0.pre8.81:

[sbcl/lichteblau.git] / src / code / toplevel.lisp

;;;; stuff related to the toplevel read-eval-print loop, plus some
;;;; other miscellaneous functions that we don't have any better place
;;;; for

;;;; This software is part of the SBCL system. See the README file for
;;;; more information.
;;;;
;;;; This software is derived from the CMU CL system, which was
;;;; written at Carnegie Mellon University and released into the
;;;; public domain. The software is in the public domain and is
;;;; provided with absolutely no warranty. See the COPYING and CREDITS
;;;; files for more information.

(in-package "SB!IMPL")
\f
;;;; magic specials initialized by GENESIS

;;; FIXME: The DEFVAR here is redundant with the (DECLAIM (SPECIAL ..))
;;; of all static symbols in early-impl.lisp.
(progn
  (defvar *current-catch-block*)
  (defvar *current-unwind-protect-block*)
  (defvar *free-interrupt-context-index*))
\f
;;; specials initialized by !COLD-INIT

;;; FIXME: These could be converted to DEFVARs.
(declaim (special *gc-inhibit* *already-maybe-gcing*
                  *need-to-collect-garbage*
                  *gc-notify-stream*
                  *before-gc-hooks* *after-gc-hooks*
                  #!+x86 *pseudo-atomic-atomic*
                  #!+x86 *pseudo-atomic-interrupted*
                  sb!unix::*interrupts-enabled*
                  sb!unix::*interrupt-pending*
                  *type-system-initialized*))

(defvar *cold-init-complete-p*)

;;; counts of nested errors (with internal errors double-counted)
(defvar *maximum-error-depth*)
(defvar *current-error-depth*)
\f
;;;; miscellaneous utilities for working with with TOPLEVEL

;;; Execute BODY in a context where any %END-OF-THE-WORLD (thrown e.g.
;;; by QUIT) is caught and any final processing and return codes are
;;; handled appropriately.
(defmacro handling-end-of-the-world (&body body)
  (let ((caught (gensym "CAUGHT")))
    `(let ((,caught (catch '%end-of-the-world
                      (/show0 "inside CATCH '%END-OF-THE-WORLD")
                      ,@body)))
       (/show0 "back from CATCH '%END-OF-THE-WORLD, flushing output")
       (flush-standard-output-streams)
       (/show0 "calling UNIX-EXIT")
       (sb!unix:unix-exit ,caught))))
\f
;;;; working with *CURRENT-ERROR-DEPTH* and *MAXIMUM-ERROR-DEPTH*

;;; INFINITE-ERROR-PROTECT is used by ERROR and friends to keep us out
;;; of hyperspace.
(defmacro infinite-error-protect (&rest forms)
  `(unless (infinite-error-protector)
     (/show0 "back from INFINITE-ERROR-PROTECTOR")
     (let ((*current-error-depth* (1+ *current-error-depth*)))
       (/show0 "in INFINITE-ERROR-PROTECT, incremented error depth")
       ;; arbitrary truncation
       #!+sb-show (sb!debug:backtrace 8)
       ,@forms)))

;;; a helper function for INFINITE-ERROR-PROTECT
(defun infinite-error-protector ()
  (/show0 "entering INFINITE-ERROR-PROTECTOR, *CURRENT-ERROR-DEPTH*=..")
  (/hexstr *current-error-depth*)
  (cond ((not *cold-init-complete-p*)
         (%primitive print "Argh! error in cold init, halting")
         (%primitive sb!c:halt))
        ((or (not (boundp '*current-error-depth*))
             (not (realp   *current-error-depth*))
             (not (boundp '*maximum-error-depth*))
             (not (realp   *maximum-error-depth*)))
         (%primitive print "Argh! corrupted error depth, halting")
         (%primitive sb!c:halt))
        ((> *current-error-depth* *maximum-error-depth*)
         (/show0 "*MAXIMUM-ERROR-DEPTH*=..")
         (/hexstr *maximum-error-depth*)
         (/show0 "in INFINITE-ERROR-PROTECTOR, calling ERROR-ERROR")
         (error-error "Help! "
                      *current-error-depth*
                      " nested errors. "
                      "KERNEL:*MAXIMUM-ERROR-DEPTH* exceeded.")
         t)
        (t
         (/show0 "returning normally from INFINITE-ERROR-PROTECTOR")
         nil)))

