lisp/apropos.el

   1 ;;; apropos.el --- apropos commands for users and programmers.
   2
   3 ;; Copyright (C) 1989, 1994, 1995 Free Software Foundation, Inc.
   4
   5 ;; Author: Joe Wells <jbw@bigbird.bu.edu>
   6 ;; Rewritten: Daniel.Pfeiffer@Informatik.START.dbp.de, fax (+49 69) 7588-2389
   7 ;; Keywords: help
   8
   9 ;; This file is part of GNU Emacs.
  10
  11 ;; GNU Emacs is free software; you can redistribute it and/or modify
  12 ;; it under the terms of the GNU General Public License as published by
  13 ;; the Free Software Foundation; either version 2, or (at your option)
  14 ;; any later version.
  15
  16 ;; GNU Emacs is distributed in the hope that it will be useful,
  17 ;; but WITHOUT ANY WARRANTY; without even the implied warranty of
  18 ;; MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
  19 ;; GNU General Public License for more details.
  20
  21 ;; You should have received a copy of the GNU General Public License
  22 ;; along with GNU Emacs; see the file COPYING.  If not, write to the
  23 ;; Free Software Foundation, Inc., 59 Temple Place - Suite 330,
  24 ;; Boston, MA 02111-1307, USA.
  25
  26 ;;; Commentary:
  27
  28 ;; The ideas for this package were derived from the C code in
  29 ;; src/keymap.c and elsewhere.  The functions in this file should
  30 ;; always be byte-compiled for speed.  Someone should rewrite this in
  31 ;; C (as part of src/keymap.c) for speed.
  32
  33 ;; The idea for super-apropos is based on the original implementation
  34 ;; by Lynn Slater <lrs@esl.com>.
  35
  36 ;; History:
  37 ;; Fixed bug, current-local-map can return nil.
  38 ;; Change, doesn't calculate key-bindings unless needed.
  39 ;; Added super-apropos capability, changed print functions.
  40 ;;; Made fast-apropos and super-apropos share code.
  41 ;;; Sped up fast-apropos again.
  42 ;; Added apropos-do-all option.
  43 ;;; Added fast-command-apropos.
  44 ;; Changed doc strings to comments for helping functions.
  45 ;;; Made doc file buffer read-only, buried it.
  46 ;; Only call substitute-command-keys if do-all set.
  47
  48 ;; Optionally use configurable faces to make the output more legible.
  49 ;; Differentiate between command, function and macro.
  50 ;; Apropos-command (ex command-apropos) does cmd and optionally user var.
  51 ;; Apropos shows all 3 aspects of symbols (fn, var and plist)
  52 ;; Apropos-documentation (ex super-apropos) now finds all it should.
  53 ;; New apropos-value snoops through all values and optionally plists.
  54 ;; Reading DOC file doesn't load nroff.
  55 ;; Added hypertext following of documentation, mouse-2 on variable gives value
  56 ;;   from buffer in active window.
  57
  58 ;;; Code:
  59
  60 (defgroup apropos nil
  61   "Apropos commands for users and programmers"
  62   :group 'Help
  63   :prefix "apropos")
  64
  65 ;; I see a degradation of maybe 10-20% only.
  66 (defcustom apropos-do-all nil
  67   "*Whether the apropos commands should do more.
  68
  69 Slows them down more or less.  Set this non-nil if you have a fast machine."
  70   :group 'apropos
  71   :type 'boolean)
  72
  73
  74 (defcustom apropos-symbol-face (if window-system 'bold)
  75   "*Face for symbol name in apropos output or `nil'.
  76 This looks good, but slows down the commands several times."
  77   :group 'apropos
  78   :type 'face)
  79
  80 (defcustom apropos-keybinding-face (if window-system 'underline)
  81   "*Face for keybinding display in apropos output or `nil'.
