collatz in racket

c.rkt

#lang racket


(define (foo n)
  (if (= (modulo n 2) 0)
      (/ n 2)
      (+ (* 3 n) 1)
  ))

(define (goo a)
  (println a)
  (if (= (first a) 4)
      a
      (goo (cons (foo (first a)) a))
      )
  )

(goo (list 100))