Idiomatic clojure for progress reporting?

Question

How should I monitor the progress of a mapped function in clojure?

When processing records in an imperative language I often print a message every so often to indica

Answer 1

I don't know of any existing ways of doing that, maybe it would be a good idea to browse clojure.contrib documentation to look if there's already something. In the meantime, I've looked at your example and cleared it up a little bit.

(defn report [cnt]
  (when (even? cnt)
    (println "Done" cnt)))

(defn report-progress []
  (let [aseq (range 10)]
    (doall (map report (take (count aseq) (iterate inc 1))))
    aseq))

You're heading in the right direction, even though this example is too simple. This gave me an idea about a more generalized version of your report-progress function. This function would take a map-like function, the function to be mapped, a report function and a set of collections (or a seed value and a collection for testing reduce).

(defn report-progress [m f r & colls]
  (let [result (apply m
                 (fn [& args]
                   (let [v (apply f args)]
                     (apply r v args) v))
                 colls)]
    (if (seq? result)
      (doall result)
      result)))

The seq? part is there only for use with reduce which doesn't necessarily returns a sequence. With this function, we can rewrite your example like this:

user> 
(report-progress
  map
  (fn [_ v] v)
  (fn [result cnt _]
    (when (even? cnt)
      (println "Done" cnt)))
  (iterate inc 1)
  (range 10))

Done 2
Done 4
Done 6
Done 8
Done 10
(0 1 2 3 4 5 6 7 8 9)

Test the filter function:

user> 
(report-progress
  filter
  odd?
  (fn [result cnt]
    (when (even? cnt)
      (println "Done" cnt)))
  (range 10))

Done 0
Done 2
Done 4
Done 6
Done 8
(1 3 5 7 9)

And even the reduce function:

user> 
(report-progress
  reduce
  +
  (fn [result s v]
    (when (even? s)
      (println "Done" s)))
  2
  (repeat 10 1))

Done 2
Done 4
Done 6
Done 8
Done 10
12