+;;; Oh, what a tangled web we weave when we preserve backwards
+;;; compatibility with 1968-style use of global variables to control
+;;; per-stream i/o properties; there's really no way to get this
+;;; quite right, but we do what we can.
+(defun funcall-with-debug-io-syntax (fun &rest rest)
+ (declare (type function fun))
+ ;; Try to force the other special variables into a useful state.
+ (let (;; Protect from WITH-STANDARD-IO-SYNTAX some variables where
+ ;; any default we might use is less useful than just reusing
+ ;; the global values.
+ (original-package *package*)
+ (original-print-pretty *print-pretty*))
+ (with-standard-io-syntax
+ (let (;; We want the printer and reader to be in a useful state,
+ ;; regardless of where the debugger was invoked in the
+ ;; program. WITH-STANDARD-IO-SYNTAX did much of what we
+ ;; want, but
+ ;; * It doesn't affect our internal special variables
+ ;; like *CURRENT-LEVEL-IN-PRINT*.
+ ;; * It isn't customizable.
+ ;; * It doesn't set *PRINT-READABLY* to the same value
+ ;; as the toplevel default.
+ ;; * It sets *PACKAGE* to COMMON-LISP-USER, which is not
+ ;; helpful behavior for a debugger.
+ ;; * There's no particularly good debugger default for
+ ;; *PRINT-PRETTY*, since T is usually what you want
+ ;; -- except absolutely not what you want when you're
+ ;; debugging failures in PRINT-OBJECT logic.
+ ;; We try to address all these issues with explicit
+ ;; rebindings here.
+ (sb!kernel:*current-level-in-print* 0)
+ (*package* original-package)
+ (*print-pretty* original-print-pretty)
+ (*print-readably* nil)
+ ;; Clear the circularity machinery to try to to reduce the
+ ;; pain from sharing the circularity table across all
+ ;; streams; if these are not rebound here, then setting
+ ;; *PRINT-CIRCLE* within the debugger when debugging in a
+ ;; state where something circular was being printed (e.g.,
+ ;; because the debugger was entered on an error in a
+ ;; PRINT-OBJECT method) makes a hopeless mess. Binding them
+ ;; here does seem somewhat ugly because it makes it more
+ ;; difficult to debug the printing-of-circularities code
+ ;; itself; however, as far as I (WHN, 2004-05-29) can see,
+ ;; that's almost entirely academic as long as there's one
+ ;; shared *C-H-T* for all streams (i.e., it's already
+ ;; unreasonably difficult to debug print-circle machinery
+ ;; given the buggy crosstalk between the debugger streams
+ ;; and the stream you're trying to watch), and any fix for
+ ;; that buggy arrangement will likely let this hack go away
+ ;; naturally.
+ (sb!impl::*circularity-hash-table* . nil)
+ (sb!impl::*circularity-counter* . nil)
+ ;; These rebindings are now (as of early 2004) deprecated,
+ ;; with the new *PRINT-VAR-ALIST* mechanism preferred.
+ (*print-length* *debug-print-length*)
+ (*print-level* *debug-print-level*)
+ (*readtable* *debug-readtable*))
+ (progv
+ ;; (Why NREVERSE? PROGV makes the later entries have
+ ;; precedence over the earlier entries.
+ ;; *DEBUG-PRINT-VARIABLE-ALIST* is called an alist, so it's
+ ;; expected that its earlier entries have precedence. And
+ ;; the earlier-has-precedence behavior is mostly more
+ ;; convenient, so that programmers can use PUSH or LIST* to
+ ;; customize *DEBUG-PRINT-VARIABLE-ALIST*.)
+ (nreverse (mapcar #'car *debug-print-variable-alist*))
+ (nreverse (mapcar #'cdr *debug-print-variable-alist*))
+ (apply fun rest))))))
+