I tried it in ClojureScript and I did get the same error as your did. I believe
this is because the go-macro doesn't handle the case-statement correctly (or,
rather, not at all). Switching from (case key ...) to (condp = key ...) however
appears to do the trick (along with all the other awkward namespacing stuff):
(defmacro dispatch-on [ch & cases]
(let [argssym (gensym "args__")
keysym (gensym "key__")
ressym (gensym "res__")
default-case (when (odd? (count cases)) (last cases))
default-case (when default-case
(let [[[res] & body] default-case]
`(cljs.core/let [~res ~ressym] ~@body)))
cases (if default-case (butlast cases) cases)
case-body (apply concat (for [[key [args & body]] (partition 2 cases)]
[key `(cljs.core/let [~args ~argssym]
~@body)]))
case-body (if default-case
(conj (vec case-body) default-case)
case-body)]
`(cljs.core/let [ch# ~ch
~ressym (cljs.core.async/<! ch#)]
(if (cljs.core/and (cljs.core/vector? ~ressym) (cljs.core/seq ~ressym))
;; <- still problematic
(cljs.core/let [~keysym (cljs.core/first ~ressym)
~argssym (cljs.core/next ~ressym)]
(cljs.core/condp = ~keysym ~@case-body))
~default-case))))
However, this still gives an error if you put :foobar onto the channel. This,
too, appears to be a core.async bug: in the line highlighted above, *both*
arguments to "and" get evaluated, regardless of whether the first argument is
false or not.
Am Dienstag, 22. Juli 2014 20:46:45 UTC+2 schrieb Tom Locke:
> On Tuesday, 22 July 2014 16:42:00 UTC+2, Kevin Marolt wrote:
> > Not sure if I understood the initial question correctly, but isn't the
> > following sort of what you wanted?
>
> Yes that's exactly what I was after, although that is Clojure, right? I've
> tried it in ClojureScript (not much to change - just requiring the right
> namespaces / macros) and it doesn't work. I get:
>
> No implementation of method: :emit-instruction of protocol:
> #'cljs.core.async.impl.ioc-macros/IEmittableInstruction found for class:
> cljs.core.async.impl.ioc_macros.Jmp
>
> I've tried playing around moving the <! and the (recur) outside of the
> on-dispatch macro, and, while I can avoid the above error and get it to
> compile, the behaviour of the test code makes no sense at all. It seems like
> mixing the go macro with your own macros is very fragile in cljs.
>
> Tom
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