#lang racket

(define (list-length list)
  (match list
    [`() 0]
    [(cons head tail) (cons (f head)
                            (list-length f tail))]))

(module+ test
    (require rackunit)
    (check-equal? (list-length '(1 2 3)) 3)
    (check-equal? (list-length '()) 0))

(define (my-map2 f lst)
  (match lst
    ['() '()]
    [(list head tail ...) (cons (f head)
                                (my-map2 f tail))]))