lisp/progmodes/xscheme.el

   1 ;;; xscheme.el --- run MIT Scheme under Emacs        -*- lexical-binding: t; -*-
   2
   3 ;; Copyright (C) 1986-1987, 1989-1990, 2001-2017 Free Software
   4 ;; Foundation, Inc.
   5
   6 ;; Maintainer: emacs-devel@gnu.org
   7 ;; Keywords: languages, lisp
   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 3 of the License, or
  14 ;; (at your option) 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.  If not, see <http://www.gnu.org/licenses/>.
  23
  24 ;;; Commentary:
  25
  26 ;; A major mode for interacting with MIT Scheme.
  27 ;;
  28 ;; Requires MIT Scheme release 5 or later.
  29 ;; Changes to Control-G handler require runtime version 13.85 or later.
  30
  31 ;;; Code:
  32
  33 (require 'scheme)
  34
  35 ;;;; Internal Variables
  36
  37 (defvar xscheme-previous-mode)
  38 (defvar xscheme-last-input-end)
  39
  40 (defvar xscheme-process-command-line nil
  41   "Command used to start the most recent Scheme process.")
  42
  43 (defvar xscheme-process-name "scheme"
  44   "Name of xscheme process that we're currently interacting with.")
  45
  46 (defvar xscheme-buffer-name "*scheme*"
  47   "Name of xscheme buffer that we're currently interacting with.")
  48
  49 (defvar xscheme-expressions-ring-max 30
  50   "Maximum length of Scheme expressions ring.")
  51
  52 (defvar-local xscheme-expressions-ring nil
  53   "List of expressions recently transmitted to the Scheme process.")
  54
  55 (defvar-local xscheme-expressions-ring-yank-pointer nil
  56   "The tail of the Scheme expressions ring whose car is the last thing yanked.")
  57
  58 (defvar-local xscheme-running-p nil
  59   "This variable, if nil, indicates that the scheme process is
  60 waiting for input.  Otherwise, it is busy evaluating something.")
  61
  62 (defconst xscheme-control-g-synchronization-p t
  63   "If non-nil, insert markers in the scheme input stream to indicate when
  64 control-g interrupts were signaled.  Do not allow more control-g's to be
  65 signaled until the scheme process acknowledges receipt.")
  66
  67 (defvar-local xscheme-control-g-disabled-p nil
  68   "This variable, if non-nil, indicates that a control-g is being processed
  69 by the scheme process, so additional control-g's are to be ignored.")
  70
  71 (defvar xscheme-string-receiver nil
  72   "Procedure to send the string argument from the scheme process.")
  73
  74 (defconst default-xscheme-runlight
  75   '(": " xscheme-runlight-string)
  76   "Default global (shared) xscheme-runlight mode line format.")
  77
  78 (defvar xscheme-runlight "")
  79 (defvar xscheme-runlight-string nil)
  80
  81 (defvar-local xscheme-process-filter-state 'idle
  82   "State of scheme process escape reader state machine:
  83 idle                   waiting for an escape sequence
  84 reading-type           received an altmode but nothing else
  85 reading-string         reading prompt string")
  86
  87 (defvar-local xscheme-allow-output-p t
  88   "This variable, if nil, prevents output from the scheme process
  89 from being inserted into the process-buffer.")
  90
  91 (defvar-local xscheme-prompt ""
  92   "The current scheme prompt string.")
  93
  94 (defvar-local xscheme-string-accumulator ""
  95   "Accumulator for the string being received from the scheme process.")
  96
  97 (defvar-local xscheme-mode-string nil)
  98 (setq-default scheme-mode-line-process '("" xscheme-runlight))
  99 (make-variable-buffer-local 'scheme-mode-line-process)
 100
 101 \f
 102 (defgroup xscheme nil
 103   "Major mode for editing Scheme and interacting with MIT's C-Scheme."
 104   :group 'lisp)
 105
 106 (defcustom scheme-band-name nil
 107   "Band loaded by the `run-scheme' command."
 108   :type '(choice (const nil) string)
 109   :group 'xscheme)
 110
 111 (defcustom scheme-program-arguments nil
 112   "Arguments passed to the Scheme program by the `run-scheme' command."
 113   :type '(choice (const nil) string)
 114   :group 'xscheme)
 115
 116 (defcustom xscheme-allow-pipelined-evaluation t
 117   "If non-nil, an expression may be transmitted while another is evaluating.
 118 Otherwise, attempting to evaluate an expression before the previous expression
 119 has finished evaluating will signal an error."
 120   :type 'boolean
 121   :group 'xscheme)
 122
 123 (defcustom xscheme-startup-message
 124   "This is the Scheme process buffer.
 125 Type \\[xscheme-send-previous-expression] to evaluate the expression before point.
 126 Type \\[xscheme-send-control-g-interrupt] to abort evaluation.
 127 Type \\[describe-mode] for more information.
 128
 129 "
 130   "String to insert into Scheme process buffer first time it is started.
 131 Is processed with `substitute-command-keys' first."
 132   :type 'string
 133   :group 'xscheme)
 134
 135 (defcustom xscheme-signal-death-message nil
 136   "If non-nil, causes a message to be generated when the Scheme process dies."
 137   :type 'boolean
 138   :group 'xscheme)
 139
 140 (defcustom xscheme-start-hook nil
 141   "If non-nil, a procedure to call when the Scheme process is started.
 142 When called, the current buffer will be the Scheme process-buffer."
 143   :type 'hook
 144   :group 'xscheme
 145   :version "20.3")
 146
 147 (defun xscheme-evaluation-commands (keymap)
 148   (define-key keymap "\e\C-x" 'xscheme-send-definition)
 149   (define-key keymap "\C-x\C-e" 'xscheme-send-previous-expression)
 150   (put 'xscheme-send-previous-expression :advertised-binding "\C-x\C-e")
 151   (define-key keymap "\eo" 'xscheme-send-buffer)
 152   (define-key keymap "\ez" 'xscheme-send-definition)
 153   (define-key keymap "\e\C-m" 'xscheme-send-previous-expression)
 154   (define-key keymap "\e\C-z" 'xscheme-send-region))
 155
 156 (defun xscheme-interrupt-commands (keymap)
 157   (define-key keymap "\C-c\C-s" 'xscheme-select-process-buffer)
 158   (define-key keymap "\C-c\C-b" 'xscheme-send-breakpoint-interrupt)
 159   (define-key keymap "\C-c\C-c" 'xscheme-send-control-g-interrupt)
 160   (define-key keymap "\C-c\C-u" 'xscheme-send-control-u-interrupt)
 161   (define-key keymap "\C-c\C-x" 'xscheme-send-control-x-interrupt))
 162
 163 (xscheme-evaluation-commands scheme-mode-map)
 164 (xscheme-interrupt-commands scheme-mode-map)
 165 \f
 166 (defun run-scheme (command-line)
 167   "Run MIT Scheme in an inferior process.
