update [log v]
> >> (do
> >> (swap! log conj v)
> >> (println "log test passed: " v " has been logged")
> >> (println "channel contents: " @log)))
> >>
> >> (defn transparent-put [ch v]
> >> (let [log (log-name ch)]
> >> (go
> >> (let [ch ch
> >> v v]
> >> (>! ch v)
> >> (println v " has been successfully moved through the
> channel")))
> >> (update log v)
> >> (println "put test passed: " v " has been put on the channel")
> >> (println " rechecking channel contents: " @log)))
> >>
> >> (defn transparent-take [ch]
> >> (go
> >> (let [v (<! ch)
> >> log-name (symbol (str ch '-log))]
> >> (swap! log-name #(remove #{v} %))
> >> (println v "has been removed from channel")))
> >> (println " removal pending"))
> >>
> >>
> >>
> >> ;; tests
> >> (transparent-chan c)
> >> c
> >> c-log
> >> @c-log
> >> (transparent-put c 42)
> >> (transparent-take c)
> >>
> >>
> >>
> >> My main questions are regarding variable scope:
> >> 1) I feel like it is a redundant to define bindings multiple times in
> my
> >> go's let exprs when the params have already been passed in as
> arguments.
> >> Is there a more idiomatic way to do this?
> >>
> >> 2) Whenever I try to create a generic process to automatically generate
> >> a log-name for each channel and then call update, I get a 'symbol
> cannot
> >> be cast to atom' error. How can I get around this? It seems to happen
> >> even if I don't use the log-name function.
> >>
> >> 3) Is there a better way to keep track of what's on a channel that
> >> doesn't use macros?
> >>
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