Okay; thanks for the answer! I understand now.
On Apr 29, 11:52 pm, Konrad Hinsen <konrad.hin...@laposte.net> wrote:
> On 29.04.2009, at 21:44, samppi wrote:
>
> > Could someone give me a simple example of when
> > clojure.contrib.accumulators is useful? Its use seems to involve
> > collections (and numbers) that have the :clojure.contrib.accumulators/
> > accumulator type, and it has some general multimethods for adding and
> > combining, but what does it add that conj and concat do not provide?
> > contrib.monads/writer-m seems to suggest using accumulators, too...
>
> My main motivation for writing that library was to have a generic
> interface to many kinds of accumulators for use in contrib.monads/
> writer-m. The writer monad is of little use if a specific type of
> accumulator is hard-coded into it, as different applications need to
> accumulate quite different data items. The same need for a generic
> interface exists in other situations. For example, in one of my
> applications I have a tree data structure with a generic "accumulate
> leaf values" operation that uses the accumulator multimethods.
>
> In addition to the generic accumulator interface, the accumulator
> library contains implementations of non-trivial accumulators such as
> counter, min-max, or mean-variance. I use these three a lot for
> statistics, with counter for producing histograms.
>
> Konrad.
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