////////////////////////////////////////////////////////////////////////
//
// Copyright (C) 2009-2022 The Octave Project Developers
//
// See the file COPYRIGHT.md in the top-level directory of this
// distribution or <https://octave.org/copyright/>.
//
// 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 (HAVE_CONFIG_H)
#  include "config.h"
#endif

#include <cctype>

#include <condition_variable>
#include <iostream>
#include <list>
#include <mutex>
#include <string>
#include <thread>

#include "cmd-edit.h"
#include "file-ops.h"
#include "file-stat.h"
#include "lo-array-errwarn.h"
#include "lo-ieee.h"
#include "oct-env.h"

#include "bp-table.h"
#include "call-stack.h"
#include "cdef-manager.h"
#include "defun.h"
#include "error.h"
#include "errwarn.h"
#include "event-manager.h"
#include "input.h"
#include "interpreter-private.h"
#include "interpreter.h"
#include "mex-private.h"
#include "octave.h"
#include "ov-classdef.h"
#include "ov-fcn-handle.h"
#include "ov-mex-fcn.h"
#include "ov-usr-fcn.h"
#include "ov-re-sparse.h"
#include "ov-cx-sparse.h"
#include "parse.h"
#include "profiler.h"
#include "pt-all.h"
#include "pt-anon-scopes.h"
#include "pt-eval.h"
#include "pt-tm-const.h"
#include "stack-frame.h"
#include "symtab.h"
#include "unwind-prot.h"
#include "utils.h"
#include "variables.h"

OCTAVE_BEGIN_NAMESPACE(octave)

  // Normal evaluator.

  class quit_debug_exception
  {
  public:

    quit_debug_exception (bool all = false) : m_all (all) { }

    quit_debug_exception (const quit_debug_exception&) = default;

    quit_debug_exception& operator = (const quit_debug_exception&) = default;

    ~quit_debug_exception (void) = default;

    bool all (void) const { return m_all; }

  private:

    bool m_all;
  };

  class debugger
  {
  public:

    enum execution_mode
      {
        EX_NORMAL = 0,
        EX_CONTINUE = 1,
        EX_QUIT = 2,
        EX_QUIT_ALL = 3
      };

    debugger (interpreter& interp, std::size_t level)
      : m_interpreter (interp), m_level (level),
        m_execution_mode (EX_NORMAL), m_in_debug_repl (false)
    { }

    int server_loop (void);

    void repl (const std::string& prompt = "debug> ");

    bool in_debug_repl (void) const { return m_in_debug_repl; }

    void dbcont (void) { m_execution_mode = EX_CONTINUE; }

    void dbquit (bool all = false)
    {
      if (all)
        m_execution_mode = EX_QUIT_ALL;
      else
        m_execution_mode = EX_QUIT;
    }

    bool quitting_debugger (void) const;

  private:

    interpreter& m_interpreter;

    std::size_t m_level;
    execution_mode m_execution_mode;
    bool m_in_debug_repl;
  };

  // FIXME: Could the debugger server_loop and repl functions be merged
  // with the corresponding tree_evaluator functions or do they need to
  // remain separate?  They perform nearly the same functions.

  int debugger::server_loop (void)
  {
    // Process events from the event queue.

    tree_evaluator& tw = m_interpreter.get_evaluator ();

    void (tree_evaluator::*server_mode_fptr) (bool)
      = &tree_evaluator::server_mode;
    unwind_action act (server_mode_fptr, &tw, true);

    int exit_status = 0;

    do
      {
        if (m_execution_mode == EX_CONTINUE || tw.dbstep_flag ())
          break;

        if (quitting_debugger ())
          break;

        try
          {
            // FIXME: Should we call octave_quit in the octave::sleep
            // and/or command_editor::run_event_hooks functions?

            octave_quit ();

            // FIXME: Running the event queue should be decoupled from
            // the command_editor.

            // FIXME: Is it OK to use command_editor::run_event_hooks
            // here?  It may run more than one queued function per call,
            // and it seems that the checks at the top of the loop
            // probably need to be done after each individual event
            // function is executed.  For now, maybe the simplest thing
            // would be to pass a predicate function (lambda expression)
            // to the command_editor::run_event_hooks and have it check
            // that and break out of the eval loop(s) if the condition
            // is met?

