Thanks much. Your approach is much better than mine. I was looking for a
good excuse to use a macro, but I suppose I will postpone that for another
day.
On Tuesday, December 10, 2013 2:03:07 PM UTC-5, James Reeves wrote:
>
> On 10 December 2013 18:24, larry google groups
> <lawrenc...@gmail.com<javascript:>
> > wrote:
>
>>
>> > As an aside, this doesn't look like a good use-case for macros
>> >. You'd probably be better defining a map with keys for :
>> > worker, :channel, etc. Either that or a protocol.
>>
>> Thank you much for your help. But I thought this is exactly what macros
>> were for? In another language I would end up just copying-and-pasting the 4
>> defs, and then changing "update" to "remove" so I could have both an update
>> channel and a remove channel. I thought that macros were suppose to be good
>> at removing that kind of redundancy?
>>
>
> Macros should be considered a "last resort" feature. They are usually the
> worst way of solving a problem, unless they are the *only* way of solving
> a problem.
>
> Let's consider the functions your macros produce (ignoring the channel for
> now):
>
>
> (add-to-update-channel document)
>
> (update-mongo-worker)
>
> (start-mongo-channel)
>
>
> These functions are very specific, but we can make them more
> general-purpose by adding an additional argument:
>
> (add-to-channel mongo-updates document)
>
> (update-worker mongo-updates)
>
> (start-channel mongo-updates)
>
>
> Since these are generic functions, any specific functionality must be
> defined by the new "mongo-updates" argument. In your example there are two
> things specific to the mongo update job: the channel, and the function to
> execute.
>
> We could place these two piece of information in a data structure:
>
> (def mongo-updates
>
> {:channel (channel)
>
> :to-execute println})
>
>
> Or we could define a type or protocol. For now the map seems good enough,
> and we can use it to build generic versions of the functions generated by
> your macro:
>
> (defn add-to-channel [{:keys [channel]} data]
> (enqueue channel document))
>
> (defn update-worker [{:keys [channel to-execute]}]
> (loop [document @(read-channel channel)]
> (to-execute document)
> (recur @(read-channel channel))))
>
> (defn start-channel [worker-info]
>
> (dotimes [_ 6]
>
> (future (update-worker worker-info))))
>
>
> - James
>
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