Hi, I did some progress here, I was able to manage to create a custom
filter transducer that works seamlessly with regular values and channels
and can be composed with other transducers:
; on JVM I did this using protocols, but in ClojureScript I could not make
it work (some error when I tried to extend the ReadPort type), but this
works as same
(defn -expand [v f]
(if (satisfies? cljs.core.async.impl.protocols/ReadPort v)
(take! v f)
(f v)))
; my filter transducer that supports async operations
(defn filter-ext [pred]
(fn [f1]
(fn
([] (f1))
([result] (f1 result))
([result input]
(-expand (pred input); here is the trick, so in this case I made
every operation dependent on a callback, so they can be normalized
(fn [v]
(if v
(f1 result input)
result)))))))
(let [value-chan (fn [v] (let [c (chan 1)] ; simple helper to simulate an
async operation that just returns the input
(put! c v)
(close! c)
c))
xform (comp (filter-ext value-chan) ; ok, filter async
(filter-ext #(>= % 2))) ; now filter sync
c (chan 1 xform)]
(async/onto-chan c [1 false 2 3])
(go
(println (<! (async/into [] c))))) ; prints: [2 3]
I could have my extended versions of every transducer to add the support,
the code is pretty much the same but has the extra step of checking for the
returned value on the operation.
Not sure how that could ever be integrated into regular transducers (maybe
they could be extended somehow to include this feature selectively to avoid
the overhead), but for now this is the best that I could came up with.
---
Wilker Lúcio
http://about.me/wilkerlucio/bio
Woboinc Consultant
+55 81 82556600
On Sun, Sep 21, 2014 at 10:39 PM, Wilker <wilkerlu...@gmail.com> wrote:
>
> On Sun, Sep 21, 2014 at 10:08 PM, Sean Corfield <s...@corfield.org> wrote:
>
>>
> Hi Sean,
>
> Sorry, I don't really understood your suggestion... But let me try to make
> myself more clear of what I'm trying to accomplish:
>
> First let me say that I have a more Javascript background than Java, and
> my issue is more into ClojureScript world
>
> Javascript has a lot of async issues, specially when you are working on
> Node.JS world, every IO operation is async, although they have sync
> versions those versions block the world so I need to keep away from then,
> so, async callbacks is my only real options here.
>
> The first thing that I like to do in my async code is to wrap than into
> something that I can handle generically, in JS I used to do a lot of
> promises code, but now I'm core async, so I think making then "single
> channel value" just fits nice, and wrapping that way I can compose very
> well.
>
> Now I'm at this place, I have all those async functions that I wanna use
> to process my data, I wanna use those async functions, also regular
> functions.
>
> Before transducers, I've used the David Nolen's reactive helpers (on his
> blog source) to do my data processing using those channels, a good example
> on how I used to manage complex async pipelines are like this:
>
> (->> (scan-path "root/path") ; this will produce a channel that will
> output every file/dir path recursive from given path
> (r/filter-async is-file?) ; this requires async call to filter
> (f/filter (match-extension? #{"avi" "mpg"})) ; this will just check
> on the name, no async required
> (r/map-async read-hash-info) ; another async call, will generate a
> hash info from the path
> (r/map #(hash-map :hash %)) ; build a map from the value
> )
>
> So, I like how the previous code is build, because I can really just
> composed from my simple sync and async functions, but all these use "custom
> transducers" you can say...
>
> Then comes Transducers that can rise the bar on the abstraction level, so
> I now can get rid of all those custom transducers, right?
>
> So, it just would be nice if I could get the same clean way to build my
> pipeline like I did before, but with transducers.
>
> ---
> Wilker Lúcio
> http://about.me/wilkerlucio/bio
> Woboinc Consultant
> +55 81 82556600
>
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