lisp/ielm.el

   1 ;;; ielm.el --- interaction mode for Emacs Lisp
   2
   3 ;; Copyright (C) 1994, 2001-2011 Free Software Foundation, Inc.
   4
   5 ;; Author: David Smith <maa036@lancaster.ac.uk>
   6 ;; Maintainer: FSF
   7 ;; Created: 25 Feb 1994
   8 ;; Keywords: lisp
   9
  10 ;; This file is part of GNU Emacs.
  11
  12 ;; GNU Emacs is free software: you can redistribute it and/or modify
  13 ;; it under the terms of the GNU General Public License as published by
  14 ;; the Free Software Foundation, either version 3 of the License, or
  15 ;; (at your option) any later version.
  16
  17 ;; GNU Emacs is distributed in the hope that it will be useful,
  18 ;; but WITHOUT ANY WARRANTY; without even the implied warranty of
  19 ;; MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
  20 ;; GNU General Public License for more details.
  21
  22 ;; You should have received a copy of the GNU General Public License
  23 ;; along with GNU Emacs.  If not, see <http://www.gnu.org/licenses/>.
  24
  25 ;;; Commentary:
  26
  27 ;; Provides a nice interface to evaluating Emacs Lisp expressions.
  28 ;; Input is handled by the comint package, and output is passed
  29 ;; through the pretty-printer.
  30
  31 ;; To start: M-x ielm.  Type C-h m in the *ielm* buffer for more info.
  32
  33 ;;; Code:
  34
  35 (require 'comint)
  36 (require 'pp)
  37
  38 ;;; User variables
  39
  40 (defgroup ielm nil
  41   "Interaction mode for Emacs Lisp."
  42   :group 'lisp)
  43
  44
  45 (defcustom ielm-noisy t
  46   "If non-nil, IELM will beep on error."
  47   :type 'boolean
  48   :group 'ielm)
  49
  50 (defcustom ielm-prompt-read-only t
  51   "If non-nil, the IELM prompt is read only.
  52 The read only region includes the newline before the prompt.
  53 Setting this variable does not affect existing IELM runs.
  54 This works by setting the buffer-local value of `comint-prompt-read-only'.
  55 Setting that value directly affects new prompts in the current buffer.
  56
  57 If this option is enabled, then the safe way to temporarily
  58 override the read-only-ness of IELM prompts is to call
  59 `comint-kill-whole-line' or `comint-kill-region' with no
  60 narrowing in effect.  This way you will be certain that none of
  61 the remaining prompts will be accidentally messed up.  You may
  62 wish to put something like the following in your `.emacs' file:
  63
  64 \(add-hook 'ielm-mode-hook
  65           '(lambda ()
  66              (define-key ielm-map \"\\C-w\" 'comint-kill-region)
  67              (define-key ielm-map [C-S-backspace]
  68                'comint-kill-whole-line)))
  69
  70 If you set `comint-prompt-read-only' to t, you might wish to use
  71 `comint-mode-hook' and `comint-mode-map' instead of
  72 `ielm-mode-hook' and `ielm-map'.  That will affect all comint
  73 buffers, including IELM buffers.  If you sometimes use IELM on
  74 text-only terminals or with `emacs -nw', you might wish to use
  75 another binding for `comint-kill-whole-line'."
  76   :type 'boolean
  77   :group 'ielm
  78   :version "22.1")
  79
  80 (defcustom ielm-prompt "ELISP> "
  81   "Prompt used in IELM.
  82 Setting this variable does not affect existing IELM runs.
  83
  84 Interrupting the IELM process with \\<ielm-map>\\[comint-interrupt-subjob],
  85 and then restarting it using \\[ielm], makes the then current
  86 default value affect _new_ prompts.  Unless the new prompt
  87 differs only in text properties from the old one, IELM will no
  88 longer recognize the old prompts.  However, executing \\[ielm]
  89 does not update the prompt of an *ielm* buffer with a running process.
  90 For IELM buffers that are not called `*ielm*', you can execute
  91 \\[inferior-emacs-lisp-mode] in that IELM buffer to update the value,
  92 for new prompts.  This works even if the buffer has a running process."
  93   :type 'string
  94   :group 'ielm)
  95
  96 (defvar ielm-prompt-internal "ELISP> "
  97   "Stored value of `ielm-prompt' in the current IELM buffer.
  98 This is an internal variable used by IELM.  Its purpose is to
  99 prevent a running IELM process from being messed up when the user
 100 customizes `ielm-prompt'.")
