number to binary

number-to-binary.rkt

#lang racket
(define (get-spaces-inner n spaces)
  (define current-space (car spaces))
  (if (> current-space n)
      (cdr spaces)
      (get-spaces-inner n (cons (* current-space 2) spaces))))

(define (get-spaces n)
  (get-spaces-inner n '(1)))

(define (to-binary x spaces)
  (define binary-digits
    (first
     (foldl (lambda (place val)
              (define digits (first val))
              (define n (second val))
              (if (>= n place)
                  (list (cons 1 digits) (- n place))
                  (list (cons 0 digits) n)))
            (list '() x)
            spaces)))
    (reverse binary-digits))

(define (number-to-binary n)
  (define spaces (get-spaces n))
  (to-binary n spaces))