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/tests/automated/lisp-reader-tests.el	Sun Aug 28 10:34:54 2011 +0100
+++ b/tests/automated/lisp-reader-tests.el	Sun Sep 04 19:51:35 2011 +0100
@@ -87,3 +87,66 @@
 	       (read (format "+%d" (1- most-positive-fixnum))))
 	  "checking leading + is handled properly if reading a fixnum"))
 
+;; Test print-circle.
+(let ((cons '#1=(1 2 3 4 5 6 . #1#))
+      (vector #2=[1 2 3 4 5 6 #2#])
+      (compiled-function #3=#[(argument) "\xc2\x09\x08\"\x87"
+                              [pi argument #3#] 3])
+      (char-table #4=#s(char-table :type generic :data (?\u0080 #4#)))
+      (hash-table #5=#s(hash-table :test eql :data (a b c #5# e f)))
+      (range-table #6=#s(range-table :type start-closed-end-open
+                                     :data ((#x00 #xff) hello
+                                            (#x100 #x1ff) #6#
+                                            (#x200 #x2ff) everyone)))
+      (print-readably t)
+      (print-circle t)
+      deserialized-cons deserialized-vector deserialized-compiled-function
+      deserialized-char-table deserialized-hash-table deserialized-range-table)
+  (Assert (eq (nthcdr 6 cons) cons)
+          "checking basic recursive cons read properly")
+  (Assert (eq vector (aref vector (1- (length vector))))
+          "checking basic recursive vector read properly")
+  (Assert (eq compiled-function
+              (find-if #'compiled-function-p
+                       (compiled-function-constants compiled-function)))
+          "checking basic recursive compiled-function read properly")
+  (Check-Error wrong-number-of-arguments (funcall compiled-function 3))
+  (Assert (eq char-table (get-char-table ?\u0080 char-table))
+          "checking basic recursive char table read properly")
+  (Assert (eq hash-table (gethash 'c hash-table))
+          "checking basic recursive hash table read properly")
+  (Assert (eq range-table (get-range-table #x180 range-table))
+          "checking basic recursive range table read properly")
+  (setf (gethash 'g hash-table) cons
+        (car cons) hash-table
+        deserialized-hash-table (read (prin1-to-string hash-table)))
+  (Assert (not (eq deserialized-hash-table hash-table))
+          "checking printing and reading hash-table creates a new object")
+  (Assert (eq deserialized-hash-table (gethash 'c deserialized-hash-table))
+          "checking the lisp reader handles deserialized hash-table identity")
+  (Assert (eq deserialized-hash-table
+              (car (gethash 'g deserialized-hash-table)))
+          "checking the reader handles deserialization identity, hash-table")
+  (setf (get-char-table ?a char-table) cons
+        (car cons) char-table
+        deserialized-char-table (read (prin1-to-string char-table)))
+  (Assert (not (eq deserialized-char-table char-table))
+          "checking printing and reading creates a new object")
+  (Assert (eq deserialized-char-table
+              (get-char-table ?\u0080 deserialized-char-table))
+          "checking the lisp reader handles deserialization identity")
+  (Assert (eq deserialized-char-table
+              (car (get-char-table ?a deserialized-char-table)))
+          "checking the lisp reader handles deserialization identity, mixed")
+  (put-range-table #x1000 #x1010 cons range-table)
+  (setf (car cons) range-table
+        deserialized-range-table (read (prin1-to-string range-table)))
+  (Assert (not (eq deserialized-range-table range-table))
+          "checking printing and reading creates a new object")
+  (Assert (eq deserialized-range-table
+              (get-range-table #x101 deserialized-range-table))
+          "checking the lisp reader handles deserialization identity")
+  (Assert (eq deserialized-range-table
+              (car (get-range-table #x1001 deserialized-range-table)))
+          "checking the lisp reader handles deserialization identity, mixed"))
+