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+;; cus-print.el -- handles print-level and print-circle.
+
+;; LCD Archive Entry:
+;; custom-print|Daniel LaLiberte|liberte@cs.uiuc.edu
+;; |Handle print-level, print-circle and more.
+;; |$Date: Tue Mar 17, 1992$|$Revision: 1.0$|
+
+;; Copyright (C) 1992 Free Software Foundation, Inc.
+
+;; This file is part of GNU Emacs.
+
+;; GNU Emacs is free software; you can redistribute it and/or modify
+;; it under the terms of the GNU General Public License as published by
+;; the Free Software Foundation; either version 1, or (at your option)
+;; any later version.
+
+;; GNU Emacs is distributed in the hope that it will be useful,
+;; but WITHOUT ANY WARRANTY; without even the implied warranty of
+;; MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+;; GNU General Public License for more details.
+
+;; You should have received a copy of the GNU General Public License
+;; along with GNU Emacs; see the file COPYING.  If not, write to
+;; the Free Software Foundation, 675 Mass Ave, Cambridge, MA 02139, USA.
+
+;; This package provides a general print handler for prin1 and princ
+;; that supports print-level and print-circle, and by the way,
+;; print-length since the standard routines are being replaced.  Also,
+;; to print custom types constructed from lists and vectors, use
+;; custom-print-list and custom-print-vector.  See the documentation
+;; strings of these variables for more details.  
+
+;; If the results of your expressions contain circular references to
+;; other parts of the same structure, the standard Emacs print
+;; subroutines may fail to print with an untrappable error,
+;; "Apparently circular structure being printed".  If you only use cdr
+;; circular lists (where cdrs of lists point back; what is the right
+;; term here?), you can limit the length of printing with
+;; print-length.  But car circular lists and circular vectors generate
+;; the above mentioned untrappable error in Emacs version 18.  Version
+;; 19 will support print-level, but it is often useful to get a better
+;; print representation of circular structures; the print-circle
+;; option may be used to print more concise representations.
+
+;; There are two main ways to use this package.  First, you may
+;; replace prin1, princ, and some subroutines that use them by calling
+;; install-custom-print-funcs so that any use of these functions in
+;; lisp code will be affected.  Second, you could call the custom
+;; routines directly, thus only affecting the printing that requires
+;; them.
+
+;; Note that subroutines which call print subroutines directly will not
+;; use the custom print functions.  In particular, the evaluation
+;; functions like eval-region call the print subroutines directly.
+;; Therefore, evaluating (aref circ-list 0), which calls error
+;; directly (because circ-list is not an array), will jump to the top
+;; level instead of printing the circular list.
+
+;; Obviously the right way to implement this custom-print facility
+;; is in C.  Please volunteer since I don't have the time or need.
+
+;; Implementation design: we want to use the same list and vector
+;; processing algorithm for all versions of prin1 and princ, since how
+;; the processing is done depends on print-length, print-level, and
+;; print-circle.  For circle printing, a preprocessing step is
+;; required before the final printing.  Thanks to Jamie Zawinski
+;; for motivation and algorithms.
+
+;;=========================================================
+;; export list:
+
+;; print-level
+;; print-circle
+
+;; custom-print-list
+;; custom-print-vector
+;; add-custom-print-list
+;; add-custom-print-vector
+
+;; install-custom-print-funcs
+;; uninstall-custom-print-funcs
+
+;; custom-prin1
+;; custom-princ
+;; custom-prin1-to-string
+;; custom-print
+;; custom-format
+;; custom-message
+;; custom-error
+
+
+(provide 'custom-print)
+;; Abbreviated package name: "CP"
+
+;;(defvar print-length nil
+;;  "*Controls how many elements of a list, at each level, are printed.
+;;This is defined by emacs.")
+
+(defvar print-level nil
+  "*Controls how many levels deep a nested data object will print.  
+
+If nil, printing proceeds recursively and may lead to
+max-lisp-eval-depth being exceeded or an untrappable error may occur:
+\"Apparently circular structure being printed.\"   Also see
+print-length and print-circle.