            // FIXME: We should also use a condition variable to manage
            // the execution of entries in the queue and eliminate the
            // need for the busy-wait loop.

            command_editor::run_event_hooks ();

            release_unreferenced_dynamic_libraries ();

            sleep (0.1);
          }
        catch (const interrupt_exception&)
          {
            octave_interrupt_state = 1;
            m_interpreter.recover_from_exception ();

            // Required newline when the user does Ctrl+C at the prompt.
            if (m_interpreter.interactive ())
              octave_stdout << "\n";
          }
        catch (const index_exception& e)
          {
            m_interpreter.recover_from_exception ();

            std::cerr << "error: unhandled index exception: "
                      << e.message () << " -- trying to return to prompt"
                      << std::endl;
          }
        catch (const execution_exception& ee)
          {
            error_system& es = m_interpreter.get_error_system ();

            es.save_exception (ee);
            es.display_exception (ee);

            if (m_interpreter.interactive ())
              {
                m_interpreter.recover_from_exception ();
              }
            else
              {
                // We should exit with a nonzero status.
                exit_status = 1;
                break;
              }
          }
        catch (const quit_debug_exception& qde)
          {
            if (qde.all ())
              throw;

            // Continue in this debug level.
          }
        catch (const std::bad_alloc&)
          {
            m_interpreter.recover_from_exception ();

            std::cerr << "error: out of memory -- trying to return to prompt"
                      << std::endl;
          }
      }
    while (exit_status == 0);

    if (exit_status == EOF)
      {
        if (m_interpreter.interactive ())
          octave_stdout << "\n";

        exit_status = 0;
      }

    return exit_status;
  }

  void debugger::repl (const std::string& prompt_arg)
  {
    unwind_protect frame;

    frame.protect_var (m_in_debug_repl);
    frame.protect_var (m_execution_mode);

    m_in_debug_repl = true;

    tree_evaluator& tw = m_interpreter.get_evaluator ();

    bool silent = tw.quiet_breakpoint_flag (false);

    frame.add (&tree_evaluator::restore_frame, &tw,
               tw.current_call_stack_frame_number ());

    tw.goto_frame (tw.debug_frame ());

    octave_user_code *caller = tw.current_user_code ();
    std::string fcn_file_nm, fcn_nm;

    if (caller)
      {
        fcn_file_nm = caller->fcn_file_name ();
        fcn_nm = fcn_file_nm.empty () ? caller->name () : fcn_file_nm;
      }

    int curr_debug_line = tw.current_line ();

    std::ostringstream buf;

    input_system& input_sys = m_interpreter.get_input_system ();

    event_manager& evmgr = m_interpreter.get_event_manager ();

    if (! fcn_nm.empty ())
      {
        if (input_sys.gud_mode ())
          {
            static char ctrl_z = 'Z' & 0x1f;

            buf << ctrl_z << ctrl_z << fcn_nm << ':' << curr_debug_line;
          }
        else
          {
            // FIXME: we should come up with a clean way to detect
            // that we are stopped on the no-op command that marks the
            // end of a function or script.

            if (! silent)
              {
                std::shared_ptr<stack_frame> frm = tw.current_user_frame ();

                frm->display_stopped_in_message (buf);
              }

            evmgr.enter_debugger_event (fcn_nm, fcn_file_nm, curr_debug_line);

            evmgr.set_workspace ();

            frame.add (&event_manager::execute_in_debugger_event, &evmgr,
                       fcn_nm, curr_debug_line);

            if (! silent)
              {
                std::string line_buf;

                if (caller)
                  line_buf = caller->get_code_line (curr_debug_line);

                if (! line_buf.empty ())
                  buf << curr_debug_line << ": " << line_buf;
              }
          }
      }

    if (silent)
      command_editor::erase_empty_line (true);

    std::string stopped_in_msg = buf.str ();

    if (m_interpreter.server_mode ())
      {
        if (! stopped_in_msg.empty ())
          octave_stdout << stopped_in_msg << std::endl;

        evmgr.push_event_queue ();

        frame.add (&event_manager::pop_event_queue, &evmgr);

        frame.add (&tree_evaluator::set_parser, &tw, tw.get_parser ());

        std::shared_ptr<push_parser>
          debug_parser (new push_parser (m_interpreter));

        tw.set_parser (debug_parser);

        server_loop ();
      }
    else
      {
        if (! stopped_in_msg.empty ())
          std::cerr << stopped_in_msg << std::endl;

        std::string tmp_prompt = prompt_arg;
        if (m_level > 0)
          tmp_prompt = "[" + std::to_string (m_level) + "]" + prompt_arg;

        frame.add (&input_system::set_PS1, &input_sys, input_sys.PS1 ());
        input_sys.PS1 (tmp_prompt);

        if (! m_interpreter.interactive ())
          {
            void (interpreter::*interactive_fptr) (bool)
              = &interpreter::interactive;
            frame.add (interactive_fptr, &m_interpreter,
                       m_interpreter.interactive ());

            m_interpreter.interactive (true);