 168 Output goes to the buffer `*scheme*'.
 169 With argument, asks for a command line."
 170   (interactive (list (xscheme-read-command-line current-prefix-arg)))
 171   (xscheme-start command-line xscheme-process-name xscheme-buffer-name))
 172
 173 (defun xscheme-start (command-line process-name buffer-name)
 174   (setq-default xscheme-process-command-line command-line)
 175   (switch-to-buffer
 176    (xscheme-start-process command-line process-name buffer-name))
 177   (set (make-local-variable 'xscheme-process-command-line) command-line))
 178
 179 (defun xscheme-read-command-line (arg)
 180   (let ((default
 181           (or xscheme-process-command-line
 182               (xscheme-default-command-line))))
 183     (if arg
 184         (read-string "Run Scheme: " default)
 185         default)))
 186
 187 (defun xscheme-default-command-line ()
 188   (concat scheme-program-name " -emacs"
 189           (if scheme-program-arguments
 190               (concat " " scheme-program-arguments)
 191               "")
 192           (if scheme-band-name
 193               (concat " -band " scheme-band-name)
 194               "")))
 195
 196 (defun reset-scheme ()
 197   "Reset the Scheme process."
 198   (interactive)
 199   (let ((process (get-process xscheme-process-name)))
 200     (cond ((or (not process)
 201                (not (eq (process-status process) 'run))
 202                (yes-or-no-p
 203 "The Scheme process is running, are you SURE you want to reset it? "))
 204            (message "Resetting Scheme process...")
 205            (if process
 206                (progn
 207                  (kill-process process t)
 208                  (delete-process process)))
 209            (xscheme-start-process xscheme-process-command-line
 210                                   xscheme-process-name
 211                                   xscheme-buffer-name)
 212            (message "Resetting Scheme process...done")))))
 213 \f
 214 ;;;; Multiple Scheme buffer management commands
 215
 216 (defun start-scheme (buffer-name &optional globally)
 217   "Choose a scheme interaction buffer, or create a new one."
 218   ;; (interactive "BScheme interaction buffer: \nP")
 219   (interactive
 220    (list (read-buffer "Scheme interaction buffer: "
 221                       xscheme-buffer-name
 222                       nil)
 223          current-prefix-arg))
 224   (let ((buffer (get-buffer-create buffer-name)))
 225     (let ((process (get-buffer-process buffer)))
 226       (if process
 227           (switch-to-buffer buffer)
 228         (if (or (not (buffer-file-name buffer))
 229                 (yes-or-no-p (concat "Buffer "
 230                                      (buffer-name buffer)
 231                                      " contains file "
 232                                      (buffer-file-name buffer)
 233                                      "; start scheme in it? ")))
 234             (progn
 235               (xscheme-start (xscheme-read-command-line t)
 236                              buffer-name
 237                              buffer-name)
 238               (if globally
 239                   (global-set-scheme-interaction-buffer buffer-name)))
 240           (message "start-scheme aborted"))))))
 241
 242 (fset 'select-scheme 'start-scheme)
 243
 244 (defun global-set-scheme-interaction-buffer (buffer-name)
 245   "Set the default scheme interaction buffer."
 246   (interactive
 247    (list (read-buffer "Scheme interaction buffer: "
 248                       xscheme-buffer-name
 249                       t)))
 250   (let ((process-name (verify-xscheme-buffer buffer-name nil)))
 251     (setq-default xscheme-buffer-name buffer-name)
 252     (setq-default xscheme-process-name process-name)
 253     (setq-default xscheme-runlight-string
 254                   (with-current-buffer buffer-name
 255                     xscheme-runlight-string))
 256     (setq-default xscheme-runlight
 257                   (if (eq (process-status process-name) 'run)
 258                       default-xscheme-runlight
 259                       ""))))
 260
 261 (defun local-set-scheme-interaction-buffer (buffer-name)
 262   "Set the scheme interaction buffer for the current buffer."
 263   (interactive
 264    (list (read-buffer "Scheme interaction buffer: "
 265                       xscheme-buffer-name
 266                       t)))
 267   (let ((process-name (verify-xscheme-buffer buffer-name t)))
 268     (set (make-local-variable 'xscheme-buffer-name) buffer-name)
 269     (set (make-local-variable 'xscheme-process-name) process-name)
 270     (set (make-local-variable 'xscheme-runlight)
 271          (with-current-buffer buffer-name
 272            xscheme-runlight))))
 273
 274 (defun local-clear-scheme-interaction-buffer ()
 275   "Make the current buffer use the default scheme interaction buffer."
 276   (interactive)
 277   (if (xscheme-process-buffer-current-p)
 278       (error "Cannot change the interaction buffer of an interaction buffer"))
 279   (kill-local-variable 'xscheme-buffer-name)
 280   (kill-local-variable 'xscheme-process-name)
 281   (kill-local-variable 'xscheme-runlight))
 282
 283 (defun verify-xscheme-buffer (buffer-name localp)
 284   (if (and localp (xscheme-process-buffer-current-p))
 285       (error "Cannot change the interaction buffer of an interaction buffer"))
 286   (let* ((buffer (get-buffer buffer-name))
 287          (process (and buffer (get-buffer-process buffer))))
 288     (cond ((not buffer)
 289            (error "Buffer `%s' does not exist" buffer-name))
 290           ((not process)
 291            (error "Buffer `%s' is not a scheme interaction buffer" buffer-name))
 292           (t
 293            (with-current-buffer buffer
 294              (if (not (xscheme-process-buffer-current-p))
 295                  (error "Buffer `%s' is not a scheme interaction buffer"
 296                         buffer-name)))
 297            (process-name process)))))
 298 \f
 299 ;;;; Interaction Mode
 300
 301 (defun scheme-interaction-mode (&optional preserve)
 302   "Major mode for interacting with an inferior MIT Scheme process.
