retrying something 3 times before throwing an exception - in clojure

Question

I don\'t know how to implement this piece of Python code in Clojure

for i in range(3):
    try:
        ......
    except e:
        if i == 2:
            raise         


        

Answer 1

You can do like this:

(defn retry
  "Tries at most n times, return first try satisfying pred or nil"
  [times pred? lazy-seq]
  (let [successful-trial (drop-while (complement pred?) (take times lazy-seq))]
    (if (empty? successful-trial)
        nil
        (first successful-trial))))

Then you could use the function as such:

(when-not (retry 3 pos? (repeatedly #(rand-nth [-1 -2 -3 2 1]))
    (throw (Exception. "my exception message"))

This would try at most three times to take a positive number at random from the vector and if it doesn't succeed, throws an exception.