            // FIXME: should debugging be possible in an embedded
            // interpreter?

            application *app = application::app ();

            if (app)
              {
                void (application::*forced_interactive_fptr) (bool)
                  = &application::forced_interactive;
                frame.add (forced_interactive_fptr, app,
                           app->forced_interactive ());

                app->forced_interactive (true);
              }
          }

#if defined (OCTAVE_ENABLE_COMMAND_LINE_PUSH_PARSER)

        input_reader reader (m_interpreter);

        push_parser debug_parser (m_interpreter);

#else

        parser debug_parser (m_interpreter);

#endif

        error_system& es = m_interpreter.get_error_system ();

        while (m_in_debug_repl)
          {
            if (m_execution_mode == EX_CONTINUE || tw.dbstep_flag ())
              break;

            if (quitting_debugger ())
              break;

            try
              {
                debug_parser.reset ();

#if defined (OCTAVE_ENABLE_COMMAND_LINE_PUSH_PARSER)

                int retval = 0;

                std::string prompt
                  = command_editor::decode_prompt_string (tmp_prompt);

                do
                  {
                    bool eof = false;
                    std::string input_line = reader.get_input (prompt, eof);

                    if (eof)
                      {
                        retval = EOF;
                        break;
                      }

                    retval = debug_parser.run (input_line, false);

                    prompt = command_editor::decode_prompt_string (input_sys.PS2 ());
                  }
                while (retval < 0);

#else

                int retval = debug_parser.run ();

#endif
                if (command_editor::interrupt (false))
                  {
                    // Break regardless of m_execution_mode value.

                    quitting_debugger ();

                    break;
                  }
                else
                  {
                    if (retval == 0)
                      {
                        std::shared_ptr<tree_statement_list> stmt_list
                          = debug_parser.statement_list ();

                        if (stmt_list)
                          stmt_list->accept (tw);

                        if (octave_completion_matches_called)
                          octave_completion_matches_called = false;

                        // FIXME: the following statement is here because
                        // the last command may have been a dbup, dbdown, or
                        // dbstep command that changed the current debug
                        // frame.  If so, we need to reset the current frame
                        // for the call stack.  But is this right way to do
                        // this job?  What if the statement list was
                        // something like "dbup; dbstack"?  Will the call to
                        // dbstack use the right frame?  If not, how can we
                        // fix this problem?
                        tw.goto_frame (tw.debug_frame ());
                      }

                    octave_quit ();
                  }
              }
            catch (const execution_exception& ee)
              {
                es.save_exception (ee);
                es.display_exception (ee);

                // Ignore errors when in debugging mode;
                m_interpreter.recover_from_exception ();
              }
            catch (const quit_debug_exception& qde)
              {
                if (qde.all ())
                  throw;

                // Continue in this debug level.
              }
          }
      }
  }

  bool debugger::quitting_debugger (void) const
  {
    if (m_execution_mode == EX_QUIT)
      {
        // If there is no enclosing debug level or the top-level
        // repl is not active, handle dbquit the same as dbcont.

        if (m_level > 0 || m_interpreter.server_mode ()
            || m_interpreter.in_top_level_repl ())
          throw quit_debug_exception ();
        else
          return true;
      }

    if (m_execution_mode == EX_QUIT_ALL)
      {
        // If the top-level repl is not active, handle "dbquit all"
        // the same as dbcont.

        if (m_interpreter.server_mode () || m_interpreter.in_top_level_repl ())
          throw quit_debug_exception (true);
        else
          return true;
      }

    return false;
  }

  bool tree_evaluator::at_top_level (void) const
  {
    return m_call_stack.at_top_level ();
  }

  std::string
  tree_evaluator::mfilename (const std::string& opt) const
  {
    std::string fname;

    octave_user_code *fcn = m_call_stack.current_user_code ();

    if (fcn)
      {
        fname = fcn->fcn_file_name ();

        if (fname.empty ())
          fname = fcn->name ();
      }

    if (opt == "fullpathext")
      return fname;

    std::size_t dpos = fname.rfind (sys::file_ops::dir_sep_char ());
    std::size_t epos = fname.rfind ('.');

    if (epos <= dpos+1)
      epos = std::string::npos;

    if (epos != std::string::npos)
      fname = fname.substr (0, epos);

    if (opt == "fullpath")
      return fname;

    if (dpos != std::string::npos)
      fname = fname.substr (dpos+1);

    return fname;
  }

  void tree_evaluator::parse_and_execute (const std::string& input,
                                          bool& incomplete_parse)
  {
    incomplete_parse = false;

    unwind_protect_var<bool> upv (m_in_top_level_repl, true);

    if (at_top_level ())
      {
        dbstep_flag (0);
        reset_debug_state ();
      }

    // FIXME: OK to do this job here, or should it be in the functions
    // that do the actual prompting?

