Re: Emacs Lisp's "mapconcat" in Common Lisp?

Pascal Bourguignon wrote:
 

Teemu Likonen <tlikonen@iki.fi> writes:
 

It's a Common Lisp newbie here; I'm more experienced in Emacs Lisp. I
wonder if there is similar function in CL like Emacs Lisp's "mapconcat":
 
    (mapconcat 'identity '("one" "two" "three") "-")
    => "one-two-three"
 
I can do the same in CL with this:
 
    (let ((list '("one" "two" "three")))
      (format nil "~{~a-~}~a" (butlast list) (car (last list))))
 
But I have a feeling that there could be a more elegant way. Is there?

 
Yes, write:       (mapconcat 'identity '("one" "two" "three") "-") ; elegant!
 
 
Of course, with:
 
 
(defun mapconcat (fun list sep)
   (when list
      (let ((~sep (with-output-to-string (*standard-output*)
                     (map nil (lambda (ch) (princ (if (char= #\~ ch) "~~" ch)))
sep))))
       (format nil (format nil "~~A~~{~A~~A~~}" ~sep)
               (funcall fun (first list))
               (mapcar fun (rest list))))))
 
 
 
(mapconcat 'identity '("one" "two" "three") "-")
--> "one-two-three"
 
(mapconcat (lambda (x) (concatenate 'string "[" x "]")) '("one" "two" "three") "
~")
--> "[one]~[two]~[three]"

 
Gauche Scheme:
 
(define (mapconcat fun lst sep)
  (reduce-right
    (^(a b)
      (apply string-append (map x->string (list a sep b))))
    ""
    (map fun lst)))
 
(mapconcat values '(one "two" three) '-)
  ===>
"one-two-three"
 
(mapconcat square '(2 3 4) '---)
  ===>
"4---9---16"