--- a/src/t-builtins.cc
+++ b/src/t-builtins.cc
@@ -174,10 +174,10 @@
   return os;
 }
 
-tree_constant *
+Octave_object
 builtin_casesen (int argc, char **argv, int nargout)
 {
-  tree_constant *retval = NULL_TREE_CONST;
+  Octave_object retval;
 
   if (argc == 1 || (argc > 1 && strcmp (argv[1], "off") == 0))
     warning ("casesen: sorry, Octave is always case sensitive");
@@ -192,10 +192,10 @@
 /*
  * Change current working directory.
  */
-tree_constant *
+Octave_object
 builtin_cd (int argc, char **argv, int nargout)
 {
-  tree_constant *retval = NULL_TREE_CONST;
+  Octave_object retval;
 
   if (argc > 1)
     {
@@ -251,10 +251,10 @@
  * Wipe out user-defined variables and functions given a list of
  * globbing patterns.
  */
-tree_constant *
+Octave_object
 builtin_clear (int argc, char **argv, int nargout)
 {
-  tree_constant *retval = NULL_TREE_CONST;
+  Octave_object retval;
 
 // Always clear the local table, but don't clear currently compiled
 // functions unless we are at the top level.  (Allowing that to happen
@@ -328,10 +328,10 @@
 /*
  * Associate a cryptic message with a variable name.
  */
-tree_constant *
+Octave_object
 builtin_document (int argc, char **argv, int nargout)
 {
-  tree_constant *retval = NULL_TREE_CONST;
+  Octave_object retval;
   if (argc == 3)
     document_symbol (argv[1], argv[2]);
   else
@@ -342,10 +342,10 @@
 /*
  * Edit commands with your favorite editor.
  */
-tree_constant *
+Octave_object
 builtin_edit_history (int argc, char **argv, int nargout)
 {
-  tree_constant *retval = NULL_TREE_CONST;
+  Octave_object retval;
   do_edit_history (argc, argv);
   return retval;
 }
@@ -353,10 +353,10 @@
 /*
  * Set output format state.
  */
-tree_constant *
+Octave_object
 builtin_format (int argc, char **argv, int nargout)
 {
-  tree_constant *retval = NULL_TREE_CONST;
+  Octave_object retval;
   set_format_style (argc, argv);
   return retval;
 }
@@ -488,10 +488,10 @@
 /*
  * Print cryptic yet witty messages.
  */
-tree_constant *
+Octave_object
 builtin_help (int argc, char **argv, int nargout)
 {
-  tree_constant *retval = NULL_TREE_CONST;
+  Octave_object retval;
 
   if (argc == 1)
     {
@@ -623,10 +623,10 @@
 /*
  * Display, save, or load history.
  */
-tree_constant *
+Octave_object
 builtin_history (int argc, char **argv, int nargout)
 {
-  tree_constant *retval = NULL_TREE_CONST;
+  Octave_object retval;
 
   do_history (argc, argv);
 
@@ -637,10 +637,10 @@
  * Change state flag that determines whether lines are added to plots
  * or drawn on new plots.
  */
-tree_constant *
+Octave_object
 builtin_hold (int argc, char **argv, int nargout)
 {
-  tree_constant *retval = NULL_TREE_CONST;
+  Octave_object retval;
   
   switch (argc)
     {
@@ -809,10 +809,10 @@
  *
  *  -- This function is not terribly robust.
  */
-tree_constant *
+Octave_object
 builtin_load (int argc, char **argv, int nargout)
 {
-  tree_constant *retval = NULL_TREE_CONST;
+  Octave_object retval;
 
   argc--;
   argv++;
@@ -895,10 +895,10 @@
 /*
  * Get a directory listing.
  */
-tree_constant *
+Octave_object
 builtin_ls (int argc, char **argv, int nargout)
 {
-  tree_constant *retval = NULL_TREE_CONST;
+  Octave_object retval;
 
   ostrstream ls_buf;
 
@@ -929,10 +929,10 @@
 /*
  * Run previous commands from the history list.
  */
-tree_constant *
+Octave_object
 builtin_run_history (int argc, char **argv, int nargout)
 {
-  tree_constant *retval = NULL_TREE_CONST;
+  Octave_object retval;
   do_run_history (argc, argv);
   return retval;
 }
@@ -979,10 +979,10 @@
 /*
  * Write variables to an output stream.
  */
-tree_constant *
+Octave_object
 builtin_save (int argc, char **argv, int nargout)
 {
-  tree_constant *retval = NULL_TREE_CONST;
+  Octave_object retval;
 
   if (argc < 2)
     {
@@ -1082,10 +1082,10 @@
 /*
  * Set plotting options.
  */
-tree_constant *
+Octave_object
 builtin_set (int argc, char **argv, int nargout)
 {
-  tree_constant *retval = NULL_TREE_CONST;
+  Octave_object retval;
 
   ostrstream plot_buf;
 
@@ -1113,10 +1113,10 @@
 /*
  * Set plotting options.
  */
-tree_constant *
+Octave_object
 builtin_show (int argc, char **argv, int nargout)
 {
-  tree_constant *retval = NULL_TREE_CONST;
+  Octave_object retval;
 
   ostrstream plot_buf;
 
@@ -1205,10 +1205,10 @@
   return status;
 }
 
-tree_constant *
+Octave_object
 builtin_who (int argc, char **argv, int nargout)
 {
-  tree_constant *retval = NULL_TREE_CONST;
+  Octave_object retval;
 
   int show_builtins = 0;
   int show_functions = (curr_sym_tab == top_level_sym_tab);