scheme, gauche, decimal, binary

dec2bin.scm

(define (quotient-down n divider)
  (let loop ((n n)(acc '()))
    (if (zero? n)
        acc
        (loop (quotient n divider)(cons n acc)))))

(define (number-list->number lis)
  (string->number (string-join (map x->string lis) "")))

(define (dec->bin n)
  (number-list->number
   (map (lambda (e)
          (if (zero? (remainder e 2)) 0 1))
        (quotient-down n 2))))


(dec->bin 172)
(number->string 172 2)

(dec->bin 60)
(number->string 60 2)

(dec->bin 128)
(number->string 128 2)

(dec->bin 100)
(number->string 100 2)



(define (number->number-list n)
  (map (compose string->number string)
       (string->list (number->string n))))

(use srfi-1)
(define (reverse-index-expt ls)
  (unfold null?
          (lambda (s)
            (expt 2 (- (length s) 1)))
          cdr ls))

(define (bin->dec n)
  (let1 bls (number->number-list n)
    (apply + (filter-map (lambda (b e)
                           (and (= b 1) e))
                         bls
                         (reverse-index-expt bls)))))

(bin->dec 10011001)
(bin->dec 1111)
(bin->dec 1101)
(bin->dec 1110)