;;; FIXME: I had a badly broken version of INFINITE-ERROR-PROTECTOR at
;;; one point (shown below), and SBCL cross-compiled it without
;;; warning about FORMS being undefined. Check whether that problem
;;; (missing warning) is repeatable in the final system and if so, fix
;;; it.
#|
(defun infinite-error-protector ()
  `(cond ((not *cold-init-complete-p*)
          (%primitive print "Argh! error in cold init, halting")
          (%primitive sb!c:halt))
         ((or (not (boundp '*current-error-depth*))
              (not (realp   *current-error-depth*))
              (not (boundp '*maximum-error-depth*))
              (not (realp   *maximum-error-depth*)))
          (%primitive print "Argh! corrupted error depth, halting")
          (%primitive sb!c:halt))
         ((> *current-error-depth* *maximum-error-depth*)
          (/show0 "in INFINITE-ERROR-PROTECTOR, calling ERROR-ERROR")
          (error-error "Help! "
                       *current-error-depth*
                       " nested errors. "
                       "KERNEL:*MAXIMUM-ERROR-DEPTH* exceeded.")
          (progn ,@forms)
          t)
         (t
          (/show0 "in INFINITE-ERROR-PROTECTOR, returning normally")
          nil)))
|#
\f
;;;; miscellaneous external functions

(defun sleep (n)
  #!+sb-doc
  "This function causes execution to be suspended for N seconds. N may
  be any non-negative, non-complex number."
  (when (or (not (realp n))
            (minusp n))
    (error 'simple-type-error
           :format-control "invalid argument to SLEEP: ~S"
           :format-arguments (list n)
           :datum n
           :expected-type '(real 0)))
  (multiple-value-bind (sec usec)
      (if (integerp n)
          (values n 0)
          (multiple-value-bind (sec frac)
              (truncate n)
            (values sec (truncate frac 1e-6))))
    (sb!unix:unix-select 0 0 0 0 sec usec))
  nil)
\f
;;;; SCRUB-CONTROL-STACK

(defconstant bytes-per-scrub-unit 2048)

;;; Zero the unused portion of the control stack so that old objects
;;; are not kept alive because of uninitialized stack variables.

;;; "To summarize the problem, since not all allocated stack frame
;;; slots are guaranteed to be written by the time you call an another
;;; function or GC, there may be garbage pointers retained in your
;;; dead stack locations.  The stack scrubbing only affects the part
;;; of the stack from the SP to the end of the allocated stack."
;;; - ram, on cmucl-imp, Tue, 25 Sep 2001

;;; So, as an (admittedly lame) workaround, from time to time we call
;;; scrub-control-stack to zero out all the unused portion.  This is
;;; supposed to happen when the stack is mostly empty, so that we have
;;; a chance of clearing more of it: callers are currently (2002.07.18)
;;; REPL and SUB-GC

(defun scrub-control-stack ()
  (declare (optimize (speed 3) (safety 0))
           (values (unsigned-byte 20))) ; FIXME: DECLARE VALUES?