+
+If non-nil, components at levels equal to or greater than print-level
+are printed simply as \"#\".  The object to be printed is at level 0,
+and if the object is a list or vector, its top-level components are at
+level 1.")
+
+
+(defvar print-circle nil
+  "*Controls the printing of recursive structures.  
+
+If nil, printing proceeds recursively and may lead to
+max-lisp-eval-depth being exceeded or an untrappable error may occur:
+\"Apparently circular structure being printed.\"  Also see
+print-length and print-level.
+
+If non-nil, shared substructures anywhere in the structure are printed
+with \"#n=\" before the first occurance (in the order of the print
+representation) and \"#n#\" in place of each subsequent occurance,
+where n is a positive decimal integer.
+
+Currently, there is no way to read this representation in Emacs.")
+
+
+(defconst custom-print-list
+  nil
+  ;; e.g.  '((floatp . float-to-string))
+  "If non-nil, an alist for printing of custom list objects.  
+Pairs are of the form (pred . converter).  If the predicate is true
+for an object, the converter is called with the object and should
+return a string which will be printed with princ.  
+Also see custom-print-vector.")
+
+(defconst custom-print-vector
+  nil
+  "If non-nil, an alist for printing of custom vector objects.  
+Pairs are of the form (pred . converter).  If the predicate is true
+for an object, the converter is called with the object and should
+return a string which will be printed with princ.  
+Also see custom-print-list.")
+
+
+(defun add-custom-print-list (pred converter)
+  "Add the pair, a PREDICATE and a CONVERTER, to custom-print-list.
+Any pair that has the same PREDICATE is first removed."
+  (setq custom-print-list (cons (cons pred converter) 
+				(delq (assq pred custom-print-list)
+				      custom-print-list))))
+;; e.g. (add-custom-print-list 'floatp 'float-to-string)
+
+
+(defun add-custom-print-vector (pred converter)
+  "Add the pair, a PREDICATE and a CONVERTER, to custom-print-vector.
+Any pair that has the same PREDICATE is first removed."
+  (setq custom-print-vector (cons (cons pred converter) 
+				  (delq (assq pred custom-print-vector)
+					custom-print-vector))))
+
+
+;;====================================================
+;; Saving and restoring internal printing routines.
+
+(defun CP::set-function-cell (symbol-pair)
+  (fset (car symbol-pair) 
+	(symbol-function (car (cdr symbol-pair)))))
+
+
+(if (not (fboundp 'CP::internal-prin1))
+    (mapcar 'CP::set-function-cell
+	    '((CP::internal-prin1 prin1)
+	      (CP::internal-princ princ)
+	      (CP::internal-print print)
+	      (CP::internal-prin1-to-string prin1-to-string)
+	      (CP::internal-format format)
+	      (CP::internal-message message)
+	      (CP::internal-error error))))
+
+
+(defun install-custom-print-funcs ()
+  "Replace print functions with general, customizable, lisp versions.
+The internal subroutines are saved away and may be recovered with
+uninstall-custom-print-funcs."
+  (interactive)
+  (mapcar 'CP::set-function-cell
+	  '((prin1 custom-prin1)
+	    (princ custom-princ)
+	    (print custom-print)
+	    (prin1-to-string custom-prin1-to-string)
+	    (format custom-format)
+	    (message custom-message)
+	    (error custom-error)
+	    )))
+  
+(defun uninstall-custom-print-funcs ()
+  "Reset print functions to their internal subroutines."
+  (interactive)
+  (mapcar 'CP::set-function-cell
+	  '((prin1 CP::internal-prin1)
+	    (princ CP::internal-princ)
+	    (print CP::internal-print)
+	    (prin1-to-string CP::internal-prin1-to-string)
+	    (format CP::internal-format)
+	    (message CP::internal-message)
+	    (error CP::internal-error)
+	    )))
+
+
+;;===============================================================
+;; Lisp replacements for prin1 and princ and for subrs that use prin1 
+;; (or princ) -- so far only the printing and formatting subrs.
+
+(defun custom-prin1 (object &optional stream)
+  "Replacement for standard prin1 that uses the appropriate
+printer depending on the values of print-level and print-circle (which see).
+
+Output the printed representation of OBJECT, any Lisp object.
