clojure.lang.Atom cannot be cast to a java.lang.Num

[Dylan Gleason]

I am trying to read a TCP request via an instance of DataInputStream and am running into this error with the following code:

(defn receive

  [socket]

  (with-open [reader (DataInputStream. (.getInputStream socket))]

    (let [length   (read-length reader)

          bytes-in (byte-array length)

          offset   (atom 0)

          index    (atom 0)]

      (while (not= -1 @offset)

        (reset! offset (.read reader bytes-in offset (- length index)))

        (reset! index (+ index offset))))))

For some reason, trying to update the value in offset appears to result in this casting error. I tried testing a similar expression at the REPL, and it works, e.g.

> (def blah (atom 0))

> (reset! blah 93)    ; no error

It seems odd that Clojure would complain about this, since "93" is an instance of java.lang.Long -- why would Clojure be so annoyingly anal-retentive when setting the atom to a java.lang.Num? Also, if anyone has any ideas on how to make achieve this without using atoms, and what the best approach would be (a recursive solution using loop-recur, perhaps?)

[Ambrose Bonnaire-Sergeant]

You're adding two atoms together here:  (reset! index (+ index offset))

Thanks,

Ambrose

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[Philippe Guillebert]

Also, you should be using loop/recur instead of mutating atoms here, this is the functional way.

You already laid out your 2 loop bindings, and a stop condition. This should be straightforward.

Philippe.

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[Dylan Gleason]

Thank you, Ambrose. It appears I forgot to dereference both index and offset when trying to read the values associated with the atoms. Thanks Phillippe -- I went with your recursive solution and bypassed mutation via atoms altogether -- a much cleaner solution.

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