  #!-stack-grows-downward-not-upward
  (let* ((csp (sap-int (sb!c::control-stack-pointer-sap)))
         (initial-offset (logand csp (1- bytes-per-scrub-unit)))
         (end-of-stack
          (- sb!vm::*control-stack-end* sb!c:*backend-page-size*)))
    (labels
        ((scrub (ptr offset count)
           (declare (type system-area-pointer ptr)
                    (type (unsigned-byte 16) offset)
                    (type (unsigned-byte 20) count)
                    (values (unsigned-byte 20)))
           (cond ((>= (sap-int ptr) end-of-stack) 0)
                 ((= offset bytes-per-scrub-unit)
                  (look (sap+ ptr bytes-per-scrub-unit) 0 count))
                 (t
                  (setf (sap-ref-32 ptr offset) 0)
                  (scrub ptr (+ offset sb!vm:n-word-bytes) count))))
         (look (ptr offset count)
           (declare (type system-area-pointer ptr)
                    (type (unsigned-byte 16) offset)
                    (type (unsigned-byte 20) count)
                    (values (unsigned-byte 20)))
           (cond ((>= (sap-int ptr) end-of-stack) 0)
                 ((= offset bytes-per-scrub-unit)
                  count)
                 ((zerop (sap-ref-32 ptr offset))
                  (look ptr (+ offset sb!vm:n-word-bytes) count))
                 (t
                  (scrub ptr offset (+ count sb!vm:n-word-bytes))))))
      (declare (type (unsigned-byte 32) csp))
      (scrub (int-sap (- csp initial-offset))
             (* (floor initial-offset sb!vm:n-word-bytes) sb!vm:n-word-bytes)
             0)))

  #!+stack-grows-downward-not-upward
  (let* ((csp (sap-int (sb!c::control-stack-pointer-sap)))
         (end-of-stack (+ sb!vm::*control-stack-start* sb!c:*backend-page-size*))
         (initial-offset (logand csp (1- bytes-per-scrub-unit))))
    (labels
        ((scrub (ptr offset count)
           (declare (type system-area-pointer ptr)
                    (type (unsigned-byte 16) offset)
                    (type (unsigned-byte 20) count)
                    (values (unsigned-byte 20)))
           (let ((loc (int-sap (- (sap-int ptr) (+ offset sb!vm:n-word-bytes)))))
             (cond ((< (sap-int loc) end-of-stack) 0)
                   ((= offset bytes-per-scrub-unit)
                    (look (int-sap (- (sap-int ptr) bytes-per-scrub-unit))
                          0 count))
                   (t ;; need to fix bug in %SET-STACK-REF
                    (setf (sap-ref-32 loc 0) 0)
                    (scrub ptr (+ offset sb!vm:n-word-bytes) count)))))
         (look (ptr offset count)
           (declare (type system-area-pointer ptr)
                    (type (unsigned-byte 16) offset)
                    (type (unsigned-byte 20) count)
                    (values (unsigned-byte 20)))
           (let ((loc (int-sap (- (sap-int ptr) offset))))
             (cond ((< (sap-int loc) end-of-stack) 0)
                   ((= offset bytes-per-scrub-unit)
                    count)
                   ((zerop (sb!kernel::get-lisp-obj-address (stack-ref loc 0)))
                    (look ptr (+ offset sb!vm:n-word-bytes) count))
                   (t
                    (scrub ptr offset (+ count sb!vm:n-word-bytes)))))))
      (declare (type (unsigned-byte 32) csp))
      (scrub (int-sap (+ csp initial-offset))
             (* (floor initial-offset sb!vm:n-word-bytes) sb!vm:n-word-bytes)
             0))))
\f
;;;; the default toplevel function

(defvar / nil
  #!+sb-doc
  "a list of all the values returned by the most recent top level EVAL")
(defvar //  nil #!+sb-doc "the previous value of /")
(defvar /// nil #!+sb-doc "the previous value of //")
(defvar *   nil #!+sb-doc "the value of the most recent top level EVAL")
(defvar **  nil #!+sb-doc "the previous value of *")
(defvar *** nil #!+sb-doc "the previous value of **")
(defvar +   nil #!+sb-doc "the value of the most recent top level READ")
(defvar ++  nil #!+sb-doc "the previous value of +")
(defvar +++ nil #!+sb-doc "the previous value of ++")
(defvar -   nil #!+sb-doc "the form currently being evaluated")