  82 This looks good, but slows down the commands several times."
  83   :group 'apropos
  84   :type 'face)
  85
  86 (defcustom apropos-label-face (if window-system 'italic)
  87   "*Face for label (Command, Variable ...) in apropos output or `nil'.
  88 If this is `nil' no mouse highlighting occurs.
  89 This looks good, but slows down the commands several times.
  90 When this is a face name, as it is initially, it gets transformed to a
  91 text-property list for efficiency."
  92   :group 'apropos
  93   :type 'face)
  94
  95 (defcustom apropos-property-face (if window-system 'bold-italic)
  96   "*Face for property name in apropos output or `nil'.
  97 This looks good, but slows down the commands several times."
  98   :group 'apropos
  99   :type 'face)
 100
 101 (defcustom apropos-match-face (if window-system 'secondary-selection)
 102   "*Face for matching part in apropos-documentation/value output or `nil'.
 103 This looks good, but slows down the commands several times."
 104   :group 'apropos
 105   :type 'face)
 106
 107
 108 (defvar apropos-mode-map
 109   (let ((map (make-sparse-keymap)))
 110     (define-key map "\C-m" 'apropos-follow)
 111     (define-key map " "      'scroll-up)
 112     (define-key map "\177"   'scroll-down)
 113     (define-key map [mouse-2] 'apropos-mouse-follow)
 114     (define-key map [down-mouse-2] nil)
 115     map)
 116   "Keymap used in Apropos mode.")
 117
 118
 119 (defvar apropos-regexp nil
 120   "Regexp used in current apropos run.")
 121
 122 (defvar apropos-files-scanned ()
 123   "List of elc files already scanned in current run of `apropos-documentation'.")
 124
 125 (defvar apropos-accumulator ()
 126   "Alist of symbols already found in current apropos run.")
 127
 128 (defvar apropos-item ()
 129   "Current item in or for apropos-accumulator.")
 130 \f
 131 (defun apropos-mode ()
 132   "Major mode for following hyperlinks in output of apropos commands.
 133
 134 \\{apropos-mode-map}"
 135   (interactive)
 136   (kill-all-local-variables)
 137   (use-local-map apropos-mode-map)
 138   (setq major-mode 'apropos-mode
 139         mode-name "Apropos"))
 140
 141
 142 ;; For auld lang syne:
 143 ;;;###autoload
 144 (fset 'command-apropos 'apropos-command)
 145 ;;;###autoload
 146 (defun apropos-command (apropos-regexp &optional do-all)
 147   "Shows commands (interactively callable functions) that match REGEXP.
 148 With optional prefix ARG or if `apropos-do-all' is non-nil, also show
 149 variables."
 150   (interactive (list (read-string (concat "Apropos command "
 151                                           (if (or current-prefix-arg
 152                                                   apropos-do-all)
 153                                               "or variable ")
 154                                           "(regexp): "))
 155                      current-prefix-arg))
 156   (let ((message
 157          (let ((standard-output (get-buffer-create "*Apropos*")))
 158            (print-help-return-message 'identity))))
 159     (or do-all (setq do-all apropos-do-all))
 160     (setq apropos-accumulator
 161           (apropos-internal apropos-regexp
 162                             (if do-all
 163                                 (lambda (symbol) (or (commandp symbol)
 164                                                      (user-variable-p symbol)))
 165                               'commandp)))
 166     (if (apropos-print
 167          t
 168          (lambda (p)
 169            (let (doc symbol)
 170              (while p
 171                (setcar p (list
 172                           (setq symbol (car p))
 173                           (if (commandp symbol)
 174                               (if (setq doc (documentation symbol t))
 175                                   (substring doc 0 (string-match "\n" doc))
 176                                 "(not documented)"))
 177                           (and do-all
 178                                (user-variable-p symbol)
 179                                (if (setq doc (documentation-property
 180                                               symbol 'variable-documentation t))
 181                                    (substring doc 0
 182                                               (string-match "\n" doc))))))
 183                (setq p (cdr p)))))
 184          nil)
 185         (and message (message message)))))
 186
 187
 188 ;;;###autoload
 189 (defun apropos (apropos-regexp &optional do-all)
 190   "Show all bound symbols whose names match REGEXP.
