--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/libinterp/corefcn/settings.h	Fri Jun 08 18:04:18 2018 -0400
@@ -0,0 +1,90 @@
+/*
+
+Copyright (C) 2018 John W. Eaton
+
+This file is part of Octave.
+
+Octave 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 3 of the License, or
+(at your option) any later version.
+
+Octave 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 Octave; see the file COPYING.  If not, see
+<https://www.gnu.org/licenses/>.
+
+*/
+
+#if ! defined (octave_settings_h)
+#define octave_settings_h 1
+
+#include "octave-config.h"
+
+class octave_value_list;
+
+namespace octave
+{
+  // Most settings for the interpreter are stored in the classes which
+  // they affect (intput_system, output_system, load_path, etc.  Some
+  // don't really fit anywhere else.  For example, there is no single
+  // lexer or parser object, so we store settings for those things
+  // here.
+
+  class settings
+  {
+  public:
+
+    settings (void);
+
+    settings (const settings&) = delete;
+
+    settings& operator = (const settings&) = delete;
+
+    ~settings (void) = default;
+
+    octave_value display_tokens (const octave_value_list& args, int nargout);
+
+    bool display_tokens (void) const { return m_display_tokens; }
+
+    bool display_tokens (bool flag)
+    {
+      bool val = m_display_tokens;
+      m_display_tokens = flag;
+      return val;
+    }
+
+    // Read only.
+    size_t token_count (void) const { return m_token_count; }
+
+    void increment_token_count (void) { ++m_token_count; }
+
+    octave_value lexer_debug_flag (const octave_value_list& args, int nargout);
+
+    bool lexer_debug_flag (void) const { return m_lexer_debug_flag; }
+
+    bool lexer_debug_flag (bool flag)
+    {
+      bool val = m_lexer_debug_flag;
+      m_lexer_debug_flag = flag;
+      return val;
+    }
+
+  private:
+
+    // Display tokens as they are processed, for debugging.
+    bool m_display_tokens = false;
+
+    // Number of tokens processed since interpreter startup.
+    size_t m_token_count = 0;
+
+    // Internal variable for lexer debugging state.
+    bool m_lexer_debug_flag = false;
+  };
+}
+
+#endif