Scheme function to duplicate every element of a list a specified number of times

Question

This code takes a list and a integer and duplicates every element in the list the specified number of times.

(define (super-duper source count)
        (define (next-super source left)
                (if (zero? left)
                        (super-duper (cdr source) count)
                        (cons (super-duper (car source) count) (next-super source (- left 1)))))

        (if (pair? source)
                (cons (super-duper (car source) count) (next-super source (- count 1)))
                source))

(display(super-duper '((x y) t) 3))

Answer 1

I think you need to decide weather to repeat only on the first level of the list, or if you want to do a tree walk for lists inside lists. As is, this code produces a weird combination of both in an exponential explosion of the list, The following sample returns over 2 million leaf elements for an input of length 26 and a repeat of 10.

(leaf-count (super-duper '(a (b (c (d (e f g (h i) j k) l m n o) p q ) r (s t (u v) w ) x y) z) 10)) 
->> 2576420

(define (leaf-count Tree)
  (cond ((null? Tree) 0)
        ((not (pair? Tree)) 1)
        (else (+ (leaf-count (car Tree))
                 (leaf-count (cdr Tree))))))