 101
 102 (defcustom ielm-dynamic-return t
 103   "Controls whether \\<ielm-map>\\[ielm-return] has intelligent behavior in IELM.
 104 If non-nil, \\[ielm-return] evaluates input for complete sexps, or inserts a newline
 105 and indents for incomplete sexps.  If nil, always inserts newlines."
 106   :type 'boolean
 107   :group 'ielm)
 108
 109 (defcustom ielm-dynamic-multiline-inputs t
 110   "Force multiline inputs to start from column zero?
 111 If non-nil, after entering the first line of an incomplete sexp, a newline
 112 will be inserted after the prompt, moving the input to the next line.
 113 This gives more frame width for large indented sexps, and allows functions
 114 such as `edebug-defun' to work with such inputs."
 115   :type 'boolean
 116   :group 'ielm)
 117
 118 (defcustom ielm-mode-hook nil
 119   "Hooks to be run when IELM (`inferior-emacs-lisp-mode') is started."
 120   :options '(turn-on-eldoc-mode)
 121   :type 'hook
 122   :group 'ielm)
 123 (defvaralias 'inferior-emacs-lisp-mode-hook 'ielm-mode-hook)
 124
 125 (defvar * nil
 126   "Most recent value evaluated in IELM.")
 127
 128 (defvar ** nil
 129   "Second-most-recent value evaluated in IELM.")
 130
 131 (defvar *** nil
 132   "Third-most-recent value evaluated in IELM.")
 133
 134 (defvar ielm-match-data nil
 135   "Match data saved at the end of last command.")
 136
 137 (defvar *1 nil
 138   "During IELM evaluation, most recent value evaluated in IELM.
 139 Normally identical to `*'.  However, if the working buffer is an IELM
 140 buffer, distinct from the process buffer, then `*' gives the value in
 141 the working buffer, `*1' the value in the process buffer.
 142 The intended value is only accessible during IELM evaluation.")
 143
 144 (defvar *2 nil
 145   "During IELM evaluation, second-most-recent value evaluated in IELM.
 146 Normally identical to `**'.  However, if the working buffer is an IELM
 147 buffer, distinct from the process buffer, then `**' gives the value in
 148 the working buffer, `*2' the value in the process buffer.
 149 The intended value is only accessible during IELM evaluation.")
 150
 151 (defvar *3 nil
 152   "During IELM evaluation, third-most-recent value evaluated in IELM.
 153 Normally identical to `***'.  However, if the working buffer is an IELM
 154 buffer, distinct from the process buffer, then `***' gives the value in
 155 the working buffer, `*3' the value in the process buffer.
 156 The intended value is only accessible during IELM evaluation.")
 157
 158 ;;; System variables
 159
 160 (defvar ielm-working-buffer nil
 161   "Buffer in which IELM sexps will be evaluated.
 162 This variable is buffer-local.")
 163
 164 (defvar ielm-header
 165   "*** Welcome to IELM ***  Type (describe-mode) for help.\n"
 166   "Message to display when IELM is started.")
 167
 168 (defvar ielm-map
 169   (let ((map (make-sparse-keymap)))
 170     (define-key map "\t" 'comint-dynamic-complete)
 171     (define-key map "\C-m" 'ielm-return)
 172     (define-key map "\C-j" 'ielm-send-input)
 173     (define-key map "\e\C-x" 'eval-defun)         ; for consistency with
 174     (define-key map "\e\t" 'completion-at-point)  ; lisp-interaction-mode
 175     ;; These bindings are from `lisp-mode-shared-map' -- can you inherit
 176     ;; from more than one keymap??
 177     (define-key map "\e\C-q" 'indent-sexp)
 178     (define-key map "\177" 'backward-delete-char-untabify)
 179     ;; Some convenience bindings for setting the working buffer
 180     (define-key map "\C-c\C-b" 'ielm-change-working-buffer)
 181     (define-key map "\C-c\C-f" 'ielm-display-working-buffer)
 182     (define-key map "\C-c\C-v" 'ielm-print-working-buffer)
 183     map)
 184   "Keymap for IELM mode.")
 185 (defvaralias 'inferior-emacs-lisp-mode-map 'ielm-map)
 186
 187 (defvar ielm-font-lock-keywords
 188   '(("\\(^\\*\\*\\*[^*]+\\*\\*\\*\\)\\(.*$\\)"
 189      (1 font-lock-comment-face)
 190      (2 font-lock-constant-face)))
 191   "Additional expressions to highlight in IELM buffers.")
