Implement print-circle, allowing recursive and circular structures to be read. src/ChangeLog addition: 2011-09-04 Aidan Kehoe <kehoea@parhasard.net> * alloc.c: * alloc.c (ALLOC_FROB_BLOCK_LISP_OBJECT_1): * alloc.c (ALLOC_FROB_BLOCK_LISP_OBJECT): * alloc.c (cons_print_preprocess): * alloc.c (vector_print_preprocess): * alloc.c (vector_nsubst_structures_descend): * alloc.c (Fmake_symbol): * alloc.c (UNMARK_symbol): * alloc.c (sweep_symbols): * alloc.c (reinit_alloc_objects_early): * alloc.c (reinit_alloc_early): * bytecode.c: * bytecode.c (compiled_function_print_preprocess): * bytecode.c (compiled_function_nsubst_structures_descend): * bytecode.c (set_compiled_function_arglist): * bytecode.c (set_compiled_function_interactive): * bytecode.c (bytecode_objects_create): * chartab.c: * chartab.c (print_preprocess_mapper): * chartab.c (nsubst_structures_mapper): * chartab.c (char_table_nsubst_structures_descend): * chartab.c (chartab_objects_create): * elhash.c: * elhash.c (nsubst_structures_map_hash_table): * elhash.c (hash_table_nsubst_structures_descend): * elhash.c (print_preprocess_mapper): * elhash.c (hash_table_print_preprocess): * elhash.c (inchash_eq): * elhash.c (hash_table_objects_create): * elhash.c (syms_of_elhash): * elhash.h: * emacs.c (main_1): * fns.c: * fns.c (check_eq_nokey): * fns.c (Fnsubst): * fns.c (syms_of_fns): * lisp.h: * lisp.h (struct Lisp_Symbol): * lisp.h (IN_OBARRAY): * lisp.h (struct): * lisp.h (PRINT_PREPROCESS): * lread.c (read1): * lrecord.h: * lrecord.h (struct lrecord_implementation): * lrecord.h (DEFINE_DUMPABLE_MODULE_LISP_OBJECT): * print.c: * print.c (PRINT_CIRCLE_LIMIT): * print.c (print_continuous_numbering_changed): * print.c (print_prepare): * print.c (print_finish): * print.c (Fprin1_to_string): * print.c (print_cons): * print.c (print_preprocess_inchash_eq): * print.c (print_preprocess): * print.c (print_sort_get_numbers): * print.c (print_sort_compare_ordinals): * print.c (print_gensym_or_circle): * print.c (nsubst_structures_descend): * print.c (nsubst_structures): * print.c (print_internal): * print.c (print_symbol): * print.c (vars_of_print): * rangetab.c: * rangetab.c (range_table_print_preprocess): * rangetab.c (range_table_nsubst_structures_descend): * rangetab.c (rangetab_objects_create): * rangetab.c (syms_of_rangetab): * symbols.c: * symbols.c (symbol_print_preprocess): * symbols.c (Fintern): * symbols.c (Funintern): * symbols.c (reinit_symbol_objects_early): * symbols.c (init_symbols_once_early): * symsinit.h: Implement print-circle, printing circular structures in a readable fashion, and treating them appropriately on read. This is by means of two new object methods, print_preprocess (detecting circularities), and nsubst_structures_descend (replacing placeholders with the read objects). Expose the substitution to Lisp via #'nsubst and its new :descend-structures keyword. Store information as to whether symbols are interned in obarray or not in their header, making checking for keywords and uninterned symbols (and thus printing) cheaper. Default print_gensym to t, as Common Lisp does, and as a more-than-decade old comment suggests. lisp/ChangeLog addition: 2011-09-04 Aidan Kehoe <kehoea@parhasard.net> * bytecomp.el (byte-compile-output-file-form): * bytecomp.el (byte-compile-output-docform): Bind print-circle, print-continuous-numbering in these functions, now those variables are available. * lisp.el (forward-sexp): * lisp.el (backward-sexp): Recognise leading #N= as being part of an expression. tests/ChangeLog addition: 2011-09-04 Aidan Kehoe <kehoea@parhasard.net> * automated/lisp-reader-tests.el: * automated/lisp-tests.el (literal-with-uninterned): * automated/symbol-tests.el (foo): Test print-circle, for printing (mutually-)recursive and circular structures. Bind print-continuous-numbering where appropriate.

--- a/lisp/bytecomp.el	Sun Aug 28 10:34:54 2011 +0100
+++ b/lisp/bytecomp.el	Sun Sep 04 19:51:35 2011 +0100
@@ -1935,12 +1935,13 @@
       (byte-compile-output-docform nil nil '("\n(" 3 ")") form nil
 				   (memq (car form)
 					 '(autoload custom-declare-variable)))
-    (let ((print-escape-newlines t)
-	  (print-length nil)
-	  (print-level nil)
-	  (print-readably t)	; print #[] for bytecode, 'x for (quote x)
-	  (print-gensym (if byte-compile-print-gensym '(t) nil))
-          print-gensym-alist)
+    (let* ((print-escape-newlines t)
+	   (print-length nil)
+	   (print-level nil)
+	   (print-readably t)	; print #[] for bytecode, 'x for (quote x)
+	   (print-gensym byte-compile-print-gensym)
+	   (print-continuous-numbering print-gensym)
+	   (print-circle t))
       (when byte-compile-output-preface
         (princ "\n(progn " byte-compile-outbuffer)
         (prin1 byte-compile-output-preface byte-compile-outbuffer))
@@ -1984,18 +1985,16 @@
 			 (> (length (nth (nth 1 info) form)) 0)
 			 (char= (aref (nth (nth 1 info) form) 0) ?*))
 		    (setq position (- position)))))
-	 (let ((print-escape-newlines t)
-	       (print-readably t)	; print #[] for bytecode, 'x for (quote x)
-	       ;; Use a cons cell to say that we want
-	       ;; print-gensym-alist not to be cleared between calls
-	       ;; to print functions.
-	       (print-gensym (if byte-compile-print-gensym '(t) nil))
-	       print-gensym-alist
-	       (index 0))
+         (byte-compile-flush-pending)
+	 (let* ((print-escape-newlines t)
+		(print-readably t)	; print #[] for bytecode, 'x for (quote x)
+		(print-gensym byte-compile-print-gensym)
+                (print-continuous-numbering print-gensym)
+                (print-circle t)
+		(index 0))
            (when byte-compile-output-preface
              (princ "\n(progn " byte-compile-outbuffer)
              (prin1 byte-compile-output-preface byte-compile-outbuffer))
-	   (byte-compile-flush-pending)
 	   (if preface
 	       (progn
 		 (insert preface)