    // Update the time stamp for the "prompt" so that automatically
    // finding modified files based on file modification times will
    // work.  In the future, we may do something completely different to
    // check for changes to files but for now, we rely on the prompt
    // time stamp to limit the checks for file modification times.

    Vlast_prompt_time.stamp ();

    bool eof = false;

    event_manager& evmgr = m_interpreter.get_event_manager ();

    if (command_history::add (input))
      evmgr.append_history (input);

    m_exit_status = m_parser->run (input, eof);

    if (m_exit_status == 0)
      {
        std::shared_ptr<tree_statement_list>
          stmt_list = m_parser->statement_list ();

        if (stmt_list)
          {
            command_editor::increment_current_command_number ();

            eval (stmt_list, m_interpreter.interactive ());

            evmgr.set_workspace ();
          }
        else if (m_parser->at_end_of_input ())
          m_exit_status = EOF;
      }
    else
      incomplete_parse = true;

    // FIXME: Should we be checking m_exit_status or incomplete_parse or
    // both here?  Could EOF have a value other than -1, and is there
    // possible confusion between that state and the parser returning -1?

    if (m_exit_status == -1)
      m_exit_status = 0;
    else
      m_parser->reset ();

    evmgr.pre_input_event ();
  }

  void tree_evaluator::get_line_and_eval (void)
  {
    std::mutex mtx;
    std::unique_lock<std::mutex> lock (mtx);
    std::condition_variable cv;
    bool incomplete_parse = false;
    bool evaluation_pending = false;
    bool exiting = false;

    input_system& input_sys = m_interpreter.get_input_system ();
    event_manager& evmgr = m_interpreter.get_event_manager ();

    while (true)
      {
        // FIXME: Detect EOF?  Use readline?  If
        // so, then we need to disable idle event loop hook function
        // execution.

        std::string ps = incomplete_parse ? input_sys.PS2 () : input_sys.PS1 ();

        std::cout << command_editor::decode_prompt_string (ps);

        std::string input;
        std::getline (std::cin, input);

        if (input.empty ())
          continue;

        incomplete_parse = false;
        evaluation_pending = true;
        exiting = false;

        evmgr.post_event
          ([&] (interpreter& interp)
           {
             // INTERPRETER THREAD

             std::lock_guard<std::mutex> local_lock (mtx);

             try
               {
                 interp.parse_and_execute (input, incomplete_parse);
               }
             catch (const exit_exception&)
               {
                 evaluation_pending = false;
                 exiting = true;
                 cv.notify_all ();
                 throw;
               }
             catch (const execution_exception& ee)
               {
                 error_system& es = m_interpreter.get_error_system ();

                 es.save_exception (ee);
                 es.display_exception (ee);

                 if (m_interpreter.interactive ())
                   {
                     m_interpreter.recover_from_exception ();
                     m_parser->reset ();
                     evaluation_pending = false;
                     cv.notify_all ();
                   }
                 else
                   {
                     evaluation_pending = false;
                     cv.notify_all ();
                     throw exit_exception (1);
                   }
               }
             catch (...)
               {
                 evaluation_pending = false;
                 cv.notify_all ();
                 throw;
               }

             evaluation_pending = false;
             cv.notify_all ();
           });

        // Wait until evaluation is finished before prompting for input
        // again.

        cv.wait (lock, [&] { return ! evaluation_pending; });

        if (exiting)
          break;
      }
  }

  int tree_evaluator::repl (void)
  {
    // The big loop.  Read, Eval, Print, Loop.  Normally user
    // interaction at the command line in a terminal session, but we may
    // also end up here when reading from a pipe or when stdin is
    // connected to a file by the magic of input redirection.

    int exit_status = 0;

    // FIXME: should this choice be a command-line option?  Note that we
    // intend that the push parser interface only be used for
    // interactive sessions.

