Scheme and Clojure don't have the atom type predicate - is this by design?

Question

Common LISP and Emacs LISP have the atom type predicate. Scheme and Clojure don't have it. http://hyperpolyglot.wikidot.com/lisp

Is there a design reason for this - or is it just not an essential function to include in the API?

Answer 1

Clojure has the coll? (collection?) function, which is (sort of) the inverse of atom?.

Answer 2

In the book The Little Schemer, atom? is defined as follows:

(define (atom? x)
  (and (not (pair? x))
       (not (null? x))))

Noting that null is not considered an atom, as other answers have suggested. In the mentioned book atom? is used heavily, in particular when writing procedures that deal with lists of lists.