 191 With optional prefix ARG or if `apropos-do-all' is non-nil, also show unbound
 192 symbols and key bindings, which is a little more time-consuming.
 193 Returns list of symbols and documentation found."
 194   (interactive "sApropos symbol (regexp): \nP")
 195   (setq apropos-accumulator
 196         (apropos-internal apropos-regexp
 197                           (and (not do-all)
 198                                (not apropos-do-all)
 199                                (lambda (symbol)
 200                                  (or (fboundp symbol)
 201                                      (boundp symbol)
 202                                      (facep symbol)
 203                                      (symbol-plist symbol))))))
 204   (apropos-print
 205    (or do-all apropos-do-all)
 206    (lambda (p)
 207      (let (symbol doc properties)
 208        (while p
 209          (setcar p (list
 210                     (setq symbol (car p))
 211                     (when (fboundp symbol)
 212                       (if (setq doc (documentation symbol t))
 213                           (substring doc 0 (string-match "\n" doc))
 214                         "(not documented)"))
 215                     (when (boundp symbol)
 216                       (if (setq doc (documentation-property
 217                                      symbol 'variable-documentation t))
 218                           (substring doc 0 (string-match "\n" doc))
 219                         "(not documented)"))
 220                     (when (setq properties (symbol-plist symbol))
 221                       (setq doc (list (car properties)))
 222                       (while (setq properties (cdr (cdr properties)))
 223                         (setq doc (cons (car properties) doc)))
 224                       (mapconcat #'symbol-name (nreverse doc) " "))
 225                     (when (get symbol 'widget-type)
 226                       (if (setq doc (documentation-property
 227                                      symbol 'widget-documentation t))
 228                           (substring doc 0
 229                                      (string-match "\n" doc))
 230                         "(not documented)"))
 231                     (when (facep symbol)
 232                       (if (setq doc (documentation-property
 233                                      symbol 'face-documentation t))
 234                           (substring doc 0
 235                                      (string-match "\n" doc))
 236                         "(not documented)"))
 237                     (when (get symbol 'custom-group)
 238                       (if (setq doc (documentation-property
 239                                      symbol 'group-documentation t))
 240                           (substring doc 0
 241                                      (string-match "\n" doc))
 242                         "(not documented)"))))
 243          (setq p (cdr p)))))
 244    nil))
 245
 246
 247 ;;;###autoload
 248 (defun apropos-value (apropos-regexp &optional do-all)
 249   "Show all symbols whose value's printed image matches REGEXP.
 250 With optional prefix ARG or if `apropos-do-all' is non-nil, also looks
 251 at the function and at the names and values of properties.
 252 Returns list of symbols and values found."
 253   (interactive "sApropos value (regexp): \nP")
 254   (or do-all (setq do-all apropos-do-all))
 255   (setq apropos-accumulator ())
 256    (let (f v p)
 257      (mapatoms
 258       (lambda (symbol)
 259         (setq f nil v nil p nil)
 260         (or (memq symbol '(apropos-regexp do-all apropos-accumulator
 261                                           symbol f v p))
 262             (setq v (apropos-value-internal 'boundp symbol 'symbol-value)))
 263         (if do-all
 264             (setq f (apropos-value-internal 'fboundp symbol 'symbol-function)
 265                   p (apropos-format-plist symbol "\n    " t)))
 266         (if (or f v p)
 267             (setq apropos-accumulator (cons (list symbol f v p)
 268                                             apropos-accumulator))))))
 269   (apropos-print nil nil t))
 270
 271
 272 ;;;###autoload
 273 (defun apropos-documentation (apropos-regexp &optional do-all)
 274   "Show symbols whose documentation contain matches for REGEXP.
