Commit 61e56e2c authored by Juanma Barranquero's avatar Juanma Barranquero

lisp/simple.el (alternatives-define): New macro.

etc/NEWS: Document new "generic commands" support.
parent 3323c263
2013-07-06 Juanma Barranquero <>
* NEWS: Document new "generic commands" support.
2013-06-27 Juanma Barranquero <>
* NEWS: Document new Desktop option `desktop-save-windows'.
......@@ -133,6 +133,10 @@ monitor, use the new functions above. Similar notes also apply to
`x-display-pixel-width', `x-display-pixel-height', `display-mm-width',
`display-mm-height', `x-display-mm-width', and `x-display-mm-height'.
** New macro `alternatives-define' can be used to define generic commands.
Generic commands are interactive functions whose implementation can be
selected among several alternatives, as a matter of user preference.
* Editing Changes in Emacs 24.4
2013-07-06 Juanma Barranquero <>
* simple.el (alternatives-define): New macro.
2013-07-06 Stefan Monnier <>
* subr.el (read-quoted-char): Use read-key.
......@@ -7346,6 +7346,67 @@ warning using STRING as the message.")
(with-eval-after-load pkg
(bad-package-check pkg))))
;;; Generic dispatcher commands
;; Macro `alternatives-define' is used to create generic commands.
;; Generic commands are these (like web, mail, news, encrypt, irc, etc.)
;; that can have different alternative implementations where choosing
;; among them is exclusively a matter of user preference.
;; (alternatives-define COMMAND) creates a new interactive command
;; M-x COMMAND and a customizable variable COMMAND-alternatives.
;; Typically, the user will not need to customize this variable; packages
;; wanting to add alternative implementations should use
;; ;;;###autoload (push '("My impl name" . my-impl-symbol) COMMAND-alternatives
(defmacro alternatives-define (command &rest customizations)
"Define new command `COMMAND'.
The variable `COMMAND-alternatives' will contain alternative
implementations of COMMAND, so that running `C-u M-x COMMAND'
will allow the user to chose among them.
CUSTOMIZATIONS, if non-nil, should be composed of alternating
`defcustom' keywords and values to add to the declaration of
`COMMAND-alternatives' (typically to add new groups)."
(let* ((command-name (symbol-name command))
(varalt-name (concat command-name "-alternatives"))
(varalt-sym (intern varalt-name))
(varimp-sym (intern (concat command-name "--implementation"))))
(defcustom ,varalt-sym nil
,(format "Alist of alternative implementations for the `%s' command.
Each entry must be a pair (ALTNAME . ALTFUN), where:
ALTNAME - The name shown at user to describe the alternative implementation.
ALTFUN - The function called to implement this alternative."
:type '(alist :key-type string :value-type function)
:group 'dispatcher
(defvar ,varimp-sym nil "Internal use only.")
(defun ,command (&optional arg)
,(format "Run generic command `%s'.
If used for the first time, or with interactive ARG, ask the user which
implementation to use for `%s'. The variable `%s'
contains the list of implementations currently supported for this command."
command-name command-name varalt-name)
(interactive "P")
(when (or arg (null ,varimp-sym))
(let ((val (completing-read
,(format "Select implementation for command `%s': " command-name)
,varalt-sym nil t)))
(unless (string-equal val "")
(customize-save-variable ',varimp-sym
(cdr (assoc-string val ,varalt-sym))))))
(if ,varimp-sym
(funcall ,varimp-sym)
(message ,(format "No implementation selected for command `%s'"
(provide 'simple)
;;; simple.el ends here
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