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)

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