 275 With optional prefix ARG or if `apropos-do-all' is non-nil, also use
 276 documentation that is not stored in the documentation file and show key
 277 bindings.
 278 Returns list of symbols and documentation found."
 279   (interactive "sApropos documentation (regexp): \nP")
 280   (or do-all (setq do-all apropos-do-all))
 281   (setq apropos-accumulator () apropos-files-scanned ())
 282   (let ((standard-input (get-buffer-create " apropos-temp"))
 283         f v)
 284     (unwind-protect
 285         (save-excursion
 286           (set-buffer standard-input)
 287           (apropos-documentation-check-doc-file)
 288           (if do-all
 289               (mapatoms
 290                (lambda (symbol)
 291                  (setq f (apropos-safe-documentation symbol)
 292                        v (get symbol 'variable-documentation))
 293                  (if (integerp v) (setq v))
 294                  (setq f (apropos-documentation-internal f)
 295                        v (apropos-documentation-internal v))
 296                  (if (or f v)
 297                      (if (setq apropos-item
 298                                (cdr (assq symbol apropos-accumulator)))
 299                          (progn
 300                            (if f
 301                                (setcar apropos-item f))
 302                            (if v
 303                                (setcar (cdr apropos-item) v)))
 304                        (setq apropos-accumulator
 305                              (cons (list symbol f v)
 306                                    apropos-accumulator)))))))
 307           (apropos-print nil nil t))
 308       (kill-buffer standard-input))))
 309
 310 \f
 311 (defun apropos-value-internal (predicate symbol function)
 312   (if (funcall predicate symbol)
 313       (progn
 314         (setq symbol (prin1-to-string (funcall function symbol)))
 315         (if (string-match apropos-regexp symbol)
 316             (progn
 317               (if apropos-match-face
 318                   (put-text-property (match-beginning 0) (match-end 0)
 319                                      'face apropos-match-face
 320                                      symbol))
 321               symbol)))))
 322
 323 (defun apropos-documentation-internal (doc)
 324   (if (consp doc)
 325       (apropos-documentation-check-elc-file (car doc))
 326     (and doc
 327          (string-match apropos-regexp doc)
 328          (progn
 329            (if apropos-match-face
 330                (put-text-property (match-beginning 0)
 331                                   (match-end 0)
 332                                   'face apropos-match-face
 333                                   (setq doc (copy-sequence doc))))
 334            doc))))
 335
 336 (defun apropos-format-plist (pl sep &optional compare)
 337   (setq pl (symbol-plist pl))
 338   (let (p p-out)
 339     (while pl
 340       (setq p (format "%s %S" (car pl) (nth 1 pl)))
 341       (if (or (not compare) (string-match apropos-regexp p))
 342           (if apropos-property-face
 343               (put-text-property 0 (length (symbol-name (car pl)))
 344                                  'face apropos-property-face p))
 345         (setq p nil))
 346       (if p
 347           (progn
 348             (and compare apropos-match-face
 349                  (put-text-property (match-beginning 0) (match-end 0)
 350                                     'face apropos-match-face
 351                                     p))
 352             (setq p-out (concat p-out (if p-out sep) p))))
 353       (setq pl (nthcdr 2 pl)))
 354     p-out))
 355
 356
 357 ;; Finds all documentation related to APROPOS-REGEXP in internal-doc-file-name.
