replace variable winum-keymap-prefix with function winum-set-keymap-prefix

Fixes #1.

Setting the key bindings prefix using a variable just couldn't work given how
Emacs handles key bindings for minor modes and that the available keymap API
doesn't handle keymaps.

README.org

@@ -95,16 +95,23 @@ Emacs configuration:
 
 * Configuration
 ** Keybindings
-By default, all key bindings are prefixed with a value stored in
+The default prefix for key bindings is ~C-x w~ for compatibility with native
-=winum-keymap-prefix=, by default ~C-x w~. See [[#customize-options][Customize options]].
+Emacs bindings.
 
-The default prefix is ~C-x w~ for compatibility with native Emacs bindings.
+If you don't like ~C-x w~, you can set a prefix of your choosing using the
-However, it gives long key bindings and can be incomfortable to use.
+function =winum-set-keymap-prefix=:
 
-For instance, you could replace the native prefix with ~C-c~ or ~M-m~.
+#+BEGIN_SRC elisp
+  (winum-set-keymap-prefix (kbd "C-c"))
+#+END_SRC
 
-If you prefer no to use a prefix to have even shorter bindings, you can also
+This function overrides the value of =winum-keymap=, so you should call it
-directly override =winum-keymap=:
+before customization of =winum-keymap= and/or after customization of
+=winum-base-map=. Its argument must be a key sequence, like the ones returned by
+=kbd=.
+
+If you prefer no to use a prefix and have even shorter bindings, you can also
+override =winum-keymap= in the minor mode bindings table:
 
 #+BEGIN_SRC emacs-lisp
   (require 'winum)
@@ -127,13 +134,16 @@ directly override =winum-keymap=:
   (winum-mode)
 #+END_SRC
 
-This is a little bit hacky but is less code than using =define-key=, and will
+You can also use the more conventional =define-key= on =winum-keymap=:
-also shadow the old bindings.
 
-*NB:* Both ~`~ and ~²~ are mapped to =winum-select-window-by-number= to handle
+#+BEGIN_SRC emacs-lisp
-      both =qwerty= and =azerty= keyboard layouts.
+  (define-key winum-keymap (kbd "C-x y o l o") 'winum-select-window-by-number)
-      If you are using a different kind of layout, the recommended place to map
+#+END_SRC
-      it is the key beside ~1~.
+
+*NB:* Both ~`~ and ~²~ are mapped to =winum-select-window-by-number= by default
+      to handle both =qwerty= and =azerty= keyboard layouts. If you are using a
+      different kind of layout, the recommended place to map it is the key
+      beside ~1~.
 
 ** Customize options
 Several options are available through Emacs' Customize interface under
@@ -205,12 +215,6 @@ Several options are available through Emacs' Customize interface under
 
   Default: '(" *which-key*")
 
-- =winum-keymap-prefix=
-
-  Prefix key sequence for keybindings.
-
-  Default: =(kbd "C-x w")=
-
 - face: =winum-face=
 
   Face used for the number in the mode-line.
@@ -220,8 +224,6 @@ Here is an example that you could put in your =.emacs=, which includes all
 available winum options.
 
 #+BEGIN_SRC emacs-lisp
-  (add-to-list 'load-path "/path/to/install/folder/winum.el/")
-
   (require 'winum)
 
   (setcdr (assoc 'winum-mode minor-mode-map-alist)
@@ -256,8 +258,7 @@ available winum options.
         winum-assign-func                 'my-winum-assign-func
         winum-auto-setup-mode-line        t
         winum-mode-line-position          1
-        winum-ignored-buffers             '(" *which-key*")
+        winum-ignored-buffers             '(" *which-key*"))
-        winum-keymap-prefix               nil)
 
   (winum-mode)
 #+END_SRC

winum.el

@@ -111,33 +111,30 @@ numbers in the mode-line.")
   :group 'winum
   :type  '(repeat string))
 