 303 Like  scheme-mode  except that:
 304
 305 \\[xscheme-send-previous-expression] sends the expression before point to the Scheme process as input
 306 \\[xscheme-yank-pop] yanks an expression previously sent to Scheme
 307 \\[xscheme-yank-push] yanks an expression more recently sent to Scheme
 308
 309 All output from the Scheme process is written in the Scheme process
 310 buffer, which is initially named \"*scheme*\".  The result of
 311 evaluating a Scheme expression is also printed in the process buffer,
 312 preceded by the string \";Value: \" to highlight it.  If the process
 313 buffer is not visible at that time, the value will also be displayed
 314 in the minibuffer.  If an error occurs, the process buffer will
 315 automatically pop up to show you the error message.
 316
 317 While the Scheme process is running, the mode lines of all buffers in
 318 scheme-mode are modified to show the state of the process.  The
 319 possible states and their meanings are:
 320
 321 input           waiting for input
 322 run             evaluating
 323 gc              garbage collecting
 324
 325 The process buffer's mode line contains additional information where
 326 the buffer's name is normally displayed: the command interpreter level
 327 and type.
 328
 329 Scheme maintains a stack of command interpreters.  Every time an error
 330 or breakpoint occurs, the current command interpreter is pushed on the
 331 command interpreter stack, and a new command interpreter is started.
 332 One example of why this is done is so that an error that occurs while
 333 you are debugging another error will not destroy the state of the
 334 initial error, allowing you to return to it after the second error has
 335 been fixed.
 336
 337 The command interpreter level indicates how many interpreters are in
 338 the command interpreter stack.  It is initially set to one, and it is
 339 incremented every time that stack is pushed, and decremented every
 340 time it is popped.  The following commands are useful for manipulating
 341 the command interpreter stack:
 342
 343 \\[xscheme-send-breakpoint-interrupt]   pushes the stack once
 344 \\[xscheme-send-control-u-interrupt]    pops the stack once
 345 \\[xscheme-send-control-g-interrupt]    pops everything off
 346 \\[xscheme-send-control-x-interrupt]    aborts evaluation, doesn't affect stack
 347
 348 Some possible command interpreter types and their meanings are:
 349
 350 [Evaluator]     read-eval-print loop for evaluating expressions
 351 [Debugger]      single character commands for debugging errors
 352 [Where]         single character commands for examining environments
 353
 354 Starting with release 6.2 of Scheme, the latter two types of command
 355 interpreters will change the major mode of the Scheme process buffer
 356 to scheme-debugger-mode , in which the evaluation commands are
 357 disabled, and the keys which normally self insert instead send
 358 themselves to the Scheme process.  The command character ? will list
 359 the available commands.
 360
 361 For older releases of Scheme, the major mode will be be
 362 scheme-interaction-mode , and the command characters must be sent as
 363 if they were expressions.
 364
 365 Commands:
 366 Delete converts tabs to spaces as it moves back.
 367 Blank lines separate paragraphs.  Semicolons start comments.
 368 \\{scheme-interaction-mode-map}
 369
 370 Entry to this mode calls the value of scheme-interaction-mode-hook
 371 with no args, if that value is non-nil.
 372  Likewise with the value of scheme-mode-hook.
 373  scheme-interaction-mode-hook is called after scheme-mode-hook."
 374   ;; FIXME: Use define-derived-mode.
 375   (interactive "P")
 376   (if (not preserve)
 377       (let ((previous-mode major-mode))
 378         (kill-all-local-variables)
 379         (make-local-variable 'xscheme-runlight-string)
 380         (make-local-variable 'xscheme-runlight)
 381         (set (make-local-variable 'xscheme-previous-mode) previous-mode)
 382         (let ((buffer (current-buffer)))
 383           (set (make-local-variable 'xscheme-buffer-name) (buffer-name buffer))
 384           (set (make-local-variable 'xscheme-last-input-end) (make-marker))
 385           (let ((process (get-buffer-process buffer)))
 386             (when process
 387               (setq-local xscheme-process-name (process-name process))
 388               ;; FIXME: Use add-function!
 389               (xscheme-process-filter-initialize t)
 390               (xscheme-mode-line-initialize xscheme-buffer-name)
 391               (add-function :override (process-sentinel process)
 392                             #'xscheme-process-sentinel)
 393               (add-function :override (process-filter process)
 394                             #'xscheme-process-filter))))))
 395   (scheme-interaction-mode-initialize)
 396   (scheme-mode-variables)
 397   (run-mode-hooks 'scheme-mode-hook 'scheme-interaction-mode-hook))
 398
 399 (defun exit-scheme-interaction-mode ()
 400   "Take buffer out of scheme interaction mode."
 401   (interactive)
 402   (if (not (derived-mode-p 'scheme-interaction-mode))
 403       (error "Buffer not in scheme interaction mode"))
 404   (funcall xscheme-previous-mode)
 405   (let ((process (get-buffer-process (current-buffer))))
 406     (when process
 407       (remove-function (process-sentinel process) #'xscheme-process-sentinel)
 408       (remove-function (process-filter process) #'xscheme-process-filter))))
 409
 410 (defvar scheme-interaction-mode-commands-alist nil)
 411 (defvar scheme-interaction-mode-map nil)
 412
 413 (defun scheme-interaction-mode-initialize ()
 414   (use-local-map scheme-interaction-mode-map)
 415   (setq major-mode 'scheme-interaction-mode) ;FIXME: Use define-derived-mode.
 416   (setq mode-name "Scheme Interaction"))
 417
 418 (defun scheme-interaction-mode-commands (keymap)
 419   (let ((entries scheme-interaction-mode-commands-alist))
 420     (while entries
 421       (define-key keymap
 422         (car (car entries))
 423         (car (cdr (car entries))))
 424       (setq entries (cdr entries)))))
 425
 426 ;; Initialize the command alist
 427 (setq scheme-interaction-mode-commands-alist
 428       (append scheme-interaction-mode-commands-alist
 429               '(("\C-c\C-m" xscheme-send-current-line)
 430                 ("\C-c\C-o" xscheme-delete-output)
 431                 ("\C-c\C-p" xscheme-send-proceed)
 432                 ("\C-c\C-y" xscheme-yank)
 433                 ("\ep" xscheme-yank-pop)
 434                 ("\en" xscheme-yank-push))))
 435
 436 ;; Initialize the mode map
 437 (if (not scheme-interaction-mode-map)
 438     (progn
 439       (setq scheme-interaction-mode-map (make-keymap))
 440       (scheme-mode-commands scheme-interaction-mode-map)
 441       (xscheme-interrupt-commands scheme-interaction-mode-map)
 442       (xscheme-evaluation-commands scheme-interaction-mode-map)
 443       (scheme-interaction-mode-commands scheme-interaction-mode-map)))
 444
 445 (defun xscheme-enter-interaction-mode ()
 446   (with-current-buffer (xscheme-process-buffer)
 447     (if (not (derived-mode-p 'scheme-interaction-mode))
 448         (if (derived-mode-p 'scheme-debugger-mode)
 449             (scheme-interaction-mode-initialize)
 450             (scheme-interaction-mode t)))))
 451
 452 (define-obsolete-function-alias 'advertised-xscheme-send-previous-expression
 453   'xscheme-send-previous-expression "23.2")
 454 \f
 455 ;;;; Debugger Mode
 456
 457 (defun scheme-debugger-mode ()
 458   "Major mode for executing the Scheme debugger.
