Yes, that makes sense that you can't make that assumption. You'd have to
create something like what I was discussing above:
(defn map-indexed-transducer-base [f box-mutable inc-mutable]
(fn [rf]
(let [i (box-mutable -1)]
(fn
([] (rf))
([result] (rf result))
([result input]
(rf result (f (inc-mutable i) input)))))))
;; this is the version that Léo would want
(defn map-indexed-transducer-single-threaded [f]
(map-indexed-transducer-base f unsynchronized-mutable-long!
#(unsynchronized-mutable-swap!
% inc))
;; this is the version included in clojure.core
(defn map-indexed-transducer-sequentially-accessed-by-different-threads [f]
(map-indexed-transducer-base f volatile! #(vswap! % inc))
;; this works with `fold` and gives you all the indices at least, but in a
nondeterministic order
(defn map-indexed-transducer-concurrently-accessed-by-different-threads [f]
(map-indexed-transducer-base f atom #(swap! % inc)) ; or an AtomicLong
variant
On Monday, April 10, 2017 at 1:06:14 PM UTC-4, Alex Miller wrote:
>
>
> On Monday, April 10, 2017 at 11:48:41 AM UTC-5, Alexander Gunnarson wrote:
>>
>> Léo, I definitely agree that you can use unsynchronized mutable stateful
>> transducers *as long as you can guarantee they'll be used only in
>> single-threaded contexts. *
>>
>
> Transducers included in core cannot make the assumption that they will
> only be used that way. (But you may be able to guarantee that with your
> own.)
>
>
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