Using lisp code in query-replace-regexp

[Julien Cubizolles]

I can use the following replace string (for lack of a better term) with
query-replace-regexp

--8<---------------cut here---------------start------------->8---
\,(if (equal \2 nil) "+" (concat "+ " \2 " ::"))
--8<---------------cut here---------------end--------------->8---

How can I input it in a lisp function like:

--8<---------------cut here---------------start------------->8---
(defun jc-item-to-plus (Begin End)
  "Replace \\item by +"
  (interactive "r")
  (query-replace-regexp Begin End "some_standard_regexp" (if (equal \2 nil) "+" 
(concat "+ " \2 " ::")))
  )
--8<---------------cut here---------------end--------------->8---

Julien.