 459 Like  scheme-mode  except that the evaluation commands
 460 are disabled, and characters that would normally be self inserting are
 461 sent to the Scheme process instead.  Typing ?  will show you which
 462 characters perform useful functions.
 463
 464 Commands:
 465 \\{scheme-debugger-mode-map}"
 466   (error "Invalid entry to scheme-debugger-mode"))
 467
 468 (defvar scheme-debugger-mode-map nil)
 469
 470 (defun scheme-debugger-mode-initialize ()
 471   (use-local-map scheme-debugger-mode-map)
 472   (setq major-mode 'scheme-debugger-mode) ;FIXME: Use define-derived-mode.
 473   (setq mode-name "Scheme Debugger"))
 474
 475 (defun scheme-debugger-mode-commands (keymap)
 476   (let ((char ?\s))
 477     (while (< char 127)
 478       (define-key keymap (char-to-string char) 'scheme-debugger-self-insert)
 479       (setq char (1+ char)))))
 480
 481 ;; Initialize the debugger mode map
 482 (if (not scheme-debugger-mode-map)
 483     (progn
 484       (setq scheme-debugger-mode-map (make-keymap))
 485       (scheme-mode-commands scheme-debugger-mode-map)
 486       (xscheme-interrupt-commands scheme-debugger-mode-map)
 487       (scheme-debugger-mode-commands scheme-debugger-mode-map)))
 488
 489 (defun scheme-debugger-self-insert ()
 490   "Transmit this character to the Scheme process."
 491   (interactive)
 492   (xscheme-send-char last-command-event))
 493
 494 (defun xscheme-enter-debugger-mode (_prompt-string)
 495   (with-current-buffer (xscheme-process-buffer)
 496     (if (not (derived-mode-p 'scheme-debugger-mode))
 497         (progn
 498           (if (not (derived-mode-p 'scheme-interaction-mode))
 499               (scheme-interaction-mode t))
 500           (scheme-debugger-mode-initialize)))))
 501
 502 (defun xscheme-debugger-mode-p ()
 503   (let ((buffer (xscheme-process-buffer)))
 504     (and buffer
 505          (with-current-buffer buffer
 506            (derived-mode-p 'scheme-debugger-mode)))))
 507 \f
 508 ;;;; Evaluation Commands
 509
 510 (defun xscheme-send-string (&rest strings)
 511   "Send the string arguments to the Scheme process.
 512 The strings are concatenated and terminated by a newline."
 513   (cond ((not (xscheme-process-running-p))
 514          (if (yes-or-no-p "The Scheme process has died.  Reset it? ")
 515              (progn
 516                (reset-scheme)
 517                (xscheme-wait-for-process)
 518                (xscheme-send-string-1 strings))))
 519         ((xscheme-debugger-mode-p) (error "No sends allowed in debugger mode"))
 520         ((and (not xscheme-allow-pipelined-evaluation)
 521               xscheme-running-p)
 522          (error "No sends allowed while Scheme running"))
 523         (t (xscheme-send-string-1 strings))))
 524
 525 (defun xscheme-send-string-1 (strings)
 526   (let ((string (apply 'concat strings)))
 527     (xscheme-send-string-2 string)
 528     (if (derived-mode-p 'scheme-interaction-mode)
 529         (xscheme-insert-expression string))))
 530
 531 (defun xscheme-send-string-2 (string)
 532   (let ((process (get-process xscheme-process-name)))
 533     (process-send-string process (concat string "\n"))
 534     (if (xscheme-process-buffer-current-p)
 535         (set-marker (process-mark process) (point)))))
 536
 537 (defun xscheme-select-process-buffer ()
 538   "Select the Scheme process buffer and move to its output point."
 539   (interactive)
 540   (let ((process
 541          (or (get-process xscheme-process-name)
 542              (error "No scheme process"))))
 543     (let ((buffer (or (process-buffer process) (error "No process buffer"))))
 544       (let ((window (get-buffer-window buffer)))
 545         (if window
 546             (select-window window)
 547             (switch-to-buffer buffer))
 548         (goto-char (process-mark process))))))
 549 \f
 550 ;;;; Scheme expressions ring
 551
 552 (defun xscheme-insert-expression (string)
 553   (setq xscheme-expressions-ring-yank-pointer
 554         (add-to-history 'xscheme-expressions-ring string
 555                         xscheme-expressions-ring-max)))
 556
 557 (defun xscheme-rotate-yank-pointer (arg)
 558   "Rotate the yanking point in the kill ring."
 559   (interactive "p")
 560   (let ((length (length xscheme-expressions-ring)))
 561     (if (zerop length)
 562         (error "Scheme expression ring is empty")
 563         (setq xscheme-expressions-ring-yank-pointer
 564               (let ((index
 565                      (% (+ arg
 566                            (- length
 567                               (length xscheme-expressions-ring-yank-pointer)))
 568                         length)))
 569                 (nthcdr (if (< index 0)
 570                             (+ index length)
 571                             index)
 572                         xscheme-expressions-ring))))))
 573
 574 (defun xscheme-yank (&optional arg)
 575   "Insert the most recent expression at point.
 576 With just C-U as argument, same but put point in front (and mark at end).
 577 With argument n, reinsert the nth most recently sent expression.
 578 See also the commands \\[xscheme-yank-pop] and \\[xscheme-yank-push]."
 579   (interactive "*P")
 580   (xscheme-rotate-yank-pointer (if (listp arg) 0
 581                                  (if (eq arg '-) -1
 582                                    (1- arg))))
 583   (push-mark (point))
 584   (insert (car xscheme-expressions-ring-yank-pointer))
 585   (if (consp arg)
 586       (exchange-point-and-mark)))
 587
 588 ;; Old name, to avoid errors in users' init files.
 589 (fset 'xscheme-yank-previous-send
 590       'xscheme-yank)
 591
 592 (defun xscheme-yank-pop (arg)
 593   "Insert or replace a just-yanked expression with an older expression.
