Wolfhard Buss wrote:

> * Martin Pomije with an exercise from Paul Grahams ACL:
>
> > Define iterative and recursive versions of a function that takes an
> > object and a list, and returns a new list in which the object appears
> > between each pair of elements in the original list:
> >
> > > (intersprerse '- '(a b c d))
> > (A - B - C - C)
>
>
> The iterative variant (loop-less):
>
> (defun intersperse (object list)
> (let ((result (and list (list (first list)))))
> (dolist (item (rest list) (nreverse result))
> (setq result (list* item object result)))))
Gauche Scheme

(use srfi-1) ;; circular-list

(define (intersperse x xs)
(cdr (append-map list
(circular-list x)
xs)))

(intersperse '- '(b c d j))
===>
(b - c - d - j)