Martin Pomije wrote:

> This is my solution to Ex. 6 on p. 97 of Paul Graham's "ANSI Common
> Lisp"
>
> <QUOTE>
> 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)
> <\QUOTE>
>
> (I'll just ask about the iterative solution I developed.)
>
> ;;;;Ex. 6
> (defun intersperse (element list)
> (let ((return-list (list (car list))))
> (do ((rest-input-list (cdr list) (cdr rest-input-list))
> (rest-return-list return-list (cddr rest-return-list)))
> ((not (consp rest-input-list)) return-list)
> (setf (cdr rest-return-list)
> (list element (car rest-input-list))))))

newLISP

(define (intersperse sep seq , A B)
(if (unify '(A B) (slice seq 0 2))
(begin (bind $it)
(append (list A sep) (intersperse sep (rest seq))))
seq))

(intersperse '- '(a b c d e f))

(a - b - c - d - e - f)