 594 If the previous command was not a yank, it yanks.
 595 Otherwise, the region contains a stretch of reinserted
 596 expression.  yank-pop deletes that text and inserts in its
 597 place a different expression.
 598
 599 With no argument, the next older expression is inserted.
 600 With argument n, the n'th older expression is inserted.
 601 If n is negative, this is a more recent expression.
 602
 603 The sequence of expressions wraps around, so that after the oldest one
 604 comes the newest one."
 605   (interactive "*p")
 606   (setq this-command 'xscheme-yank)
 607   (if (not (eq last-command 'xscheme-yank))
 608       (progn
 609         (xscheme-yank)
 610         (setq arg (- arg 1))))
 611   (if (not (= arg 0))
 612       (let ((before (< (point) (mark))))
 613         (delete-region (point) (mark))
 614         (xscheme-rotate-yank-pointer arg)
 615         (set-mark (point))
 616         (insert (car xscheme-expressions-ring-yank-pointer))
 617         (if before (exchange-point-and-mark)))))
 618
 619 (defun xscheme-yank-push (arg)
 620   "Insert or replace a just-yanked expression with a more recent expression.
 621 If the previous command was not a yank, it yanks.
 622 Otherwise, the region contains a stretch of reinserted
 623 expression.  yank-pop deletes that text and inserts in its
 624 place a different expression.
 625
 626 With no argument, the next more recent expression is inserted.
 627 With argument n, the n'th more recent expression is inserted.
 628 If n is negative, a less recent expression is used.
 629
 630 The sequence of expressions wraps around, so that after the oldest one
 631 comes the newest one."
 632   (interactive "*p")
 633   (xscheme-yank-pop (- 0 arg)))
 634 \f
 635 (defun xscheme-send-region (start end)
 636   "Send the current region to the Scheme process.
 637 The region is sent terminated by a newline."
 638   (interactive "r")
 639   (if (xscheme-process-buffer-current-p)
 640       (progn
 641         (goto-char end)
 642         (if (not (bolp))
 643             (insert-before-markers ?\n))
 644         (set-marker (process-mark (get-process xscheme-process-name))
 645                     (point))
 646         (set-marker xscheme-last-input-end (point))))
 647   (xscheme-send-string (buffer-substring start end)))
 648
 649 (defun xscheme-send-definition ()
 650   "Send the current definition to the Scheme process.
 651 If the current line begins with a non-whitespace character,
 652 parse an expression from the beginning of the line and send that instead."
 653   (interactive)
 654   (let ((start nil) (end nil))
 655     (save-excursion
 656       (end-of-defun)
 657       (setq end (point))
 658       (if (re-search-backward "^\\s(" nil t)
 659           (setq start (point))
 660           (error "Can't find definition")))
 661     (xscheme-send-region start end)))
 662
 663 (defun xscheme-send-next-expression ()
 664   "Send the expression to the right of `point' to the Scheme process."
 665   (interactive)
 666   (let ((start (point)))
 667     (xscheme-send-region start (save-excursion (forward-sexp) (point)))))
 668
 669 (defun xscheme-send-previous-expression ()
 670   "Send the expression to the left of `point' to the Scheme process."
 671   (interactive)
 672   (let ((end (point)))
 673     (xscheme-send-region (save-excursion (backward-sexp) (point)) end)))
 674 \f
 675 (defun xscheme-send-current-line ()
 676   "Send the current line to the Scheme process.
 677 Useful for working with debugging Scheme under adb."
 678   (interactive)
 679   (let ((line (buffer-substring (line-beginning-position) (line-end-position))))
 680     (end-of-line)
 681     (insert ?\n)
 682     (xscheme-send-string-2 line)))
 683
 684 (defun xscheme-send-buffer ()
 685   "Send the current buffer to the Scheme process."
 686   (interactive)
 687   (if (xscheme-process-buffer-current-p)
 688       (error "Not allowed to send this buffer's contents to Scheme"))
 689   (xscheme-send-region (point-min) (point-max)))
 690
 691 (defun xscheme-send-char (char)
 692   "Prompt for a character and send it to the Scheme process."
 693   (interactive "cCharacter to send: ")
 694   (process-send-string xscheme-process-name (char-to-string char)))
 695
 696 (defun xscheme-delete-output ()
 697   "Delete all output from interpreter since last input."
 698   (interactive)
 699   (let ((proc (get-buffer-process (current-buffer))))
 700     (save-excursion
 701       (goto-char (process-mark proc))
 702       (re-search-backward
 703        "^;\\(Unspecified return value$\\|Value\\( [0-9]+\\)?: \\|\\(Abort\\|Up\\|Quit\\)!$\\)"
 704        xscheme-last-input-end
 705        t)
 706       (forward-line 0)
 707       (if (< (marker-position xscheme-last-input-end) (point))
 708           (progn
 709             (delete-region xscheme-last-input-end (point))
 710             (insert-before-markers "*** output flushed ***\n"))))))
 711 \f
 712 ;;;; Interrupts
 713
 714 (defun xscheme-send-breakpoint-interrupt ()
 715   "Cause the Scheme process to enter a breakpoint."
 716   (interactive)
 717   (xscheme-send-interrupt ?b nil))
 718
 719 (defun xscheme-send-proceed ()
 720   "Cause the Scheme process to proceed from a breakpoint."
 721   (interactive)
 722   (process-send-string xscheme-process-name "(proceed)\n"))
 723
 724 (defconst xscheme-control-g-message-string
 725   "Sending C-G interrupt to Scheme...")
 726
 727 (defun xscheme-send-control-g-interrupt ()
 728   "Cause the Scheme processor to halt and flush input.
 729 Control returns to the top level rep loop."
 730   (interactive)
 731   (let ((inhibit-quit t))
 732     (cond ((not xscheme-control-g-synchronization-p)
 733            (interrupt-process xscheme-process-name))
 734           ((with-current-buffer xscheme-buffer-name
 735              xscheme-control-g-disabled-p)
 736            (message "Relax..."))
 737           (t
 738            (with-current-buffer xscheme-buffer-name
 739              (setq xscheme-control-g-disabled-p t))
 740            (message xscheme-control-g-message-string)
 741            (interrupt-process xscheme-process-name)
 742            (sleep-for 0.1)
 743            (xscheme-send-char 0)))))
 744
 745 (defun xscheme-send-control-u-interrupt ()
 746   "Cause the Scheme process to halt, returning to previous rep loop."