(defun interactive-eval (form)
  "Evaluate FORM, returning whatever it returns and adjusting ***, **, *,
   +++, ++, +, ///, //, /, and -."
  (setf - form)
  (let ((results
         (multiple-value-list
          (eval-in-lexenv form
                          (make-null-interactive-lexenv)))))
    (setf /// //
          // /
          / results
          *** **
          ** *
          * (car results)))
  (setf +++ ++
        ++ +
        + -)
  (unless (boundp '*)
    ;; The bogon returned an unbound marker.
    ;; FIXME: It would be safer to check every one of the values in RESULTS,
    ;; instead of just the first one.
    (setf * nil)
    (cerror "Go on with * set to NIL."
            "EVAL returned an unbound marker."))
  (values-list /))

;;; Flush anything waiting on one of the ANSI Common Lisp standard
;;; output streams before proceeding.
(defun flush-standard-output-streams ()
  (dolist (name '(*debug-io*
                  *error-output*
                  *query-io*
                  *standard-output*
                  *trace-output*))
    (finish-output (symbol-value name)))
  (values))

;;; the default system top level function
(defun toplevel-init ()

  (/show0 "entering TOPLEVEL-INIT")
  (setf sb!thread::*session-lock* (sb!thread:make-mutex :name "the terminal"))
  (sb!thread::get-foreground)
  (let (;; value of --sysinit option
        (sysinit nil)
        ;; value of --userinit option
        (userinit nil)
        ;; values of --eval options, in reverse order; and also any
        ;; other options (like --load) which're translated into --eval
        ;;
        ;; The values are stored as strings, so that they can be
        ;; passed to READ only after their predecessors have been
        ;; EVALed, so that things work when e.g. REQUIRE in one EVAL
        ;; form creates a package referred to in the next EVAL form.
        (reversed-evals nil) 
        ;; Has a --noprint option been seen?
        (noprint nil)        
        ;; everything in *POSIX-ARGV* except for argv[0]=programname
        (options (rest *posix-argv*))) 

    (declare (type list options))

    (/show0 "done with outer LET in TOPLEVEL-INIT")
  
    ;; FIXME: There are lots of ways for errors to happen around here
    ;; (e.g. bad command line syntax, or READ-ERROR while trying to
    ;; READ an --eval string). Make sure that they're handled
    ;; reasonably. Also, perhaps all errors while parsing the command
    ;; line should cause the system to QUIT, instead of trying to go
    ;; into the Lisp debugger, since trying to go into the debugger
    ;; gets into various annoying issues of where we should go after
    ;; the user tries to return from the debugger.
    
    ;; Parse command line options.
    (loop while options do
          (/show0 "at head of LOOP WHILE OPTIONS DO in TOPLEVEL-INIT")
          (let ((option (first options)))
            (flet ((pop-option ()
                     (if options
                         (pop options)
                         (error "unexpected end of command line options"))))
              (cond ((string= option "--sysinit")
                     (pop-option)
                     (if sysinit
                         (error "multiple --sysinit options")
                         (setf sysinit (pop-option))))
                    ((string= option "--userinit")
                     (pop-option)
                     (if userinit
                         (error "multiple --userinit options")
                         (setf userinit (pop-option))))
                    ((string= option "--eval")
                     (pop-option)
                     (push (pop-option) reversed-evals))
                    ((string= option "--load")
                     (pop-option)
                     (push (concatenate 'string "(LOAD \"" (pop-option) "\")")
                           reversed-evals))
                    ((string= option "--noprint")
                     (pop-option)
                     (setf noprint t))
                    ;; FIXME: --noprogrammer was deprecated in 0.7.5, and
                    ;; in a year or so this backwards compatibility can
                    ;; go away.
                    ((string= option "--noprogrammer")
                     (warn "treating deprecated --noprogrammer as --disable-debugger")
                     (pop-option)
                     (push "(DISABLE-DEBUGGER)" reversed-evals))
                    ((string= option "--disable-debugger")
                     (pop-option)
                     (push "(DISABLE-DEBUGGER)" reversed-evals))
                    ((string= option "--end-toplevel-options")
                     (pop-option)
                     (return))
                    (t
                     ;; Anything we don't recognize as a toplevel
                     ;; option must be the start of user-level
                     ;; options.. except that if we encounter
                     ;; "--end-toplevel-options" after we gave up
                     ;; because we didn't recognize an option as a
                     ;; toplevel option, then the option we gave up on
                     ;; must have been an error. (E.g. in
                     ;;  "sbcl --eval '(a)' --eval'(b)' --end-toplevel-options"
                     ;; this test will let us detect that the string
                     ;; "--eval(b)" is an error.)
                     (if (find "--end-toplevel-options" options
                               :test #'string=)
                         (error "bad toplevel option: ~S" (first options))
                         (return)))))))
    (/show0 "done with LOOP WHILE OPTIONS DO in TOPLEVEL-INIT")