+Quoting characters are printed when needed to make output that `read'
+can handle, whenever this is possible.
+Output stream is STREAM, or value of `standard-output' (which see)."
+  (CP::top-level object stream 'CP::internal-prin1))
+
+
+(defun custom-princ (object &optional stream)
+  "Same as custom-prin1 except no quoting."
+  (CP::top-level object stream 'CP::internal-princ))
+
+(defun custom-prin1-to-string-func (c)
+  "Stream function for custom-prin1-to-string."
+  (setq prin1-chars (cons c prin1-chars)))
+
+(defun custom-prin1-to-string (object)
+  "Replacement for standard prin1-to-string."
+  (let ((prin1-chars nil))
+    (custom-prin1 object 'custom-prin1-to-string-func)
+    (concat (nreverse prin1-chars))))
+
+
+(defun custom-print (object &optional stream)
+  "Replacement for standard print."
+  (CP::internal-princ "\n")
+  (custom-prin1 object stream)
+  (CP::internal-princ "\n"))
+
+
+(defun custom-format (fmt &rest args)
+  "Replacement for standard format.
+
+Calls format after first making strings for list or vector args.
+The format specification for such args should be %s in any case, so a
+string argument will also work.  The string is generated with
+custom-prin1-to-string, which quotes quotable characters."
+  (apply 'CP::internal-format fmt
+	 (mapcar (function (lambda (arg)
+			     (if (or (listp arg) (vectorp arg))
+				 (custom-prin1-to-string arg)
+			       arg)))
+		 args)))
+	    
+  
+
+(defun custom-message (fmt &rest args)
+  "Replacement for standard message that works like custom-format."
+  ;; It doesnt work to princ the result of custom-format
+  ;; because the echo area requires special handling
+  ;; to avoid duplicating the output.  CP::internal-message does it right.
+  ;; (CP::internal-princ (apply 'custom-format fmt args))
+  (apply 'CP::internal-message  fmt
+	 (mapcar (function (lambda (arg)
+			     (if (or (listp arg) (vectorp arg))
+				 (custom-prin1-to-string arg)
+			       arg)))
+		 args)))
+	    
+
+(defun custom-error (fmt &rest args)
+  "Replacement for standard error that uses custom-format"
+  (signal 'error (list (apply 'custom-format fmt args))))
+
+
+;;=========================================
+;; Support for custom prin1 and princ
+
+(defun CP::top-level (object stream internal-printer)
+  "Set up for printing."
+  (let ((standard-output (or stream standard-output))
+	(circle-table (and print-circle (CP::preprocess-circle-tree object)))
+	(level (or print-level -1))
+	)
+
+    (fset 'CP::internal-printer internal-printer)
+    (fset 'CP::low-level-prin 
+	  (cond
+	   ((or custom-print-list
+		custom-print-vector
+		print-level ; comment out for version 19
+		)
+	    'CP::custom-object)
+	   (circle-table
+	    'CP::object)
+	   (t 'CP::internal-printer)))
+    (fset 'CP::prin (if circle-table 'CP::circular 'CP::low-level-prin))
+
+    (CP::prin object)
+    object))
+
+
+(defun CP::object (object)
+  "Test object type and print accordingly."
+  ;; Could be called as either CP::low-level-prin or CP::prin.
+  (cond 
+   ((null object) (CP::internal-printer object))
+   ((consp object) (CP::list object))
+   ((vectorp object) (CP::vector object))
+   ;; All other types, just print.
+   (t (CP::internal-printer object))))
+
+
+(defun CP::custom-object (object)
+  "Test object type and print accordingly."
+  ;; Could be called as either CP::low-level-prin or CP::prin.
+  (cond 
+   ((null object) (CP::internal-printer object))
+
+   ((consp object) 
+    (or (and custom-print-list
+	     (CP::custom-object1 object custom-print-list))
+	(CP::list object)))
+
+   ((vectorp object) 
+    (or (and custom-print-vector
+	     (CP::custom-object1 object custom-print-vector))
+	(CP::vector object)))
+
+   ;; All other types, just print.
+   (t (CP::internal-printer object))))
+
+
+(defun CP::custom-object1 (object alist)
+  "Helper for CP::custom-object.