 747   (interactive)
 748   (xscheme-send-interrupt ?u t))
 749
 750 (defun xscheme-send-control-x-interrupt ()
 751   "Cause the Scheme process to halt, returning to current rep loop."
 752   (interactive)
 753   (xscheme-send-interrupt ?x t))
 754
 755 ;;; This doesn't really work right -- Scheme just gobbles the first
 756 ;;; character in the input.  There is no way for us to guarantee that
 757 ;;; the argument to this procedure is the first char unless we put
 758 ;;; some kind of marker in the input stream.
 759
 760 (defun xscheme-send-interrupt (char mark-p)
 761   "Send a ^A type interrupt to the Scheme process."
 762   (interactive "cInterrupt character to send: ")
 763   (quit-process xscheme-process-name)
 764   (sleep-for 0.1)
 765   (xscheme-send-char char)
 766   (if (and mark-p xscheme-control-g-synchronization-p)
 767       (xscheme-send-char 0)))
 768 \f
 769 ;;;; Basic Process Control
 770
 771 (defun xscheme-start-process (command-line the-process the-buffer)
 772   (let ((buffer (get-buffer-create the-buffer)))
 773     (let ((process (get-buffer-process buffer)))
 774       (with-current-buffer buffer
 775         (if (and process (memq (process-status process) '(run stop)))
 776             (set-marker (process-mark process) (point-max))
 777             (progn (if process (delete-process process))
 778                    (goto-char (point-max))
 779                    (scheme-interaction-mode nil)
 780                    (setq xscheme-process-name the-process)
 781                    (if (bobp)
 782                        (insert-before-markers
 783                         (substitute-command-keys xscheme-startup-message)))
 784                    (setq process
 785                          (let ((process-connection-type nil))
 786                            (apply 'start-process
 787                                   (cons the-process
 788                                         (cons buffer
 789                                               (xscheme-parse-command-line
 790                                                command-line))))))
 791                    (if (not (equal (process-name process) the-process))
 792                        (setq xscheme-process-name (process-name process)))
 793                    (if (not (equal (buffer-name buffer) the-buffer))
 794                        (setq xscheme-buffer-name (buffer-name buffer)))
 795                    (message "Starting process %s in buffer %s"
 796                             xscheme-process-name
 797                             xscheme-buffer-name)
 798                    (set-marker (process-mark process) (point-max))
 799                    (xscheme-process-filter-initialize t)
 800                    (xscheme-mode-line-initialize xscheme-buffer-name)
 801                    (set-process-sentinel process 'xscheme-process-sentinel)
 802                    (set-process-filter process 'xscheme-process-filter)
 803                    (run-hooks 'xscheme-start-hook)))))
 804     buffer))
 805
 806 (defun xscheme-parse-command-line (string)
 807   (setq string (substitute-in-file-name string))
 808   (let ((start 0)
 809         (result '()))
 810     (while start
 811       (let ((index (string-match "[ \t]" string start)))
 812         (setq start
 813               (cond ((not index)
 814                      (setq result
 815                            (cons (substring string start)
 816                                  result))
 817                      nil)
 818                     ((= index start)
 819                      (string-match "[^ \t]" string start))
 820                     (t
 821                      (setq result
 822                            (cons (substring string start index)
 823                                  result))
 824                      (1+ index))))))
 825     (nreverse result)))
 826 \f
 827 (defun xscheme-wait-for-process ()
 828   (sleep-for 2)
 829   (while xscheme-running-p
 830     (sleep-for 1)))
 831
 832 (defun xscheme-process-running-p ()
 833   "True if there is a Scheme process whose status is `run'."
 834   (let ((process (get-process xscheme-process-name)))
 835     (and process
 836          (eq (process-status process) 'run))))
 837
 838 (defun xscheme-process-buffer ()
 839   (let ((process (get-process xscheme-process-name)))
 840     (and process (process-buffer process))))
 841
 842 (defun xscheme-process-buffer-window ()
 843   (let ((buffer (xscheme-process-buffer)))
 844     (and buffer (get-buffer-window buffer))))
 845
 846 (defun xscheme-process-buffer-current-p ()
 847   "True if the current buffer is the Scheme process buffer."
 848   (eq (xscheme-process-buffer) (current-buffer)))
 849 \f
 850 ;;;; Process Filter Operations
 851
 852 (defvar xscheme-process-filter-alist
 853   '((?A xscheme-eval
 854         xscheme-process-filter:string-action-noexcursion)
 855     (?D xscheme-enter-debugger-mode
 856         xscheme-process-filter:string-action)
 857     (?E xscheme-eval
 858         xscheme-process-filter:string-action)
 859     (?P xscheme-set-prompt-variable
 860         xscheme-process-filter:string-action)
 861     (?R xscheme-enter-interaction-mode
 862         xscheme-process-filter:simple-action)
 863     (?b xscheme-start-gc
 864         xscheme-process-filter:simple-action)
 865     (?c xscheme-unsolicited-read-char
 866         xscheme-process-filter:simple-action)
 867     (?e xscheme-finish-gc
 868         xscheme-process-filter:simple-action)
 869     (?f xscheme-exit-input-wait
 870         xscheme-process-filter:simple-action)
 871     (?g xscheme-enable-control-g
 872         xscheme-process-filter:simple-action)
 873     (?i xscheme-prompt-for-expression
 874         xscheme-process-filter:string-action)
 875     (?m xscheme-message
 876         xscheme-process-filter:string-action)
 877     (?n xscheme-prompt-for-confirmation
 878         xscheme-process-filter:string-action)
 879     (?o xscheme-output-goto
 880         xscheme-process-filter:simple-action)
 881     (?p xscheme-set-prompt
 882         xscheme-process-filter:string-action)
 883     (?s xscheme-enter-input-wait
 884         xscheme-process-filter:simple-action)
 885     (?v xscheme-write-value
 886         xscheme-process-filter:string-action)
 887     (?w xscheme-cd
 888         xscheme-process-filter:string-action)
 889     (?z xscheme-display-process-buffer
 890         xscheme-process-filter:simple-action))
 891   "Table used to decide how to handle process filter commands.
 892 Value is a list of entries, each entry is a list of three items.
 893
 894 The first item is the character that the process filter dispatches on.
 895 The second item is the action to be taken, a function.
 896 The third item is the handler for the entry, a function.
 897
 898 When the process filter sees a command whose character matches a
 899 particular entry, it calls the handler with two arguments: the action
 900 and the string containing the rest of the process filter's input
 901 stream.  It is the responsibility of the handler to invoke the action
 902 with the appropriate arguments, and to reenter the process filter with
 903 the remaining input.")
