#lang racket

(define atom? (λ (a) (and (not (pair? a)) (not (null? a)))))

;; The Little Schemer
;; 2. Do It, Do It Again, and Again, and Again...

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

(define (member? a lat)
  (cond
    ((null? lat) #f)
    (else (cond
            ((eq? a (car lat)) #t)
            (else
             (member? a (cdr lat)))))))

;; --- Tests -----------------------------------------------

(define (test-lat)
  (and
   (not (lat? '(1 2 3 ())))
   (lat? '(1 2 3))
   ))

(define (test-member)
  (and
   (member? 1 '(1 2 3))
   (member? 3 '(1 2 3))
   (not (member? 0 '(1 2 3)))
   ))

(define (test-all)
  (and
   (test-lat)
   (test-member)
   ))

(println (if (test-all) "OK" "Error"))