Question

As I understand it, recursing in Clojure without using the loop .. recur syntax might not be a problem for short sequences. However, using the loop .. recur syntax is the preferred method for writing recursive functions. So, I would like to start with the preferred method.

However, I have been struggling to convert this function [edit] which returns the skeleton of a sequence (the sequence structure without its values)

(defn skl
  [tree]
  (map skl (filter seq? tree)))

tested with this data

(def test_data1 '(1 (2 3) ( ) (( )) :a))
(def test_data2 '(1 2 (3 4) (5 ( 6 7 8))))

to loop .. recur syntax. Any ideas or pointers to examples would be appreciated.

Answer 1

You may want to look into the zipper library which allows for good structured tree editing, though it will likely be less elegant than your origional. I almost never need to use loop … recur. There is almost always a higher order function that solved the problem more elegantly with the same or better efficiency.

Replacing map with loop ... recur makes code more verbose and less clear. You also lose the benefits of chunked sequences.