 192
 193 ;;; Completion stuff
 194
 195 (defun ielm-tab nil
 196   "Possibly indent the current line as Lisp code."
 197   (interactive)
 198   (when (or (eq (preceding-char) ?\n)
 199             (eq (char-syntax (preceding-char)) ?\s))
 200     (ielm-indent-line)
 201     t))
 202
 203 (defun ielm-complete-symbol nil
 204   "Complete the Lisp symbol before point."
 205   ;; A wrapper for lisp-complete symbol that returns non-nil if
 206   ;; completion has occurred
 207   (let* ((btick (buffer-modified-tick))
 208          (cbuffer (get-buffer "*Completions*"))
 209          (ctick (and cbuffer (buffer-modified-tick cbuffer))))
 210     (lisp-complete-symbol)
 211      ;; completion has occurred if:
 212     (or
 213      ;; the buffer has been modified
 214      (not (= btick (buffer-modified-tick)))
 215      ;; a completions buffer has been modified or created
 216      (if cbuffer
 217          (not (= ctick (buffer-modified-tick cbuffer)))
 218        (get-buffer "*Completions*")))))
 219
 220 (defun ielm-complete-filename nil
 221   "Dynamically complete filename before point, if in a string."
 222   (when (nth 3 (parse-partial-sexp comint-last-input-start (point)))
 223     (comint-dynamic-complete-filename)))
 224
 225 (defun ielm-indent-line nil
 226   "Indent the current line as Lisp code if it is not a prompt line."
 227   (when (save-excursion (comint-bol) (bolp))
 228     (lisp-indent-line)))
 229
 230 ;;; Working buffer manipulation
 231
 232 (defun ielm-print-working-buffer nil
 233   "Print the current IELM working buffer's name in the echo area."
 234   (interactive)
 235   (message "The current working buffer is: %s" (buffer-name ielm-working-buffer)))
 236
 237 (defun ielm-display-working-buffer nil
 238   "Display the current IELM working buffer.
 239 Don't forget that selecting that buffer will change its value of `point'
 240 to its value of `window-point'!"
 241   (interactive)
 242   (display-buffer ielm-working-buffer)
 243   (ielm-print-working-buffer))
 244
 245 (defun ielm-change-working-buffer (buf)
 246   "Change the current IELM working buffer to BUF.
 247 This is the buffer in which all sexps entered at the IELM prompt are
 248 evaluated.  You can achieve the same effect with a call to
 249 `set-buffer' at the IELM prompt."
 250   (interactive "bSet working buffer to: ")
 251   (let ((buffer (get-buffer buf)))
 252     (if (and buffer (buffer-live-p buffer))
 253         (setq ielm-working-buffer buffer)
 254       (error "No such buffer: %S" buf)))
 255   (ielm-print-working-buffer))
 256
 257 ;;; Other bindings
 258
 259 (defun ielm-return nil
 260   "Newline and indent, or evaluate the sexp before the prompt.
 261 Complete sexps are evaluated; for incomplete sexps inserts a newline
 262 and indents.  If however `ielm-dynamic-return' is nil, this always
 263 simply inserts a newline."
 264   (interactive)
 265   (if ielm-dynamic-return
 266       (let ((state
 267              (save-excursion
 268                (end-of-line)
 269                (parse-partial-sexp (ielm-pm)
 270                                    (point)))))
 271         (if (and (< (car state) 1) (not (nth 3 state)))
 272             (ielm-send-input)
 273           (when (and ielm-dynamic-multiline-inputs
 274                      (save-excursion
 275                        (beginning-of-line)
 276                        (looking-at-p comint-prompt-regexp)))
 277             (save-excursion
 278               (goto-char (ielm-pm))
 279               (newline 1)))
 280           (newline-and-indent)))
 281     (newline)))
 282
 283 (defvar ielm-input)
 284
 285 (defun ielm-input-sender (proc input)
 286   ;; Just sets the variable ielm-input, which is in the scope of
 287   ;; `ielm-send-input's call.
 288   (setq ielm-input input))
 289
 290 (defun ielm-send-input nil
 291   "Evaluate the Emacs Lisp expression after the prompt."
 292   (interactive)
 293   (let (ielm-input)                     ; set by ielm-input-sender
 294     (comint-send-input)                 ; update history, markers etc.
