How to create and add elements to the list in the Scheme?

Question

I want to define a method that takes an integer as input and dynamically creates a list of all descending integers to zero. I find a problem with calling a method for element n-1

Answer 1

It is not all so beautiful, but it should work, tested in DrScheme.

(define (gen-list x )
  (if (= x 0) (list 0) (cons x (gen-list (- x 1)))))

Answer 2

Now, when it comes to homework, I think the alternative could be a recursive version of the tail.

  (define (gen-list x)  
           (let lp ((n 0) (ret '())) 
              (if (> n x) 
              ret 
              (lp (1+ n) (cons n ret)))))

Answer 3

If you use the PLT scheme, the concept library will allow you to do this quite accurately:

; natural -> (listof natural)
(define (list-to-zero start-num)
 (for/list ([i (in-range start-num 0 -1)])
  i))

Just an alternative to a recursive form ...