Question

(defn insert [s k]
    (let [spl (split-with #(< % k) s)]
       (concat (first spl) (list k) (last spl))))

(defn insert-sort [s]
    (reduce (fn [s k] (insert s k)) '() s))

(insert-sort (reverse (range 5000)))

throws a stack over flow error. What am I doing wrong here?

Answer 1

Same issue as with Recursive function causing a stack overflow. Concat builds up a bunch of nested lazy sequences like (concat (concat (concat …))) without doing any actual work, and then when you force the first element all the concats must get resolved at once, blowing the stack.