 295     (ielm-eval-input ielm-input)))
 296
 297 ;;; Utility functions
 298
 299 (defun ielm-is-whitespace-or-comment (string)
 300   "Return non-nil if STRING is all whitespace or a comment."
 301   (or (string= string "")
 302       (string-match-p "\\`[ \t\n]*\\(?:;.*\\)*\\'" string)))
 303
 304 ;;; Evaluation
 305
 306 (defun ielm-eval-input (ielm-string)
 307   "Evaluate the Lisp expression IELM-STRING, and pretty-print the result."
 308   ;; This is the function that actually `sends' the input to the
 309   ;; `inferior Lisp process'. All comint-send-input does is works out
 310   ;; what that input is.  What this function does is evaluates that
 311   ;; input and produces `output' which gets inserted into the buffer,
 312   ;; along with a new prompt.  A better way of doing this might have
 313   ;; been to actually send the output to the `cat' process, and write
 314   ;; this as in output filter that converted sexps in the output
 315   ;; stream to their evaluated value.  But that would have involved
 316   ;; more process coordination than I was happy to deal with.
 317   ;;
 318   ;; NOTE: all temporary variables in this function will be in scope
 319   ;; during the eval, and so need to have non-clashing names.
 320   (let (ielm-form                       ; form to evaluate
 321         ielm-pos                        ; End posn of parse in string
 322         ielm-result                     ; Result, or error message
 323         ielm-error-type                 ; string, nil if no error
 324         (ielm-output "")                ; result to display
 325         (ielm-wbuf ielm-working-buffer) ; current buffer after evaluation
 326         (ielm-pmark (ielm-pm)))
 327     (unless (ielm-is-whitespace-or-comment ielm-string)
 328       (condition-case err
 329           (let ((rout (read-from-string ielm-string)))
 330             (setq ielm-form (car rout)
 331                   ielm-pos (cdr rout)))
 332         (error (setq ielm-result (error-message-string err))
 333                (setq ielm-error-type "Read error")))
 334       (unless ielm-error-type
 335         ;; Make sure working buffer has not been killed
 336         (if (not (buffer-name ielm-working-buffer))
 337             (setq ielm-result "Working buffer has been killed"
 338                   ielm-error-type "IELM Error"
 339                   ielm-wbuf (current-buffer))
 340           (if (ielm-is-whitespace-or-comment (substring ielm-string ielm-pos))
 341               ;; To correctly handle the ielm-local variables *,
 342               ;; ** and ***, we need a temporary buffer to be
 343               ;; current at entry to the inner of the next two let
 344               ;; forms.  We need another temporary buffer to exit
 345               ;; that same let.  To avoid problems, neither of
 346               ;; these buffers should be alive during the
 347               ;; evaluation of ielm-form.
 348               (let ((*1 *)
 349                     (*2 **)
 350                     (*3 ***)
 351                     ielm-temp-buffer)
 352                 (set-match-data ielm-match-data)
 353                 (save-excursion
 354                   (with-temp-buffer
 355                     (condition-case err
 356                         (unwind-protect
 357                              ;; The next let form creates default
 358                              ;; bindings for *, ** and ***.  But
 359                              ;; these default bindings are
 360                              ;; identical to the ielm-local
 361                              ;; bindings.  Hence, during the
 362                              ;; evaluation of ielm-form, the
 363                              ;; ielm-local values are going to be
 364                              ;; used in all buffers except for
 365                              ;; other ielm buffers, which override
 366                              ;; them.  Normally, the variables *1,
 367                              ;; *2 and *3 also have default
 368                              ;; bindings, which are not overridden.
