>
> I find this behaviour quite unfortunate because I now have to explicitly
> test
> for nil? and ensure consistent behaviour.
Yes, especially unfortunate considering that Rich said the reducers lib
could be used as a drop in replacement for core to speed up programs, or
something along the lines.
On Monday, October 29, 2012 2:00:35 PM UTC+1, Wolodja Wentland wrote:
>
> Hi all,
>
> I am currently testing performance of different reduce and map
> implementations
> in my programs and have problems because their treatment of nil is
> different.
> The "normal" clojure.core implementations of reduce and map work well when
> called on nil, but reduce-kv and functions in clojure.reducers throw
> exceptions.
>
> --- snip ---
> user=> (defn fold-into-vec
> "Provided a reducer, concatenate into a vector.
>
> Note: same as (into [] coll), but parallel."
> ([coll]
> (r/fold (r/monoid into vector) conj coll))
> ([n coll]
> (r/fold n (r/monoid into vector) conj coll)))
>
> user=> (map (fn [el] (* 2 el)) nil)
> ()
> user=> (mapv (fn [el] (* 2 el)) nil)
> []
> user=> (fold-into-vec (r/map (fn [el] (* 2 el)) nil))
> #<IllegalArgumentException java.lang.IllegalArgumentException: No
> implementation of method: :coll-fold of protocol:
> #'clojure.core.reducers/CollFold found for class: nil>
> user=> (reduce (fn [ret el] (+ el el)) {} nil)
> {}
> user=> (reduce (fn [ret [k v]] (+ k v)) {} nil)
> {}
> user=> (reduce-kv (fn [ret k v] (+ k v)) {} nil)
> #<IllegalArgumentException java.lang.IllegalArgumentException: No
> implementation of method: :kv-reduce of protocol:
> #'clojure.core.protocols/IKVReduce found for class: nil>
> --- snip ---
>
> I find this behaviour quite unfortunate because I now have to explicitly
> test
> for nil? and ensure consistent behaviour. This inconsistency violates the
> principle of least-surprise and I am not sure if the current behaviour is
> intentional or merely an unfortunate implementation detail.
>
> Wouldn't it make sense if reduce-kv and r/map mirror the behaviour of
> reduce,
> map and mapv in core?
>
> P.S. Would it be possible to have something like fold-into-vec in
> clojure.reducers?
> --
> Wolodja <[email protected] <javascript:>>
>
> 4096R/CAF14EFC
> 081C B7CD FF04 2BA9 94EA 36B2 8B7F 7D30 CAF1 4EFC
>
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