How to use global prefix command key in define mode-map key binding?

Question

I have a global prefix command key define like following:

(unless (boundp 'help-document-map)
  (define-prefix-command 'help-document-map))
;; (define-key my-programming-prefix-k (kbd "h") 'help-document-map)
(global-set-key (kbd "C-h d") 'help-document-map)

And then I want to use it in following mode-map defining keys.

(eval-after-load "helm-cscope"
  '(progn
     (define-key helm-cscope-mode-map (kbd "M-t") 'helm-cscope-find-symbol)
     (define-key helm-cscope-mode-map (kbd "M-r") 'helm-cscope-find-global-definition)
     (define-key helm-cscope-mode-map (kbd "M-g M-c") 'helm-cscope-find-called-function)
     (define-key helm-cscope-mode-map (kbd "M-g M-p") 'helm-cscope-find-calling-this-funtcion)
     (define-key helm-cscope-mode-map (kbd "M-s") 'helm-cscope-select)))

So how do I define this key binding?

Answer 1

It sounds like what you want is for C-h d to act as a prefix to a map dependent on the current mode.

There are a couple of solutions to this. One solution I have seen used in a couple of modes is to prefix each of the kbd calls with say help-document-prefix.

(defvar helm-document-prefix "C-h d")
(eval-after-load "helm-cscope"
  '(progn
     (define-key helm-cscope-mode-map 
                 (kbd (concat help-document-prefix " M-t")) 
                 'helm-cscope-find-symbol)))

This approach will enable C-h d M-t when helm-cscope-mode-map is active.

Another approach would be to set these bindings using local-set-key but inside of the mode hook. That would do a better job of respecting the help-document-prefix variable changing, as the binding would update every time the mode was enabled.

I don't know if there is a way to use a prefix map to dispatch to a function, which in turn dispatches to a keymap. It is possible to inherit from another keymap, but I don't know as that would help here.