 369                              (let ((* *1)
 370                                    (** *2)
 371                                    (*** *3))
 372                                (kill-buffer (current-buffer))
 373                                (set-buffer ielm-wbuf)
 374                                (setq ielm-result
 375                                      (eval ielm-form lexical-binding))
 376                                (setq ielm-wbuf (current-buffer))
 377                                (setq
 378                                 ielm-temp-buffer
 379                                 (generate-new-buffer " *ielm-temp*"))
 380                                (set-buffer ielm-temp-buffer))
 381                           (when ielm-temp-buffer
 382                             (kill-buffer ielm-temp-buffer)))
 383                       (error (setq ielm-result (error-message-string err))
 384                              (setq ielm-error-type "Eval error"))
 385                       (quit (setq ielm-result "Quit during evaluation")
 386                             (setq ielm-error-type "Eval error")))))
 387                 (setq ielm-match-data (match-data)))
 388             (setq ielm-error-type "IELM error")
 389             (setq ielm-result "More than one sexp in input"))))
 390
 391       ;; If the eval changed the current buffer, mention it here
 392       (unless (eq ielm-wbuf ielm-working-buffer)
 393         (message "current buffer is now: %s" ielm-wbuf)
 394         (setq ielm-working-buffer ielm-wbuf))
 395
 396       (goto-char ielm-pmark)
 397       (unless ielm-error-type
 398         (condition-case err
 399             ;; Self-referential objects cause loops in the printer, so
 400             ;; trap quits here. May as well do errors, too
 401             (setq ielm-output (concat ielm-output (pp-to-string ielm-result)))
 402           (error (setq ielm-error-type "IELM Error")
 403                  (setq ielm-result "Error during pretty-printing (bug in pp)"))
 404           (quit  (setq ielm-error-type "IELM Error")
 405                  (setq ielm-result "Quit during pretty-printing"))))
 406       (if ielm-error-type
 407           (progn
 408             (when ielm-noisy (ding))
 409             (setq ielm-output (concat ielm-output "*** " ielm-error-type " ***  "))
 410             (setq ielm-output (concat ielm-output ielm-result)))
 411         ;; There was no error, so shift the *** values
 412         (setq *** **)
 413         (setq ** *)
 414         (setq * ielm-result))
 415       (setq ielm-output (concat ielm-output "\n")))
 416     (setq ielm-output (concat ielm-output ielm-prompt-internal))
 417     (comint-output-filter (ielm-process) ielm-output)))
 418
 419 ;;; Process and marker utilities
 420
 421 (defun ielm-process nil
 422   ;; Return the current buffer's process.
 423   (get-buffer-process (current-buffer)))
 424
 425 (defun ielm-pm nil
 426   ;; Return the process mark of the current buffer.
 427   (process-mark (get-buffer-process (current-buffer))))
 428
 429 (defun ielm-set-pm (pos)
 430   ;; Set the process mark in the current buffer to POS.
 431   (set-marker (process-mark (get-buffer-process (current-buffer))) pos))
 432
 433 ;;; Major mode
 434
 435 (define-derived-mode inferior-emacs-lisp-mode comint-mode "IELM"
 436   "Major mode for interactively evaluating Emacs Lisp expressions.
 437 Uses the interface provided by `comint-mode' (which see).
 438
 439 * \\<ielm-map>\\[ielm-send-input] evaluates the sexp following the prompt.  There must be at most
 440   one top level sexp per prompt.
 441
 442 * \\[ielm-return] inserts a newline and indents, or evaluates a
 443   complete expression (but see variable `ielm-dynamic-return').
 444   Inputs longer than one line are moved to the line following the
 445   prompt (but see variable `ielm-dynamic-multiline-inputs').
 446
 447 * \\[comint-dynamic-complete] completes Lisp symbols (or filenames, within strings),
 448   or indents the line if there is nothing to complete.
 449
 450 The current working buffer may be changed (with a call to `set-buffer',
 451 or with \\[ielm-change-working-buffer]), and its value is preserved between successive
 452 evaluations.  In this way, expressions may be evaluated in a different
 453 buffer than the *ielm* buffer.  By default, its name is shown on the
 454 mode line; you can always display it with \\[ielm-print-working-buffer], or the buffer itself
 455 with \\[ielm-display-working-buffer].
 456
 457 During evaluations, the values of the variables `*', `**', and `***'
 458 are the results of the previous, second previous and third previous
 459 evaluations respectively.  If the working buffer is another IELM
 460 buffer, then the values in the working buffer are used.  The variables
 461 `*1', `*2' and `*3', yield the process buffer values.
 462
 463 Expressions evaluated by IELM are not subject to `debug-on-quit' or
 464 `debug-on-error'.
 465
 466 The behavior of IELM may be customized with the following variables:
 467 * To stop beeping on error, set `ielm-noisy' to nil.
 468 * If you don't like the prompt, you can change it by setting `ielm-prompt'.
 469 * If you do not like that the prompt is (by default) read-only, set
 470   `ielm-prompt-read-only' to nil.
 471 * Set `ielm-dynamic-return' to nil for bindings like `lisp-interaction-mode'.
 472 * Entry to this mode runs `comint-mode-hook' and `ielm-mode-hook'
 473  (in that order).
