RefTeX: How to modify the "select a reference format" menu?

Question

I use Emacs + RefTeX + AUCTeX to write .tex files. I use the handy keyboard macro

C-c )

for cross-references. This shows a menu named SELECT A REFERENCE FORMAT and I can choose between a number of options, such as \ref,\pageref and the like. However, among these I am missing the \eqref format. This leads to my question: How can I modify the SELECT A REFERENCE FORMAT menu to add \eqref?

Answer 1

The following works for me, though it may be imperfect as I'm not very comfortable with RefTeX customization:

(defun my-add-to-alist (alist-var key value &optional append)
  "Add an element to an association list.
If ALIST-VAR contains no element whose CAR is `equal' to KEY, then add
(KEY . VALUE) to ALIST-VAR. If APPEND is nil, add it to the beginning of
ALIST-VAR, otherwise add it to the end of ALIST-VAR.

If there is already an element in ALIST-VAR whose CAR is `equal' to KEY,
replace its CDR with VALUE."
  (interactive)
  (let ((cons-cell (assoc key (eval alist-var))))
    (if cons-cell
        (setcdr cons-cell value)
      (add-to-list alist-var (cons key value) append))))

(my-add-to-alist 'reftex-ref-style-alist
                 "AMSMath" '("amsmath" (("\\eqref" ?e))) t)

(require 'tex)
(TeX-add-style-hook "amsmath"
   #'(lambda ()
       (when (fboundp 'reftex-add-label-environments)
         (add-to-list 'reftex-ref-style-default-list "AMSMath" t)
         (reftex-ref-style-activate "AMSMath")
         (setq reftex-label-alist '(AMSTeX)))))

Note: I assume you already have something like this before the above code:

;; Use RefTeX in LaTeX buffers
(require 'reftex)
(add-hook 'LaTeX-mode-hook 'turn-on-reftex)   ; with AUCTeX's LaTeX mode
; (add-hook 'latex-mode-hook 'turn-on-reftex)   ; with Emacs' latex mode
(setq reftex-plug-into-AUCTeX t)