    ;; Delete all the options that we processed, so that only
    ;; user-level options are left visible to user code.
    (setf (rest *posix-argv*) options)

    ;; Handle initialization files.
    (/show0 "handling initialization files in TOPLEVEL-INIT")
    (flet (;; If any of POSSIBLE-INIT-FILE-NAMES names a real file,
           ;; return its truename.
           (probe-init-files (&rest possible-init-file-names)
             (declare (type list possible-init-file-names))
             (/show0 "entering PROBE-INIT-FILES")
             (prog1
                 (find-if (lambda (x)
                            (and (stringp x) (probe-file x)))
                          possible-init-file-names)
               (/show0 "leaving PROBE-INIT-FILES"))))
      (let* ((sbcl-home (posix-getenv "SBCL_HOME"))
             (sysinit-truename (if sbcl-home
                                   (probe-init-files sysinit
                                                     (concatenate 'string
                                                                  sbcl-home
                                                                  "/sbclrc"))
                                   (probe-init-files sysinit
                                                     "/etc/sbclrc"
                                                     "/usr/local/etc/sbclrc")))
             (user-home (or (posix-getenv "HOME")
                            (error "The HOME environment variable is unbound, ~
                                    so user init file can't be found.")))
             (userinit-truename (probe-init-files userinit
                                                  (concatenate 'string
                                                               user-home
                                                               "/.sbclrc"))))

        ;; We wrap all the pre-REPL user/system customized startup code 
        ;; in a restart.
        ;;
        ;; (Why not wrap everything, even the stuff above, in this
        ;; restart? Errors above here are basically command line or
        ;; Unix environment errors, e.g. a missing file or a typo on
        ;; the Unix command line, and you don't need to get into Lisp
        ;; to debug them, you should just start over and do it right
        ;; at the Unix level. Errors below here are generally errors
        ;; in user Lisp code, and it might be helpful to let the user
        ;; reach the REPL in order to help figure out what's going
        ;; on.)
        (restart-case
            (progn
              (flet ((process-init-file (truename)
                       (when truename
                         (unless (load truename)
                           (error "~S was not successfully loaded." truename))
                         (flush-standard-output-streams))))
                (process-init-file sysinit-truename)
                (process-init-file userinit-truename))

              ;; Process --eval options.
              (/show0 "handling --eval options in TOPLEVEL-INIT")
              (dolist (expr-as-string (reverse reversed-evals))
                (/show0 "handling one --eval option in TOPLEVEL-INIT")
                (let ((expr (with-input-from-string (eval-stream
                                                     expr-as-string)
                              (let* ((eof-marker (cons :eof :eof))
                                     (result (read eval-stream nil eof-marker))
                                     (eof (read eval-stream nil eof-marker)))
                                (cond ((eq result eof-marker)
                                       (error "unable to parse ~S"
                                              expr-as-string))
                                      ((not (eq eof eof-marker))
                                       (error "more than one expression in ~S"
                                              expr-as-string))
                                      (t
                                       result))))))
                  (eval expr)
                  (flush-standard-output-streams))))
          (continue ()
            :report
            "Continue anyway (skipping to toplevel read/eval/print loop)."
            (/show0 "CONTINUEing from pre-REPL RESTART-CASE")
            (values)) ; (no-op, just fall through)
          (quit ()
            :report "Quit SBCL (calling #'QUIT, killing the process)."
            (/show0 "falling through to QUIT from pre-REPL RESTART-CASE")
            (quit))))