+Print the custom OBJECT using the custom type ALIST.
+For the first predicate that matches the object, the corresponding
+converter is evaluated with the object and the string that results is
+printed with princ.  Return nil if no predicte matches the object."
+  (while (and alist (not (funcall (car (car alist)) object)))
+    (setq alist (cdr alist)))
+  ;; If alist is not null, then something matched.
+  (if alist
+      (CP::internal-princ
+       (funcall (cdr (car alist)) object) ; returns string
+       )))
+
+
+(defun CP::circular (object)
+  "Printer for prin1 and princ that handles circular structures.
+If OBJECT appears multiply, and has not yet been printed,
+prefix with label; if it has been printed, use #n# instead.
+Otherwise, print normally."
+  (let ((tag (assq object circle-table)))
+    (if tag
+	(let ((id (cdr tag)))
+	  (if (> id 0)
+	      (progn
+		;; Already printed, so just print id.
+		(CP::internal-princ "#")
+		(CP::internal-princ id)
+		(CP::internal-princ "#"))
+	    ;; Not printed yet, so label with id and print object.
+	    (setcdr tag (- id)) ; mark it as printed
+	    (CP::internal-princ "#")
+	    (CP::internal-princ (- id))
+	    (CP::internal-princ "=")
+	    (CP::low-level-prin object)
+	    ))
+      ;; Not repeated in structure.
+      (CP::low-level-prin object))))
+
+
+;;================================================
+;; List and vector processing for print functions.
+
+(defun CP::list (list)
+  "Print a list using print-length, print-level, and print-circle."
+  (if (= level 0)
+      (CP::internal-princ "#")
+    (let ((level (1- level)))
+      (CP::internal-princ "(")
+      (let ((length (or print-length 0)))
+
+	;; Print the first element always (even if length = 0).
+	(CP::prin (car list))
+	(setq list (cdr list))
+	(if list (CP::internal-princ " "))
+	(setq length (1- length))
+
+	;; Print the rest of the elements.
+	(while (and list (/= 0 length))
+	  (if (and (listp list)
+		   (not (assq list circle-table)))
+	      (progn
+		(CP::prin (car list))
+		(setq list (cdr list)))
+
+	    ;; cdr is not a list, or it is in circle-table.
+	    (CP::internal-princ ". ")
+	    (CP::prin list)
+	    (setq list nil))
+
+	  (setq length (1- length))
+	  (if list (CP::internal-princ " ")))
+
+	(if (and list (= length 0)) (CP::internal-princ "..."))
+	(CP::internal-princ ")"))))
+  list)
+
+
+(defun CP::vector (vector)
+  "Print a vector using print-length, print-level, and print-circle."
+  (if (= level 0)
+      (CP::internal-princ "#")
+    (let ((level (1- level))
+	  (i 0)
+	  (len (length vector)))
+      (CP::internal-princ "[")
+
+      (if print-length
+	  (setq len (min print-length len)))
+      ;; Print the elements
+      (while (< i len)
+	(CP::prin (aref vector i))
+	(setq i (1+ i))
+	(if (< i (length vector)) (CP::internal-princ " ")))
+
+      (if (< i (length vector)) (CP::internal-princ "..."))
+      (CP::internal-princ "]")
+      ))
+  vector)
+
+
+;;==================================
+;; Circular structure preprocessing
+
+(defun CP::preprocess-circle-tree (object)
+  ;; Fill up the table.  
+  (let (;; Table of tags for each object in an object to be printed.
+	;; A tag is of the form:
+	;; ( <object> <nil-t-or-id-number> )
+	;; The id-number is generated after the entire table has been computed.
+	;; During walk through, the real circle-table lives in the cdr so we
+	;; can use setcdr to add new elements instead of having to setq the
+	;; variable sometimes (poor man's locf).
+	(circle-table (list nil)))
+    (CP::walk-circle-tree object)
+
+    ;; Reverse table so it is in the order that the objects will be printed.
+    ;; This pass could be avoided if we always added to the end of the
+    ;; table with setcdr in walk-circle-tree.
