binary-trees Racket CS program

#lang racket/base

;;; The Computer Language Benchmarks Game
;;; https://salsa.debian.org/benchmarksgame-team/benchmarksgame/

;;; Derived from the Chicken variant by Sven Hartrumpf
;;; contributed by Matthew Flatt
;;; *reset*

(require racket/cmdline)

(struct node (left val right))

;; Instead of (define-struct leaf (val)):
(define (leaf val) (node #f val #f))
(define (leaf? l) (not (node-left l)))
(define (leaf-val l) (node-val l))

(define (make item d)
  (if (= d 0)
      (leaf item)
      (let ((item2 (* item 2))
            (d2 (- d 1)))
        (node (make (- item2 1) d2) 
              item 
              (make item2 d2)))))

(define (check t)
  (if (leaf? t)
      1
      (+ 1 (+ (check (node-left t)) 
                         (check (node-right t))))))

(define (main n)
  (let* ((min-depth 4)
         (max-depth (max (+ min-depth 2) n)))
    (let ((stretch-depth (+ max-depth 1)))
      (printf "stretch tree of depth ~a\t check: ~a\n"
              stretch-depth
              (check (make 0 stretch-depth))))
    (let ((long-lived-tree (make 0 max-depth)))
      (for ((d (in-range 4 (add1 max-depth) 2)))
        (let ((iterations (arithmetic-shift 1 (+ (- max-depth d) min-depth))))
          (printf "~a\t trees of depth ~a\t check: ~a\n"
                  iterations
                  d
                  (for/fold ([c 0])
                            ([i (in-range iterations)])
                    (+ c 
                       (check (make i d)) )))))
      (printf "long lived tree of depth ~a\t check: ~a\n"
              max-depth
              (check long-lived-tree)))))

(command-line #:args (n) 
              (main (string->number n)))
    

NOTES:
64-bit Ubuntu quad core
Welcome to Racket v7.7.0.4 [cs].


Thu, 07 May 2020 16:15:42 GMT

MAKE:
make: *** No rule to make target 'binarytrees.racketcs_run'.  Stop.

0.07s to complete and log all make actions

COMMAND LINE:
/opt/src/racket-7.7.0.4-cs/bin/racket binarytrees.racketcs 21

PROGRAM OUTPUT:
stretch tree of depth 22	 check: 8388607
2097152	 trees of depth 4	 check: 65011712
524288	 trees of depth 6	 check: 66584576
131072	 trees of depth 8	 check: 66977792
32768	 trees of depth 10	 check: 67076096
8192	 trees of depth 12	 check: 67100672
2048	 trees of depth 14	 check: 67106816
512	 trees of depth 16	 check: 67108352
128	 trees of depth 18	 check: 67108736
32	 trees of depth 20	 check: 67108832
long lived tree of depth 21	 check: 4194303