 358
 359 (defun apropos-documentation-check-doc-file ()
 360   (let (type symbol (sepa 2) sepb beg end)
 361     (insert ?\^_)
 362     (backward-char)
 363     (insert-file-contents (concat doc-directory internal-doc-file-name))
 364     (forward-char)
 365     (while (save-excursion
 366              (setq sepb (search-forward "\^_"))
 367              (not (eobp)))
 368       (beginning-of-line 2)
 369       (if (save-restriction
 370             (narrow-to-region (point) (1- sepb))
 371             (re-search-forward apropos-regexp nil t))
 372           (progn
 373             (setq beg (match-beginning 0)
 374                   end (point))
 375             (goto-char (1+ sepa))
 376             (or (setq type (if (eq ?F (preceding-char))
 377                                1        ; function documentation
 378                              2)         ; variable documentation
 379                       symbol (read)
 380                       beg (- beg (point) 1)
 381                       end (- end (point) 1)
 382                       doc (buffer-substring (1+ (point)) (1- sepb))
 383                       apropos-item (assq symbol apropos-accumulator))
 384                 (setq apropos-item (list symbol nil nil)
 385                       apropos-accumulator (cons apropos-item
 386                                                 apropos-accumulator)))
 387             (if apropos-match-face
 388                 (put-text-property beg end 'face apropos-match-face doc))
 389             (setcar (nthcdr type apropos-item) doc)))
 390       (setq sepa (goto-char sepb)))))
 391
 392 (defun apropos-documentation-check-elc-file (file)
 393   (if (member file apropos-files-scanned)
 394       nil
 395     (let (symbol doc beg end this-is-a-variable)
 396       (setq apropos-files-scanned (cons file apropos-files-scanned))
 397       (erase-buffer)
 398       (insert-file-contents file)
 399       (while (search-forward "\n#@" nil t)
 400         ;; Read the comment length, and advance over it.
 401         (setq end (read)
 402               beg (1+ (point))
 403               end (+ (point) end -1))
 404         (forward-char)
 405         (if (save-restriction
 406               ;; match ^ and $ relative to doc string
 407               (narrow-to-region beg end)
 408               (re-search-forward apropos-regexp nil t))
 409             (progn
 410               (goto-char (+ end 2))
 411               (setq doc (buffer-substring beg end)
 412                     end (- (match-end 0) beg)
 413                     beg (- (match-beginning 0) beg)
 414                     this-is-a-variable (looking-at "(def\\(var\\|const\\) ")
 415                     symbol (progn
 416                              (skip-chars-forward "(a-z")
 417                              (forward-char)
 418                              (read))
 419                     symbol (if (consp symbol)
 420                                (nth 1 symbol)
 421                              symbol))
 422               (if (if this-is-a-variable
 423                       (get symbol 'variable-documentation)
 424                     (and (fboundp symbol) (apropos-safe-documentation symbol)))
 425                   (progn
 426                     (or (setq apropos-item (assq symbol apropos-accumulator))
 427                         (setq apropos-item (list symbol nil nil)
 428                               apropos-accumulator (cons apropos-item
 429                                                         apropos-accumulator)))
 430                     (if apropos-match-face
 431                         (put-text-property beg end 'face apropos-match-face
 432                                            doc))
 433                     (setcar (nthcdr (if this-is-a-variable 2 1)
 434                                     apropos-item)
 435                             doc)))))))))
 436
 437
 438
 439 (defun apropos-safe-documentation (function)
 440   "Like documentation, except it avoids calling `get_doc_string'.
 441 Will return nil instead."
 442   (while (and function (symbolp function))
 443     (setq function (if (fboundp function)
 444                        (symbol-function function))))
 445   (if (eq (car-safe function) 'macro)
 446       (setq function (cdr function)))
 447   (setq function (if (byte-code-function-p function)
 448                      (if (> (length function) 4)
 449                          (aref function 4))
 450                    (if (eq (car-safe function) 'autoload)
 451                        (nth 2 function)
 452                      (if (eq (car-safe function) 'lambda)
 453                          (if (stringp (nth 2 function))
 454                              (nth 2 function)
 455                            (if (stringp (nth 3 function))
 456                                (nth 3 function)))))))
 457   (if (integerp function)
 458       nil
 459     function))
 460
 461
 462
 463 (defun apropos-print (do-keys doc-fn spacing)
 464   "Output result of various apropos commands with `apropos-regexp'.
