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[gnu-emacs] / lisp / help.el

;; Help commands for Emacs
;; Copyright (C) 1985, 1986 Free Software Foundation, Inc.

;; This file is part of GNU Emacs.

;; GNU Emacs is free software; you can redistribute it and/or modify
;; it under the terms of the GNU General Public License as published by
;; the Free Software Foundation; either version 1, or (at your option)
;; any later version.

;; GNU Emacs is distributed in the hope that it will be useful,
;; but WITHOUT ANY WARRANTY; without even the implied warranty of
;; MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
;; GNU General Public License for more details.

;; You should have received a copy of the GNU General Public License
;; along with GNU Emacs; see the file COPYING.  If not, write to
;; the Free Software Foundation, 675 Mass Ave, Cambridge, MA 02139, USA.

;;;###autoload
(defvar help-map (make-sparse-keymap)
  "Keymap for characters following the Help key.")

(define-key global-map "\C-h" 'help-command)
(fset 'help-command help-map)

(define-key help-map "\C-h" 'help-for-help)
(define-key help-map "?" 'help-for-help)

(define-key help-map "\C-c" 'describe-copying)
(define-key help-map "\C-d" 'describe-distribution)
(define-key help-map "\C-w" 'describe-no-warranty)
(define-key help-map "a" 'command-apropos)

(define-key help-map "b" 'describe-bindings)

(define-key help-map "c" 'describe-key-briefly)
(define-key help-map "k" 'describe-key)

(define-key help-map "d" 'describe-function)
(define-key help-map "f" 'describe-function)

(define-key help-map "i" 'info)

(define-key help-map "l" 'view-lossage)

(define-key help-map "m" 'describe-mode)

(define-key help-map "\C-n" 'view-emacs-news)
(define-key help-map "n" 'view-emacs-news)

(define-key help-map "s" 'describe-syntax)

(define-key help-map "t" 'help-with-tutorial)

(define-key help-map "w" 'where-is)

(define-key help-map "v" 'describe-variable)

(defun help-with-tutorial ()
  "Select the Emacs learn-by-doing tutorial."
  (interactive)
  (let ((file (expand-file-name "~/TUTORIAL")))
    (delete-other-windows)
    (if (get-file-buffer file)
        (switch-to-buffer (get-file-buffer file))
      (switch-to-buffer (create-file-buffer file))
      (setq buffer-file-name file)
      (setq default-directory (expand-file-name "~/"))
      (setq auto-save-file-name nil)
      (insert-file-contents (expand-file-name "TUTORIAL" exec-directory))
      (goto-char (point-min))
      (search-forward "\n<<")
      (beginning-of-line)
      (delete-region (point) (progn (end-of-line) (point)))
      (newline (- (window-height (selected-window))
                  (count-lines (point-min) (point))
                  6))
      (goto-char (point-min))
      (set-buffer-modified-p nil))))

(defun describe-key-briefly (key)
  "Print the name of the function KEY invokes.  KEY is a string."
  (interactive "kDescribe key briefly: ")
  (let ((defn (key-binding key)))
    (if (or (null defn) (integerp defn))
        (message "%s is undefined" (key-description key))
      (message "%s runs the command %s"
               (key-description key)
               (if (symbolp defn) defn (prin1-to-string defn))))))

(defun print-help-return-message (&optional function)
  "Display or return message saying how to restore windows after help command.
Computes a message and applies the optional argument FUNCTION to it.
If FUNCTION is nil, applies `message' to it, thus printing it."
  (and (not (get-buffer-window standard-output))
       (funcall (or function 'message)
                (concat
                 (substitute-command-keys
                  (if (one-window-p t)
                      (if pop-up-windows
                          "Type \\[delete-other-windows] to remove help window."
                        "Type \\[switch-to-buffer] RET to remove help window.")
                    "Type \\[switch-to-buffer-other-window] RET to restore the other window."))
                 (substitute-command-keys
                  "  \\[scroll-other-window] to scroll the help.")))))

(defun describe-key (key)
  "Display documentation of the function invoked by KEY.  KEY is a string."
  (interactive "kDescribe key: ")
  (let ((defn (key-binding key)))
    (if (or (null defn) (integerp defn))
        (message "%s is undefined" (key-description key))
      (with-output-to-temp-buffer "*Help*"
        (prin1 defn)
        (princ ":\n")
        (if (documentation defn)
            (princ (documentation defn))
          (princ "not documented"))
        (print-help-return-message)))))