+    (setcdr circle-table (nreverse (cdr circle-table)))
+
+    ;; Walk through the table, assigning id-numbers to those
+    ;; objects which will be printed using #N= syntax.  Delete those
+    ;; objects which will be printed only once (to speed up assq later).
+    (let ((rest circle-table)
+	  (id -1))
+      (while (cdr rest)
+	(let ((tag (car (cdr rest))))
+	  (cond ((cdr tag)
+		 (setcdr tag id)
+		 (setq id (1- id))
+		 (setq rest (cdr rest)))
+		;; Else delete this object.
+		(t (setcdr rest (cdr (cdr rest))))))
+	))
+    ;; Drop the car.
+    (cdr circle-table)
+    ))
+
+
+
+(defun CP::walk-circle-tree (object)
+  (let (read-equivalent-p tag)
+    (while object
+      (setq read-equivalent-p (or (numberp object) (symbolp object))
+	    tag (and (not read-equivalent-p)
+		     (assq object (cdr circle-table))))
+      (cond (tag
+	     ;; Seen this object already, so note that.
+	     (setcdr tag t))
+
+	    ((not read-equivalent-p)
+	     ;; Add a tag for this object.
+	     (setcdr circle-table
+		     (cons (list object)
+			   (cdr circle-table)))))
+      (setq object
+	    (cond 
+	     (tag ;; No need to descend since we have already.
+	      nil)
+
+	     ((consp object)
+	      ;; Walk the car of the list recursively.
+	      (CP::walk-circle-tree (car object))
+	      ;; But walk the cdr with the above while loop
+	      ;; to avoid problems with max-lisp-eval-depth.
+	      ;; And it should be faster than recursion.
+	      (cdr object))
+
+	     ((vectorp object)
+	      ;; Walk the vector.
+	      (let ((i (length object))
+		    (j 0))
+		(while (< j i)
+		  (CP::walk-circle-tree (aref object j))
+		  (setq j (1+ j))))))))))
+
+
+
+;;=======================================
+
+(quote 
+ examples
+ 
+ (progn
+   ;; Create some circular structures.
+   (setq circ-sym (let ((x (make-symbol "FOO"))) (list x x)))
+   (setq circ-list (list 'a 'b (vector 1 2 3 4) 'd 'e 'f))
+   (setcar (nthcdr 3 circ-list) circ-list)
+   (aset (nth 2 circ-list) 2 circ-list)
+   (setq dotted-circ-list (list 'a 'b 'c))
+   (setcdr (cdr (cdr dotted-circ-list)) dotted-circ-list)
+   (setq circ-vector (vector 1 2 3 4 (list 'a 'b 'c 'd) 6 7))
+   (aset circ-vector 5 (make-symbol "-gensym-"))
+   (setcar (cdr (aref circ-vector 4)) (aref circ-vector 5))
+   nil)
+
+ (install-custom-print-funcs)
+ ;; (setq print-circle t)
+
+ (let ((print-circle t))
+   (or (equal (prin1-to-string circ-list) "#1=(a b [1 2 #1# 4] #1# e f)")
+       (error "circular object with array printing")))
+
+ (let ((print-circle t))
+   (or (equal (prin1-to-string dotted-circ-list) "#1=(a b c . #1#)")
+       (error "circular object with array printing")))
+
+ (let* ((print-circle t)
+	(x (list 'p 'q))
+	(y (list (list 'a 'b) x 'foo x)))
+   (setcdr (cdr (cdr (cdr y))) (cdr y))
+   (or (equal (prin1-to-string y) "((a b) . #1=(#2=(p q) foo #2# . #1#))"
+	      )
+       (error "circular list example from CL manual")))
+
+ ;; There's no special handling of uninterned symbols in custom-print.
+ (let ((print-circle nil))
+   (or (equal (prin1-to-string circ-sym) "(#:FOO #:FOO)")
+       (error "uninterned symbols in list")))
+ (let ((print-circle t))
+   (or (equal (prin1-to-string circ-sym) "(#1=FOO #1#)")
+       (error "circular uninterned symbols in list")))
+
+ (uninstall-custom-print-funcs)
+ )
+
+;;; cus-print.el ends here