Create fibmorse sequence in racket

fibmorse.rkt

#lang racket

(define (next-value current-value)
  (if (= current-value 0)
      (if (= (random 2) 0) '(1) '(1 0))
      '(0 1)))

(define (do-sub myl)
  (apply append
         (map next-value myl)))

(define (gen-seq desired-len)
  ; local function iter
  (define (iter init-lst desired-len)
    (if (>= (length init-lst) desired-len)
        (take init-lst desired-len)
        (iter (do-sub init-lst) desired-len)))
  ; body of gen-seq calls iter
  (iter (list (random 2)) desired-len))

(define (filter-len myl by-val)
  (length (filter (lambda (val) (= val by-val)) myl)))

(define (balance myl)
  (- (filter-len myl 1)
     (filter-len myl 0)))

; test
(define my-seq (gen-seq 20))

(println my-seq)
(balance my-seq)