 474
 475 Customized bindings may be defined in `ielm-map', which currently contains:
 476 \\{ielm-map}"
 477   :syntax-table emacs-lisp-mode-syntax-table
 478
 479   (setq comint-prompt-regexp (concat "^" (regexp-quote ielm-prompt)))
 480   (set (make-local-variable 'paragraph-separate) "\\'")
 481   (set (make-local-variable 'paragraph-start) comint-prompt-regexp)
 482   (setq comint-input-sender 'ielm-input-sender)
 483   (setq comint-process-echoes nil)
 484   (set (make-local-variable 'comint-dynamic-complete-functions)
 485        '(ielm-tab comint-replace-by-expanded-history
 486          ielm-complete-filename ielm-complete-symbol))
 487   (set (make-local-variable 'ielm-prompt-internal) ielm-prompt)
 488   (set (make-local-variable 'comint-prompt-read-only) ielm-prompt-read-only)
 489   (setq comint-get-old-input 'ielm-get-old-input)
 490   (set (make-local-variable 'comint-completion-addsuffix) '("/" . ""))
 491   (setq mode-line-process '(":%s on " (:eval (buffer-name ielm-working-buffer))))
 492
 493   (set (make-local-variable 'indent-line-function) 'ielm-indent-line)
 494   (set (make-local-variable 'ielm-working-buffer) (current-buffer))
 495   (set (make-local-variable 'fill-paragraph-function) 'lisp-fill-paragraph)
 496   (add-hook 'completion-at-point-functions
 497             'lisp-completion-at-point nil 'local)
 498
 499   ;; Value holders
 500   (set (make-local-variable '*) nil)
 501   (set (make-local-variable '**) nil)
 502   (set (make-local-variable '***) nil)
 503   (set (make-local-variable 'ielm-match-data) nil)
 504
 505   ;; font-lock support
 506   (set (make-local-variable 'font-lock-defaults)
 507        '(ielm-font-lock-keywords nil nil ((?: . "w") (?- . "w") (?* . "w"))))
 508
 509   ;; A dummy process to keep comint happy. It will never get any input
 510   (unless (comint-check-proc (current-buffer))
 511     ;; Was cat, but on non-Unix platforms that might not exist, so
 512     ;; use hexl instead, which is part of the Emacs distribution.
 513     (condition-case nil
 514         (start-process "ielm" (current-buffer) "hexl")
 515       (file-error (start-process "ielm" (current-buffer) "cat")))
 516     (set-process-query-on-exit-flag (ielm-process) nil)
 517     (goto-char (point-max))
 518
 519     ;; Lisp output can include raw characters that confuse comint's
 520     ;; carriage control code.
 521     (set (make-local-variable 'comint-inhibit-carriage-motion) t)
 522
 523     ;; Add a silly header
 524     (insert ielm-header)
 525     (ielm-set-pm (point-max))
 526     (unless comint-use-prompt-regexp
 527       (let ((inhibit-read-only t))
 528         (add-text-properties
 529          (point-min) (point-max)
 530          '(rear-nonsticky t field output inhibit-line-move-field-capture t))))
 531     (comint-output-filter (ielm-process) ielm-prompt-internal)
 532     (set-marker comint-last-input-start (ielm-pm))
 533     (set-process-filter (get-buffer-process (current-buffer)) 'comint-output-filter)))
 534
 535 (defun ielm-get-old-input nil
 536   ;; Return the previous input surrounding point
 537   (save-excursion
 538     (beginning-of-line)
 539     (unless (looking-at-p comint-prompt-regexp)
 540       (re-search-backward comint-prompt-regexp))
 541     (comint-skip-prompt)
 542     (buffer-substring (point) (progn (forward-sexp 1) (point)))))
 543
 544 ;;; User command
 545
 546 ;;;###autoload (add-hook 'same-window-buffer-names (purecopy "*ielm*"))
 547
 548 ;;;###autoload
 549 (defun ielm nil
 550   "Interactively evaluate Emacs Lisp expressions.
 551 Switches to the buffer `*ielm*', or creates it if it does not exist."
 552   (interactive)
 553   (let (old-point)
 554     (unless (comint-check-proc "*ielm*")
 555       (with-current-buffer (get-buffer-create "*ielm*")
 556         (unless (zerop (buffer-size)) (setq old-point (point)))
 557         (inferior-emacs-lisp-mode)))
 558     (pop-to-buffer "*ielm*")
 559     (when old-point (push-mark old-point))))
 560
 561 (provide 'ielm)
 562
 563 ;;; ielm.el ends here