      ;; one more time for good measure, in case we fell out of the
      ;; RESTART-CASE above before one of the flushes in the ordinary
      ;; flow of control had a chance to operate
      (flush-standard-output-streams)

      (/show0 "falling into TOPLEVEL-REPL from TOPLEVEL-INIT")
      (toplevel-repl noprint)
      ;; (classic CMU CL error message: "You're certainly a clever child.":-)
      (critically-unreachable "after TOPLEVEL-REPL"))))

;;; halt-on-failures and prompt-on-failures modes, suitable for
;;; noninteractive and interactive use respectively
(defun disable-debugger ()
  (setf *debugger-hook* 'noprogrammer-debugger-hook-fun
        *debug-io* *error-output*))
(defun enable-debugger ()
  (setf *debugger-hook* nil
        *debug-io* *query-io*))

;;; read-eval-print loop for the default system toplevel
(defun toplevel-repl (noprint)
  (/show0 "entering TOPLEVEL-REPL")
  (let ((* nil) (** nil) (*** nil)
        (- nil)
        (+ nil) (++ nil) (+++ nil)
        (/// nil) (// nil) (/ nil))
    ;; WITH-SIMPLE-RESTART doesn't actually restart its body as some
    ;; (like WHN for an embarrassingly long time ca. 2001-12-07) might
    ;; think, but instead drops control back out at the end. So when a
    ;; TOPLEVEL or outermost-ABORT restart happens, we need this outer
    ;; LOOP wrapper to grab control and start over again. (And it also
    ;; wraps CATCH 'TOPLEVEL-CATCHER for similar reasons.)
    (loop
     (/show0 "about to set up restarts in TOPLEVEL-REPL")
     ;; There should only be one TOPLEVEL restart, and it's here, so
     ;; restarting at TOPLEVEL always bounces you all the way out here.
     (with-simple-restart (toplevel
                           "Restart at toplevel READ/EVAL/PRINT loop.")
       ;; We add a new ABORT restart for every debugger level, so 
       ;; restarting at ABORT in a nested debugger gets you out to the
       ;; innermost enclosing debugger, and only when you're in the
       ;; outermost, unnested debugger level does restarting at ABORT 
       ;; get you out to here.
       (with-simple-restart
           (abort
            "~@<Reduce debugger level (leaving debugger, returning to toplevel).~@:>")
         (catch 'toplevel-catcher
           #!-sunos (sb!unix:unix-sigsetmask 0) ; FIXME: What is this for?
           ;; in the event of a control-stack-exhausted-error, we should
           ;; have unwound enough stack by the time we get here that this
           ;; is now possible
           (sb!kernel::protect-control-stack-guard-page 1)
           (repl noprint)
           (critically-unreachable "after REPL")))))))

;;; Our default REPL prompt is the minimal traditional one.
(defun repl-prompt-fun (stream)
  (fresh-line stream)
  (write-string "* " stream)) ; arbitrary but customary REPL prompt

;;; Our default form reader does relatively little magic, but does
;;; handle the Unix-style EOF-is-end-of-process convention.
(defun repl-read-form-fun (in out)
  (declare (type stream in out) (ignore out))
  (let* ((eof-marker (cons nil nil))
         (form (read in nil eof-marker)))
    (if (eq form eof-marker)
        (quit)
        form)))

;;; hooks to support customized toplevels like ACL-style toplevel
;;; from KMR on sbcl-devel 2002-12-21
(defvar *repl-read-form-fun* #'repl-read-form-fun
  "a function of two stream arguments IN and OUT for the toplevel REPL to
  call: Return the next Lisp form to evaluate (possibly handling other
  magic -- like ACL-style keyword commands -- which precede the next
  Lisp form). The OUT stream is there to support magic which requires
  issuing new prompts.")
(defvar *repl-prompt-fun* #'repl-prompt-fun
  "a function of one argument STREAM for the toplevel REPL to call: Prompt
  the user for input.")