 465 APROPOS-ACCUMULATOR is a list.  Optional DOC-FN is called for each element
 466 of apropos-accumulator and may modify it resulting in (symbol fn-doc
 467 var-doc [plist-doc]).  Returns sorted list of symbols and documentation
 468 found."
 469   (if (null apropos-accumulator)
 470       (message "No apropos matches for `%s'" apropos-regexp)
 471     (if doc-fn
 472         (funcall doc-fn apropos-accumulator))
 473     (setq apropos-accumulator
 474           (sort apropos-accumulator (lambda (a b)
 475                                       (string-lessp (car a) (car b)))))
 476     (and apropos-label-face
 477          (symbolp apropos-label-face)
 478          (setq apropos-label-face `(face ,apropos-label-face
 479                                          mouse-face highlight)))
 480     (with-output-to-temp-buffer "*Apropos*"
 481       (let ((p apropos-accumulator)
 482             (old-buffer (current-buffer))
 483             symbol item point1 point2)
 484         (set-buffer standard-output)
 485         (apropos-mode)
 486         (if window-system
 487             (insert "If you move the mouse over text that changes color,\n"
 488                     (substitute-command-keys
 489                      "you can click \\[apropos-mouse-follow] to get more information.\n")))
 490         (insert (substitute-command-keys
 491                  "In this buffer, type \\[apropos-follow] to get full documentation.\n\n"))
 492         (while (consp p)
 493           (or (not spacing) (bobp) (terpri))
 494           (setq apropos-item (car p)
 495                 symbol (car apropos-item)
 496                 p (cdr p)
 497                 point1 (point))
 498           (princ symbol)                        ; print symbol name
 499           (setq point2 (point))
 500           ;; Calculate key-bindings if we want them.
 501           (and do-keys
 502                (commandp symbol)
 503                (indent-to 30 1)
 504                (if (let ((keys
 505                           (save-excursion
 506                             (set-buffer old-buffer)
 507                             (where-is-internal symbol)))
 508                          filtered)
 509                      ;; Copy over the list of key sequences,
 510                      ;; omitting any that contain a buffer or a frame.
 511                      (while keys
 512                        (let ((key (car keys))
 513                              (i 0)
 514                              loser)
 515                          (while (< i (length key))
 516                            (if (or (framep (aref key i))
 517                                    (bufferp (aref key i)))
 518                                (setq loser t))
 519                            (setq i (1+ i)))
 520                          (or loser
 521                              (setq filtered (cons key filtered))))
 522                        (setq keys (cdr keys)))
 523                      (setq item filtered))
 524                    ;; Convert the remaining keys to a string and insert.
 525                    (insert
 526                     (mapconcat
 527                      (lambda (key)
 528                        (setq key (key-description key))
 529                        (if apropos-keybinding-face
 530                            (put-text-property 0 (length key)
 531                                               'face apropos-keybinding-face
 532                                               key))
 533                        key)
 534                      item ", "))
 535                  (insert "M-x")
 536                  (put-text-property (- (point) 3) (point)
 537                                     'face apropos-keybinding-face)
 538                  (insert " " (symbol-name symbol) " ")
 539                  (insert "RET")
 540                  (put-text-property (- (point) 3) (point)
 541                                     'face apropos-keybinding-face)))
 542           (terpri)
 543           ;; only now so we don't propagate text attributes all over
 544           (put-text-property point1 point2 'item
 545                              (if (eval `(or ,@(cdr apropos-item)))
 546                                  (car apropos-item)
 547                                apropos-item))
 548           (if apropos-symbol-face
 549               (put-text-property point1 point2 'face apropos-symbol-face))
 550           (apropos-print-doc 'describe-function 1
 551                              (if (commandp symbol)
 552                                  "Command"
 553                                (if (apropos-macrop symbol)
 554                                    "Macro"
 555                                  "Function"))
 556                              do-keys)
 557           (if (get symbol 'custom-type)
 558               (apropos-print-doc 'customize-variable-other-window 2
 559                                  "User Option" do-keys)
 560             (apropos-print-doc 'describe-variable 2
 561                                "Variable" do-keys))
 562           (apropos-print-doc 'customize-group-other-window 6 "Group" do-keys)
 563           (apropos-print-doc 'customize-face-other-window 5 "Face" do-keys)
 564           (apropos-print-doc 'widget-browse-other-window 4 "Widget" do-keys)
 565           (apropos-print-doc 'apropos-describe-plist 3
 566                              "Plist" nil)))))
 567   (prog1 apropos-accumulator
 568     (setq apropos-accumulator ())))     ; permit gc
 569
 570
 571 (defun apropos-macrop (symbol)
 572   "T if SYMBOL is a Lisp macro."
