tspl.scm

(define even?
  (lambda (x)
    (cond ((= x 0) #t)
    (else (odd? (- x 1))))))

(define odd?
  (lambda (x)
    (cond ((= x 0) #f)
    (else (even? (- x 1))))))

(define list-ref
  (lambda (ls pos)
    (cond ((= pos 0) (car ls))
    (else (list-ref (cdr ls) (- pos 1))))))

(define list-tail
  (lambda (ls pos)
    (cond ((= pos 0) ls)
    (else (list-tail (cdr ls) (- pos 1))))))