 904 \f
 905 ;;;; Process Filter
 906
 907 (defun xscheme-process-sentinel (proc reason)
 908   (let* ((buffer (process-buffer proc))
 909          (name (buffer-name buffer)))
 910     (with-current-buffer buffer
 911       (xscheme-process-filter-initialize (eq reason 'run))
 912       (if (not (eq reason 'run))
 913           (progn
 914             (setq scheme-mode-line-process "")
 915             (setq xscheme-mode-string "no process")
 916             (if (equal name (default-value 'xscheme-buffer-name))
 917                 (setq-default xscheme-runlight ""))))
 918       (if (and (not (memq reason '(run stop)))
 919                xscheme-signal-death-message)
 920           (progn
 921             (beep)
 922             (message
 923 "The Scheme process has died!  Do M-x reset-scheme to restart it"))))))
 924
 925 (defun xscheme-process-filter-initialize (running-p)
 926   (setq xscheme-process-filter-state 'idle)
 927   (setq xscheme-running-p running-p)
 928   (setq xscheme-control-g-disabled-p nil)
 929   (setq xscheme-allow-output-p t)
 930   (setq xscheme-prompt "")
 931   (if running-p
 932       (let ((name (buffer-name (current-buffer))))
 933         (setq scheme-mode-line-process '(": " xscheme-runlight-string))
 934         (xscheme-mode-line-initialize name)
 935         (if (equal name (default-value 'xscheme-buffer-name))
 936             (setq-default xscheme-runlight default-xscheme-runlight))))
 937   (if (or (eq xscheme-runlight default-xscheme-runlight)
 938           (equal xscheme-runlight ""))
 939       (setq xscheme-runlight (list ": " 'xscheme-buffer-name ": " "?")))
 940   (rplaca (nthcdr 3 xscheme-runlight)
 941           (if running-p "?" "no process")))
 942
 943 (defun xscheme-process-filter (proc string)
 944   (let ((xscheme-filter-input string)
 945         (call-noexcursion nil))
 946     (while xscheme-filter-input
 947       (setq call-noexcursion nil)
 948       (with-current-buffer (process-buffer proc)
 949         (cond ((eq xscheme-process-filter-state 'idle)
 950                (let ((start (string-match "\e" xscheme-filter-input)))
 951                  (if start
 952                      (progn
 953                        (xscheme-process-filter-output
 954                         (substring xscheme-filter-input 0 start))
 955                        (setq xscheme-filter-input
 956                              (substring xscheme-filter-input (1+ start)))
 957                        (setq xscheme-process-filter-state 'reading-type))
 958                    (let ((string xscheme-filter-input))
 959                      (setq xscheme-filter-input nil)
 960                      (xscheme-process-filter-output string)))))
 961               ((eq xscheme-process-filter-state 'reading-type)
 962                (if (zerop (length xscheme-filter-input))
 963                    (setq xscheme-filter-input nil)
 964                  (let ((char (aref xscheme-filter-input 0)))
 965                    (setq xscheme-filter-input
 966                          (substring xscheme-filter-input 1))
 967                    (let ((entry (assoc char xscheme-process-filter-alist)))
 968                      (if entry
 969                          (funcall (nth 2 entry) (nth 1 entry))
 970                        (progn
 971                          (xscheme-process-filter-output ?\e char)
 972                          (setq xscheme-process-filter-state 'idle)))))))
 973               ((eq xscheme-process-filter-state 'reading-string)
 974                (let ((start (string-match "\e" xscheme-filter-input)))
 975                  (if start
 976                      (let ((string
 977                             (concat xscheme-string-accumulator
 978                                     (substring xscheme-filter-input 0 start))))
 979                        (setq xscheme-filter-input
 980                              (substring xscheme-filter-input (1+ start)))
 981                        (setq xscheme-process-filter-state 'idle)
 982                        (if (listp xscheme-string-receiver)
 983                            (progn
 984                              (setq xscheme-string-receiver
 985                                    (car xscheme-string-receiver))
 986                              (setq call-noexcursion string))
 987                          (funcall xscheme-string-receiver string)))
 988                    (progn
 989                      (setq xscheme-string-accumulator
 990                            (concat xscheme-string-accumulator
 991                                    xscheme-filter-input))
 992                      (setq xscheme-filter-input nil)))))
 993               (t
 994                (error "Scheme process filter -- bad state"))))
 995       (if call-noexcursion
 996           (funcall xscheme-string-receiver call-noexcursion)))))
 997 \f
 998 ;;;; Process Filter Output
 999
1000 (defun xscheme-process-filter-output (&rest args)
1001   (if xscheme-allow-output-p
1002       (let ((string (apply 'concat args)))
1003         (save-excursion
1004           (xscheme-goto-output-point)
1005           (let ((old-point (point)))
1006             (while (string-match "\\(\007\\|\f\\)" string)
1007               (let ((start (match-beginning 0)))
1008                 (insert-before-markers (substring string 0 start))
1009                 (if (= ?\f (aref string start))
1010                     (progn
1011                       (if (not (bolp))
1012                           (insert-before-markers ?\n))
1013                       (insert-before-markers ?\f))
1014                     (beep))
1015                 (setq string (substring string (1+ start)))))
1016             (insert-before-markers string)
1017             (if (and xscheme-last-input-end
1018                      (equal (marker-position xscheme-last-input-end) (point)))
1019                 (set-marker xscheme-last-input-end old-point)))))))
1020
1021 (defun xscheme-guarantee-newlines (n)
1022   (if xscheme-allow-output-p
1023       (save-excursion
1024         (xscheme-goto-output-point)
1025         (let ((stop nil))
1026           (while (and (not stop)
1027                       (bolp))
1028             (setq n (1- n))
1029             (if (bobp)
1030                 (setq stop t)
1031                 (backward-char))))
1032         (xscheme-goto-output-point)
1033         (while (> n 0)
1034           (insert-before-markers ?\n)
1035           (setq n (1- n))))))
1036
1037 (defun xscheme-goto-output-point ()
1038   (let ((process (get-process xscheme-process-name)))
1039     (set-buffer (process-buffer process))
1040     (goto-char (process-mark process))))
1041
1042 (defun xscheme-mode-line-initialize (name)
1043   (setq xscheme-runlight-string "")
1044   (if (equal name (default-value 'xscheme-buffer-name))
1045       (setq-default xscheme-runlight-string ""))
1046   (setq xscheme-mode-string "")
1047   (setq mode-line-buffer-identification
1048         (list (concat name ": ")
1049               'xscheme-mode-string)))
1050
1051 (defun xscheme-set-runlight (runlight)
1052   (setq xscheme-runlight-string runlight)
1053   (if (equal (buffer-name (current-buffer))
1054              (default-value 'xscheme-buffer-name))
1055       (setq-default xscheme-runlight-string runlight))
1056   (rplaca (nthcdr 3 xscheme-runlight) runlight)
1057   (force-mode-line-update t))
1058 \f
1059 (defun xscheme-process-filter:simple-action (action)
1060   (setq xscheme-process-filter-state 'idle)
1061   (funcall action))
1062
1063 (defun xscheme-process-filter:string-action (action)
1064   (setq xscheme-string-receiver action)
1065   (setq xscheme-string-accumulator "")
1066   (setq xscheme-process-filter-state 'reading-string))
1067
1068 (defun xscheme-process-filter:string-action-noexcursion (action)
1069   (xscheme-process-filter:string-action (cons action nil)))
1070
1071 (defconst xscheme-runlight:running "run"
1072   "The character displayed when the Scheme process is running.")
