I ran into the other half of this problem: If you expect nils to signify
closed channels, then you can't leverage the logically false nature of nil
without excluding explicit boolean false values. Given the pleasant syntax
of if-let / <! pairs, I reworked my early experiments to use if-recv which
is defined as follows:
(defmacro if-recv
"Reads from port, binding to name. Evaluates the then block if the
read was successful. Evaluates the else block if the port was closed."
([[name port :as binding] then]
`(if-recv ~binding ~then nil))
([[name port] then else]
`(let [~name (<! ~port)]
(if (nil? ~name)
~else
~then))))
I've considered some alternative core.async designs, such as an additional
"done" sentinel value, or a pair of quote/unquote operators (see
"reduced"), but nothing seems as simple as just avoiding booleans and nils,
as annoying as that is. I'd be curious to here what Rich & team considered
and how they're thinking about it. However, my expectation is that the nil
approach won't change, since it's pretty much good enough.
On Thursday, August 15, 2013 10:44:48 PM UTC-4, Mikera wrote:
>
> Hi all,
>
> I'm experimenting with core.async. Most of it is exceptionally good, but
> bit I'm finding it *very* inconvenient that nil can't be sent over
> channels. In particular, you can't pipe arbitrary Clojure sequences through
> channels (since sequences can contain nils).
>
> I see this as a pretty big design flaw given the ubiquity of sequences in
> Clojure code - it appears to imply that you can't easily compose channels
> with generic sequence-handling code without some pretty ugly special-case
> handling.
>
> Am I missing something? Is this a real problem for others too?
>
> If it is a design flaw, can it be fixed before the API gets locked down?
>
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