Higher-order functions in Elisp

Question

I created a function that returns a function in Elisp:

(defun singleton-set (elem)
  (defun f (n) (= n elem))
  f)

I try to run this in IELM, a

Answer 1

How to make functions returning functions possible in Emacs Lisp?

Using fake closures, and lexical-let.

What is the reason this mechanism is different from other languages like Python, Scala or Clojure?

Richard Stallman answered this question in a paper he wrote a while ago.