(defun describe-mode (&optional minor)
  "Display documentation of current major mode.
If optional MINOR is non-nil (or prefix argument is given if interactive),
display documentation of active minor modes as well.
For this to work correctly for a minor mode, the mode's indicator variable
(listed in `minor-mode-alist') must also be a function whose documentation
describes the minor mode."
  (interactive)
  (with-output-to-temp-buffer "*Help*"
    (princ mode-name)
    (princ " Mode:\n")
    (princ (documentation major-mode))
    (let ((minor-modes minor-mode-alist)
          (locals (buffer-local-variables)))
      (while minor-modes
        (let* ((minor-mode (car (car minor-modes)))
               (indicator (car (cdr (car minor-modes))))
               (local-binding (assq minor-mode locals)))
          ;; Document a minor mode if it is listed in minor-mode-alist,
          ;; bound locally in this buffer, non-nil, and has a function
          ;; definition.
          (if (and local-binding
                   (cdr local-binding)
                   (fboundp minor-mode))
              (progn
                (princ (format "\n\n\n%s minor mode (indicator%s):\n"
                               minor-mode indicator))
                (princ (documentation minor-mode)))))
        (setq minor-modes (cdr minor-modes))))
    (print-help-return-message)))

;; So keyboard macro definitions are documented correctly
(fset 'defining-kbd-macro (symbol-function 'start-kbd-macro))

(defun describe-distribution ()
  "Display info on how to obtain the latest version of GNU Emacs."
  (interactive)
  (find-file-read-only
   (expand-file-name "DISTRIB" exec-directory)))

(defun describe-copying ()
  "Display info on how you may redistribute copies of GNU Emacs."
  (interactive)
  (find-file-read-only
   (expand-file-name "COPYING" exec-directory))
  (goto-char (point-min)))

(defun describe-no-warranty ()
  "Display info on all the kinds of warranty Emacs does NOT have."
  (interactive)
  (describe-copying)
  (let (case-fold-search)
    (search-forward "NO WARRANTY")
    (recenter 0)))

(defun view-emacs-news ()
  "Display info on recent changes to Emacs."
  (interactive)
  (find-file-read-only (expand-file-name "NEWS" exec-directory)))

(defun view-lossage ()
  "Display last 100 input keystrokes."
  (interactive)
  (with-output-to-temp-buffer "*Help*"
    (princ (key-description (recent-keys)))
    (save-excursion
      (set-buffer standard-output)
      (goto-char (point-min))
      (while (progn (move-to-column 50) (not (eobp)))
        (search-forward " " nil t)
        (insert "\n")))
    (print-help-return-message)))

(defun help-for-help ()
  "You have typed C-h, the help character.  Type a Help option:

A  command-apropos.   Give a substring, and see a list of commands
              (functions interactively callable) that contain
              that substring.  See also the  apropos  command.
B  describe-bindings.  Display table of all key bindings.
C  describe-key-briefly.  Type a command key sequence;
              it prints the function name that sequence runs.
F  describe-function.  Type a function name and get documentation of it.
I  info. The  info  documentation reader.
K  describe-key.  Type a command key sequence;
              it displays the full documentation.
L  view-lossage.  Shows last 100 characters you typed.
M  describe-mode.  Print documentation of current major mode,
              which describes the commands peculiar to it.
N  view-emacs-news.  Shows emacs news file.
S  describe-syntax.  Display contents of syntax table, plus explanations
T  help-with-tutorial.  Select the Emacs learn-by-doing tutorial.
V  describe-variable.  Type name of a variable;
              it displays the variable's documentation and value.
W  where-is.  Type command name; it prints which keystrokes
              invoke that command.
C-c print Emacs copying permission (General Public License).
C-d print Emacs ordering information.
C-n print news of recent Emacs changes.
C-w print information on absence of warranty for GNU Emacs."
  (interactive)
  (message
 "A B C F I K L M N S T V W C-c C-d C-n C-w.  Type C-h again for more help: ")
  (let ((char (read-char)))
    (if (or (= char ?\C-h) (= char ??))
        (save-window-excursion
          (switch-to-buffer "*Help*")
          (delete-other-windows)
          (erase-buffer)
          (insert (documentation 'help-for-help))
          (goto-char (point-min))
          (while (memq char '(?\C-h ?? ?\C-v ?\  ?\177 ?\M-v))
            (if (memq char '(?\C-v ?\ ))
                (scroll-up))
            (if (memq char '(?\177 ?\M-v))
                (scroll-down))
            (message "A B C F I K L M N S T V W C-c C-d C-n C-w%s: "
                     (if (pos-visible-in-window-p (point-max))
                         "" " or Space to scroll"))
            (let ((cursor-in-echo-area t))
              (setq char (read-char))))))
    (let ((defn (cdr (assq (downcase char) (cdr help-map)))))
      (if defn (call-interactively defn) (ding)))))


