You changed the structure, though, to use something much closer to a cond instead of an if. Also, there are variants that require fewer ()s for this.

clisp:

    (defun factorial (n) (cond
        ((<= n 1) 1)
        (T        (* n (factorial (- n 1))))))

Clojure (which I believe is similar to Ark with respect to not using extra parentheses around cond clauses, but I don't have Ark setup to verify that that's actually the case and then to test my demonstration with, so I'm going to do it with Clojure, despite the "weird" [] syntax, as it is orthogonal to the demonstration):

    (defn factorial [n] (cond
        (<= n 1) 1
        :else    (* n (factorial (dec n)))))

fair point (i was actually planning on adding a lisp cond by way of contrast, and then forgot). my contention is that the ml cond looks a lot less cluttered than the lisp one, and is therefore more pleasant to read.

the clojure one is nicer since it lacks the visual clutter of the per-case enclosing parens, but it feels slightly wrong from a lisp perspective since i'm now replacing [(a, b), (c, d)] with [a, b, c, d] which has changed the innate structure of the expression.

i actually like the racket convention of using square brackets to distinguish this the best of all the lispy options:

    (defn factorial [n]
      (cond
        [(<= n 1) 1]
        [:else    (* n (factorial (dec n)))]))

For the record, that isn't valid racket code. This is:

  (define (factorial n)
    (cond
     [(<= n 1)  1]
     [else      (* n (factorial (sub1 n)))]))