(defun repl (noprint)
  (/show0 "entering REPL")
  (loop
   ;; (See comment preceding the definition of SCRUB-CONTROL-STACK.)
   (scrub-control-stack)
   (unless noprint
     (funcall *repl-prompt-fun* *standard-output*)
     ;; (Should *REPL-PROMPT-FUN* be responsible for doing its own
     ;; FORCE-OUTPUT? I can't imagine a valid reason for it not to
     ;; be done here, so leaving it up to *REPL-PROMPT-FUN* seems
     ;; odd. But maybe there *is* a valid reason in some
     ;; circumstances? perhaps some deadlock issue when being driven
     ;; by another process or something...)
     (force-output *standard-output*))
   (let* ((form (funcall *repl-read-form-fun*
                         *standard-input*
                         *standard-output*))
          (results (multiple-value-list (interactive-eval form))))
     (unless noprint
       (dolist (result results)
         (fresh-line)
         (prin1 result))))))

;;; suitable value for *DEBUGGER-HOOK* for a noninteractive Unix-y program
(defun noprogrammer-debugger-hook-fun (condition old-debugger-hook)
  (declare (ignore old-debugger-hook))
  (flet ((failure-quit (&key recklessly-p)
           (/show0 "in FAILURE-QUIT (in --disable-debugger debugger hook)")
           (quit :unix-status 1 :recklessly-p recklessly-p)))
    ;; This HANDLER-CASE is here mostly to stop output immediately
    ;; (and fall through to QUIT) when there's an I/O error. Thus,
    ;; when we're run under a shell script or something, we can die
    ;; cleanly when the script dies (and our pipes are cut), instead
    ;; of falling into ldb or something messy like that.
    (handler-case
        (progn
          (format *error-output*
                  "~&~@<unhandled condition (of type ~S): ~2I~_~A~:>~2%"
                  (type-of condition)
                  condition)
          ;; Flush *ERROR-OUTPUT* even before the BACKTRACE, so that
          ;; even if we hit an error within BACKTRACE (e.g. a bug in
          ;; the debugger's own frame-walking code, or a bug in a user
          ;; PRINT-OBJECT method) we'll at least have the CONDITION
          ;; printed out before we die.
          (finish-output *error-output*)
          ;; (Where to truncate the BACKTRACE is of course arbitrary, but
          ;; it seems as though we should at least truncate it somewhere.)
          (sb!debug:backtrace 128 *error-output*)
          (format
           *error-output*
           "~%unhandled condition in --disable-debugger mode, quitting~%")
          (finish-output *error-output*)
          (failure-quit))
      (condition ()
        ;; We IGNORE-ERRORS here because even %PRIMITIVE PRINT can
        ;; fail when our output streams are blown away, as e.g. when
        ;; we're running under a Unix shell script and it dies somehow
        ;; (e.g. because of a SIGINT). In that case, we might as well
        ;; just give it up for a bad job, and stop trying to notify
        ;; the user of anything.
        ;;
        ;; Actually, the only way I've run across to exercise the
        ;; problem is to have more than one layer of shell script.
        ;; I have a shell script which does
        ;;   time nice -10 sh make.sh "$1" 2>&1 | tee make.tmp
        ;; and the problem occurs when I interrupt this with Ctrl-C
        ;; under Linux 2.2.14-5.0 and GNU bash, version 1.14.7(1).
        ;; I haven't figured out whether it's bash, time, tee, Linux, or
        ;; what that is responsible, but that it's possible at all
        ;; means that we should IGNORE-ERRORS here. -- WHN 2001-04-24
        (ignore-errors
         (%primitive print
                     "Argh! error within --disable-debugger error handling"))
        (failure-quit :recklessly-p t)))))
\f
;;; a convenient way to get into the assembly-level debugger
(defun %halt ()
  (%primitive sb!c:halt))