;; Return a function which is called by the list containing point.
;; If that gives no function, return a function whose name is around point.
;; If that doesn't give a function, return nil.
(defun function-called-at-point ()
  (or (condition-case ()
          (save-excursion
            (save-restriction
              (narrow-to-region (max (point-min) (- (point) 1000)) (point-max))
              (backward-up-list 1)
              (forward-char 1)
              (let (obj)
                (setq obj (read (current-buffer)))
                (and (symbolp obj) (fboundp obj) obj))))
        (error nil))
      (condition-case ()
          (save-excursion
            (forward-sexp -1)
            (skip-chars-forward "'")
            (let ((obj (read (current-buffer))))
              (and (symbolp obj) (fboundp obj) obj)))
        (error nil))))

(defun describe-function (function)
  "Display the full documentation of FUNCTION (a symbol)."
  (interactive
   (let ((fn (function-called-at-point))
         (enable-recursive-minibuffers t)            
         val)
     (setq val (completing-read (if fn
                                    (format "Describe function (default %s): " fn)
                                  "Describe function: ")
                                obarray 'fboundp t))
     (list (if (equal val "")
               fn (intern val)))))
  (with-output-to-temp-buffer "*Help*"
    (prin1 function)
    (princ ": ")
    (let* ((def (symbol-function function))
           (beg (if (commandp def) "an interactive " "a ")))
      (princ (cond ((stringp def) "a keyboard macro.")
                   ((subrp def)
                    (concat beg "built-in function."))
                   ((compiled-function-p def)
                    (concat beg "compiled Lisp function."))
                   ((symbolp def)
                    (format "alias for `%s'." def))
                   ((eq (car-safe def) 'lambda)
                    (concat beg "Lisp function."))
                   ((eq (car-safe def) 'macro)
                    "a Lisp macro.")
                   ((eq (car-safe def) 'mocklisp)
                    "a mocklisp function.")
                   ((eq (car-safe def) 'autoload)
                    (format "%sLisp %s to autoload from `%s'."
                            beg
                            (if (nth 4 def) "macro" "function")
                            (nth 1 def)))
                   (t "")))
      (terpri))
    (if (documentation function)
        (princ (documentation function))
      (princ "not documented"))
    (print-help-return-message)
    ;; Return the text we displayed.
    (save-excursion (set-buffer standard-output) (buffer-string))))

(defun variable-at-point ()
  (condition-case ()
      (save-excursion
        (forward-sexp -1)
        (skip-chars-forward "'")
        (let ((obj (read (current-buffer))))
          (and (symbolp obj) (boundp obj) obj)))
    (error nil)))

(defun describe-variable (variable)
  "Display the full documentation of VARIABLE (a symbol).
Returns the documentation as a string, also."
  (interactive 
   (let ((v (variable-at-point))
         (enable-recursive-minibuffers t)
         val)
     (setq val (completing-read (if v
                                    (format "Describe variable (default %s): " v)
                                  "Describe variable: ")
                                obarray 'boundp t))
     (list (if (equal val "")
               v (intern val)))))
  (with-output-to-temp-buffer "*Help*"
    (prin1 variable)
    (princ "'s value is ")
    (if (not (boundp variable))
        (princ "void.")
      (prin1 (symbol-value variable)))
    (terpri) (terpri)
    (princ "Documentation:")
    (terpri)
    (let ((doc (documentation-property variable 'variable-documentation)))
      (if doc
          (princ (substitute-command-keys doc))
        (princ "not documented as a variable.")))
    (print-help-return-message)
    ;; Return the text we displayed.
    (save-excursion (set-buffer standard-output) (buffer-string))))

(defun command-apropos (string)
  "Like apropos but lists only symbols that are names of commands
\(interactively callable functions).  Argument REGEXP is a regular expression
that is matched against command symbol names.  Returns list of symbols and
documentation found."
  (interactive "sCommand apropos (regexp): ")
  (let ((message
         (let ((standard-output (get-buffer-create "*Help*")))
           (print-help-return-message 'identity))))
    (apropos string 'commandp)
    (and message (message message))))

(defun locate-library (library &optional nosuffix)
  "Show the full path name of Emacs library LIBRARY.
This command searches the directories in `load-path' like `M-x load-library'
to find the file that `M-x load-library RET LIBRARY RET' would load.
Optional second arg NOSUFFIX non-nil means don't add suffixes `.elc' or `.el'
to the specified name LIBRARY (a la calling `load' instead of `load-library')."
  (interactive "sLocate library: ")
  (catch 'answer
    (mapcar
     '(lambda (dir)
        (mapcar
         '(lambda (suf)
            (let ((try (expand-file-name (concat library suf) dir)))
              (and (file-readable-p try)
                   (null (file-directory-p try))
                   (progn
                     (message "Library is file %s" try)
                     (throw 'answer try)))))
         (if nosuffix '("") '(".elc" ".el" ""))))
     load-path)
    (message "No library %s in search path" library)
    nil))