How do I add a keybinding to use during an interactive isearch, `C-s ...`

Question

Can I assign a key binding starting with C-s such as:

(global-set-key (kbd "C-s C-w") 'isearch-forward-symbol-at-point)

but I want to keep (kbd "C-s") for i-search.

---

I am having following error:

error: Key sequence C-s C-w starts with non-prefix key C-s

To ensure normal operation, you should investigate and remove the
cause of the error in your initialization file.  Start Emacs with
the ‘--debug-init’ option to view a complete error backtrace.

Answer 1

As I understand your question, you want C-s to start an interactive search, as it normally does, but if you press C-w after you've started that search, you want it to switch to isearch-symbol-at-point.

First off, the feature you're after is almost the same as the default behaviour bound to C-s C-M-w. That will call isearch-yank-symbol-or-char, which is close, but not identical to isearch-symbol-at-point. Maybe that's close enough.

If you really want to call isearch-forward-symbol-at-point, without overwriting the default behaviour of C-s, you'll need to add the new binding to the isearch-mode-map:

(define-key isearch-mode-map (kbd "C-w")
  'isearch-forward-symbol-at-point)

Note that this will overwrite the default definition of C-s C-w, which is to call the function isearch-yank-word-or-char.

The default options to isearch are described in the manual (info "(emacs) Isearch Yank")

Answer 2

The C-s needs to be assigned as a prefix command.

eg

(define-prefix-command 'myprefix)
(global-set-key (kbd "C-s") 'myprefix)
(global-set-key (kbd "C-s C-s") 'helm-occur)