Idiomatic lisp - loops

Hi,

I'm trying to write a loop that inserts a dotted key/value pair in
order into a list of ordered
key/value pairs.

So far I've got a recursive solution:

(defun kv-insert (list elt)
(if (null list) '()
(let* ((h (car list))
(k1 (car elt))
(k2 (car h)))
(cond ((string< k1 k2) (cons elt list))
((string= k1 k2) (cons elt (cdr list)))
(t (cons h (kv-insert (cdr list) elt)))))))

and an iterative solution:

(defun kv-insert (list elt)
(let ((k1 (car elt))
(acc '()))
(while (not (null list))
(let* ((h (car list))
(k2 (car h)))
(cond ((string< k1 k2)
(setq acc (append (reverse list)
(list elt)
acc))
(setq list '()))
((string= k1 k2)
(setq acc (append (reverse (cdr list))
(list elt)
acc))
(setq list '()))
(t (setq acc (cons h acc)))))
(setq list (cdr list)))
(reverse acc)))

neither of which I'm particularly happy with.

In scheme I would use letrec to avoid needing to pass the elt
parameter to each
loop iteration. Is there something similar in lisp or an alternative
idiomatic way
to write this loop?

(define (kv-insert l elt)
(letrec ((k1 (car elt))
(loop (lambda (l)
(if (null? l) '()
(let* ((h (car l))
(k2 (car h)))
(cond ((string< k1 k2) (cons elt l))
((string= k1 k2) (cons elt (cdr l)))
(else (cons h (loop (cdr l))))))))))
(loop l)))

Thanks,

Ian

.

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