Detecting the caller of a function in Scheme or Racket
(define atom? (lambda (x) (and (not (pair? x)) (not (empty? x)))))

(define lat? (lambda (l)
               (define latt?
                 (lambda (l)
                   (cond
                     ((null? l) #t)
                     ((atom? (car l)) (latt? (cdr l)))
                     (else #f))))
               (if (null? l) #f (latt? l))))

(define lat?
  (lambda (l)
    (cond
      ((and (null? l) (called-by "lat?")) #t)
      ((atom? (car l)) (lat? (cdr l)))
      (else #f))))