1073
1074 (defconst xscheme-runlight:input "input"
1075   "The character displayed when the Scheme process is waiting for input.")
1076
1077 (defconst xscheme-runlight:gc "gc"
1078   "The character displayed when the Scheme process is garbage collecting.")
1079
1080 (defun xscheme-start-gc ()
1081   (xscheme-set-runlight xscheme-runlight:gc))
1082
1083 (defun xscheme-finish-gc ()
1084   (xscheme-set-runlight
1085    (if xscheme-running-p xscheme-runlight:running xscheme-runlight:input)))
1086
1087 (defun xscheme-enter-input-wait ()
1088   (xscheme-set-runlight xscheme-runlight:input)
1089   (setq xscheme-control-g-disabled-p nil)
1090   (setq xscheme-running-p nil))
1091
1092 (defun xscheme-exit-input-wait ()
1093   (xscheme-set-runlight xscheme-runlight:running)
1094   (setq xscheme-running-p t))
1095
1096 (defun xscheme-enable-control-g ()
1097   (setq xscheme-control-g-disabled-p nil)
1098   (if (string= (current-message) xscheme-control-g-message-string)
1099       (message nil)))
1100
1101 (defun xscheme-display-process-buffer ()
1102   (let ((window (or (xscheme-process-buffer-window)
1103                     (display-buffer (xscheme-process-buffer)))))
1104     (save-window-excursion
1105       (select-window window)
1106       (xscheme-goto-output-point)
1107       (if (xscheme-debugger-mode-p)
1108           (xscheme-enter-interaction-mode)))))
1109
1110 (defun xscheme-unsolicited-read-char ()
1111   nil)
1112 \f
1113 (defun xscheme-eval (string)
1114   (eval (car (read-from-string string))))
1115
1116 (defun xscheme-message (string)
1117   (if (not (zerop (length string)))
1118       (xscheme-write-message-1 string (format ";%s" string))))
1119
1120 (defun xscheme-write-value (string)
1121   (if (zerop (length string))
1122       (xscheme-write-message-1 "(no value)" ";Unspecified return value")
1123       (xscheme-write-message-1 string (format ";Value: %s" string))))
1124
1125 (defun xscheme-write-message-1 (message-string output-string)
1126   (let* ((process (get-process xscheme-process-name))
1127          (window (get-buffer-window (process-buffer process))))
1128     (if (or (not window)
1129             (not (pos-visible-in-window-p (process-mark process)
1130                                           window)))
1131         (message "%s" message-string)))
1132   (xscheme-guarantee-newlines 1)
1133   (xscheme-process-filter-output output-string))
1134
1135 (defun xscheme-set-prompt-variable (string)
1136   (setq xscheme-prompt string))
1137
1138 (defun xscheme-set-prompt (string)
1139   (setq xscheme-prompt string)
1140   (xscheme-guarantee-newlines 2)
1141   (setq xscheme-mode-string (xscheme-coerce-prompt string))
1142   (force-mode-line-update t))
1143
1144 (defun xscheme-output-goto ()
1145   (xscheme-goto-output-point)
1146   (xscheme-guarantee-newlines 2))
1147
1148 (defun xscheme-coerce-prompt (string)
1149   (if (string-match "^[0-9]+ \\[[^]]+\\] " string)
1150       (let ((end (match-end 0)))
1151         (xscheme-process-filter-output (substring string end))
1152         (substring string 0 (- end 1)))
1153       string))
1154
1155 (defun xscheme-cd (directory-string)
1156   (with-current-buffer (xscheme-process-buffer)
1157     (cd directory-string)))
1158 \f
1159 (defun xscheme-prompt-for-confirmation (prompt-string)
1160   (xscheme-send-char (if (y-or-n-p prompt-string) ?y ?n)))
1161
1162 (defvar xscheme-prompt-for-expression-map nil)
1163 (if (not xscheme-prompt-for-expression-map)
1164     (progn
1165       (setq xscheme-prompt-for-expression-map
1166             (copy-keymap minibuffer-local-map))
1167       (substitute-key-definition 'exit-minibuffer
1168                                  'xscheme-prompt-for-expression-exit
1169                                  xscheme-prompt-for-expression-map)))
1170
1171 (defun xscheme-prompt-for-expression (prompt-string)
1172   (xscheme-send-string-2
1173    (read-from-minibuffer prompt-string nil xscheme-prompt-for-expression-map)))
1174
1175 (defun xscheme-prompt-for-expression-exit ()
1176   (interactive)
1177   (if (eq (xscheme-region-expression-p (minibuffer-prompt-end) (point-max))
1178           'one)
1179       (exit-minibuffer)
1180     (error "Input must be a single, complete expression")))
1181
1182 (defun xscheme-region-expression-p (start end)
1183   (save-excursion
1184     (let ((old-syntax-table (syntax-table)))
1185       (unwind-protect
1186           (progn
1187             (set-syntax-table scheme-mode-syntax-table)
1188             (let ((state (parse-partial-sexp start end)))
1189               (and (zerop (car state))  ;depth = 0
1190                    (nth 2 state)        ;last-sexp exists, i.e. >= 1 sexps
1191                    (let ((state (parse-partial-sexp start (nth 2 state))))
1192                      (if (nth 2 state) 'many 'one)))))
1193         (set-syntax-table old-syntax-table)))))
1194
1195 (provide 'xscheme)
1196
1197 ;;; xscheme.el ends here