-(defcustom winum-keymap-prefix (kbd "C-x w")
-  "Prefix key sequence for keybindings."
-  :group 'winum
-  :type  'string)
-
 (defface winum-face '()
   "Face used for the number in the mode-line."
   :group 'winum)
 
-(defvar winum-keymap
+(defvar winum-base-map
-  (when winum-keymap-prefix
+  (let ((map (make-sparse-keymap)))
-    (let ((map (make-sparse-keymap)))
+    (define-key map (kbd "`") 'winum-select-window-by-number)
-      (let ((prefix-map (make-sparse-keymap)))
+    (define-key map (kbd "²") 'winum-select-window-by-number)
-        (define-key prefix-map (kbd "`") 'winum-select-window-by-number)
+    (define-key map (kbd "0") 'winum-select-window-0-or-10)
-        (define-key prefix-map (kbd "²") 'winum-select-window-by-number)
+    (define-key map (kbd "1") 'winum-select-window-1)
-        (define-key prefix-map (kbd "0") 'winum-select-window-0-or-10)
+    (define-key map (kbd "2") 'winum-select-window-2)
-        (define-key prefix-map (kbd "1") 'winum-select-window-1)
+    (define-key map (kbd "3") 'winum-select-window-3)
-        (define-key prefix-map (kbd "2") 'winum-select-window-2)
+    (define-key map (kbd "4") 'winum-select-window-4)
-        (define-key prefix-map (kbd "3") 'winum-select-window-3)
+    (define-key map (kbd "5") 'winum-select-window-5)
-        (define-key prefix-map (kbd "4") 'winum-select-window-4)
+    (define-key map (kbd "6") 'winum-select-window-6)
-        (define-key prefix-map (kbd "5") 'winum-select-window-5)
+    (define-key map (kbd "7") 'winum-select-window-7)
-        (define-key prefix-map (kbd "6") 'winum-select-window-6)
+    (define-key map (kbd "8") 'winum-select-window-8)
-        (define-key prefix-map (kbd "7") 'winum-select-window-7)
+    (define-key map (kbd "9") 'winum-select-window-9)
-        (define-key prefix-map (kbd "8") 'winum-select-window-8)
+    map)
-        (define-key prefix-map (kbd "9") 'winum-select-window-9)
+  "Keymap to be used under the prefix provided by `winum-keymap-prefix'.")
-        (define-key map winum-keymap-prefix prefix-map))
+
-      map))
+(defvar winum-keymap (let ((map (make-sparse-keymap)))
+                       (define-key map (kbd "C-x w") winum-base-map)
+                       map)
   "Keymap used for `winum-mode'.")
 
 ;; Internal variables ----------------------------------------------------------
@@ -281,7 +278,7 @@ There are several ways to provide the number:
   (interactive "P")
   (let* ((n (cond
              ((integerp arg) arg)
-             ((eq arg '-) 0) ; negative-argument
+             ((eq arg '-) 0) ; the negative argument
              (arg (winum-get-number))
              ((called-interactively-p 'any)
               (let ((user-input-str (read-from-minibuffer "Window: ")))
@@ -301,6 +298,19 @@ There are several ways to provide the number:
 
 ;; Public API ------------------------------------------------------------------
 
+;;;###autoload
+(defun winum-set-keymap-prefix (prefix)
+  "Set key bindings prefix for `winum-keymap' based on `winum-base-map'.
+This function overrides the value of `winum-keymap', so you
+should call it before customization of `winum-keymap' and/or
+after customization of `winum-base-map'.
+PREFIX must be a key sequence, like the ones returned by `kbd'."
+  (setq winum-keymap (when prefix (let ((map (make-sparse-keymap)))
+                                    (define-key map prefix winum-base-map)
+                                    map)))
+  (setcdr (assoc 'winum-mode minor-mode-map-alist)
+          winum-keymap))
+
 ;;;###autoload
 (defun winum-get-window-by-number (n)
   "Return window numbered N if exists, nil otherwise."