 573   (and (fboundp symbol)
 574        (consp (setq symbol
 575                     (symbol-function symbol)))
 576        (or (eq (car symbol) 'macro)
 577            (if (eq (car symbol) 'autoload)
 578                (memq (nth 4 symbol)
 579                      '(macro t))))))
 580
 581
 582 (defun apropos-print-doc (action i str do-keys)
 583   (if (stringp (setq i (nth i apropos-item)))
 584       (progn
 585         (insert "  ")
 586         (put-text-property (- (point) 2) (1- (point))
 587                            'action action)
 588         (insert str ": ")
 589         (if apropos-label-face
 590             (add-text-properties (- (point) (length str) 2)
 591                                  (1- (point))
 592                                  apropos-label-face))
 593         (insert (if do-keys (substitute-command-keys i) i))
 594         (or (bolp) (terpri)))))
 595
 596
 597 (defun apropos-mouse-follow (event)
 598   (interactive "e")
 599   (let ((other (if (eq (current-buffer) (get-buffer "*Apropos*"))
 600                    ()
 601                  (current-buffer))))
 602     (save-excursion
 603       (set-buffer (window-buffer (posn-window (event-start event))))
 604       (goto-char (posn-point (event-start event)))
 605       (or (and (not (eobp)) (get-text-property (point) 'mouse-face))
 606           (and (not (bobp)) (get-text-property (1- (point)) 'mouse-face))
 607           (error "There is nothing to follow here"))
 608       (apropos-follow other))))
 609
 610
 611 (defun apropos-follow (&optional other)
 612   (interactive)
 613   (let* (;; Properties are always found at the beginning of the line.
 614          (bol (save-excursion (beginning-of-line) (point)))
 615          ;; If there is no `item' property here, look behind us.
 616          (item (get-text-property bol 'item))
 617          (item-at (if item nil (previous-single-property-change bol 'item)))
 618          ;; Likewise, if there is no `action' property here, look in front.
 619          (action (get-text-property bol 'action))
 620          (action-at (if action nil (next-single-property-change bol 'action))))
 621     (and (null item) item-at
 622          (setq item (get-text-property (1- item-at) 'item)))
 623     (and (null action) action-at
 624          (setq action (get-text-property action-at 'action)))
 625     (if (not (and item action))
 626         (error "There is nothing to follow here"))
 627     (if (consp item) (error "There is nothing to follow in `%s'" (car item)))
 628     (if other (set-buffer other))
 629     (funcall action item)))
 630
 631
 632
 633 (defun apropos-describe-plist (symbol)
 634   "Display a pretty listing of SYMBOL's plist."
 635   (with-output-to-temp-buffer "*Help*"
 636     (set-buffer standard-output)
 637     (princ "Symbol ")
 638     (prin1 symbol)
 639     (princ "'s plist is\n (")
 640     (if apropos-symbol-face
 641         (put-text-property 8 (- (point) 14) 'face apropos-symbol-face))
 642     (insert (apropos-format-plist symbol "\n  "))
 643     (princ ")")
 644     (print-help-return-message)))
 645
 646 (provide 'apropos)
 647
 648 ;;; apropos.el ends here