#if defined (OCTAVE_ENABLE_COMMAND_LINE_PUSH_PARSER)
    static bool use_command_line_push_parser = true;
#else
    static bool use_command_line_push_parser = false;
#endif

    // The following logic is written as it is to allow easy transition
    // to setting USE_COMMAND_LINE_PUSH_PARSER at run time and to
    // simplify the logic of the main loop below by using the same
    // base_parser::run interface for both push and pull parsers.

    std::shared_ptr<base_parser> repl_parser;

    if (m_interpreter.interactive ())
      {
        if (use_command_line_push_parser)
          {
            push_parser *pp
              = new push_parser (m_interpreter,
                                 new input_reader (m_interpreter));

            repl_parser = std::shared_ptr<base_parser> (pp);
          }
        else
          {
            parser *pp = new parser (new lexer (m_interpreter));
            repl_parser = std::shared_ptr<base_parser> (pp);
          }
      }
    else
      {
        parser *pp = new parser (new lexer (stdin, m_interpreter));
        repl_parser = std::shared_ptr<base_parser> (pp);
      }

    do
      {
        try
          {
            unwind_protect_var<bool> upv (m_in_top_level_repl, true);

            repl_parser->reset ();

            if (at_top_level ())
              {
                dbstep_flag (0);
                reset_debug_state ();
              }

            exit_status = repl_parser->run ();

            if (exit_status == 0)
              {
                std::shared_ptr<tree_statement_list>
                  stmt_list = repl_parser->statement_list ();

                if (stmt_list)
                  {
                    command_editor::increment_current_command_number ();

                    eval (stmt_list, m_interpreter.interactive ());
                  }
                else if (repl_parser->at_end_of_input ())
                  {
                    exit_status = EOF;
                    break;
                  }
              }
          }
        catch (const interrupt_exception&)
          {
            m_interpreter.recover_from_exception ();

            // Required newline when the user does Ctrl+C at the prompt.
            if (m_interpreter.interactive ())
              octave_stdout << "\n";
          }
        catch (const index_exception& ie)
          {
            m_interpreter.recover_from_exception ();

            std::cerr << "error: unhandled index exception: "
                      << ie.message () << " -- trying to return to prompt"
                      << std::endl;
          }
        catch (const execution_exception& ee)
          {
            error_system& es = m_interpreter.get_error_system ();

            es.save_exception (ee);
            es.display_exception (ee);

            if (m_interpreter.interactive ())
              m_interpreter.recover_from_exception ();
            else
              {
                // We should exit with a nonzero status.
                exit_status = 1;
                break;
              }
          }
        catch (const quit_debug_exception&)
          {
            m_interpreter.recover_from_exception ();

            // FIXME: Does anything else need to happen here?
          }
        catch (const std::bad_alloc&)
          {
            m_interpreter.recover_from_exception ();

            std::cerr << "error: out of memory -- trying to return to prompt"
                      << std::endl;
          }
      }
    while (exit_status == 0);

    if (exit_status == EOF)
      {
        if (m_interpreter.interactive ())
          octave_stdout << "\n";

        exit_status = 0;
      }

    return exit_status;
  }

  int tree_evaluator::server_loop (void)
  {
    // Process events from the event queue.

    unwind_protect_var<bool> upv1 (m_server_mode, true);

    m_exit_status = 0;

    std::shared_ptr<push_parser> parser (new push_parser (m_interpreter));
    unwind_protect_var<std::shared_ptr<push_parser>> upv2 (m_parser, parser);

    // FIXME: We are currently resetting the parser after every call to
    // recover_from_exception.  This action should probably be handled
    // in a more consistent way, but resetting the parser in every call
    // to interpreter::recover_from_exception appears to cause
    // segfaults in the test suite.

    do
      {
        try
          {
            // FIXME: Should we call octave_quit in the octave::sleep
            // and/or command_editor::run_event_hooks functions?

            octave_quit ();

            // FIXME: Running the event queue should be decoupled from
            // the command_editor.  We should also use a condition
            // variable to manage the execution of entries in the queue
            // and eliminate the need for the busy-wait loop.

            command_editor::run_event_hooks ();

            release_unreferenced_dynamic_libraries ();

            sleep (0.1);
          }
        catch (const interrupt_exception&)
          {
            octave_interrupt_state = 1;
            m_interpreter.recover_from_exception ();
            m_parser->reset ();

            // Required newline when the user does Ctrl+C at the prompt.
            if (m_interpreter.interactive ())
              octave_stdout << "\n";
          }
        catch (const index_exception& e)
          {
            m_interpreter.recover_from_exception ();
            m_parser->reset ();

            std::cerr << "error: unhandled index exception: "
                      << e.message () << " -- trying to return to prompt"
                      << std::endl;
          }
        catch (const execution_exception& ee)
          {
            error_system& es = m_interpreter.get_error_system ();

            es.save_exception (ee);
            es.display_exception (ee);

            if (m_interpreter.interactive ())
              {
                m_interpreter.recover_from_exception ();
                m_parser->reset ();
              }
            else
              {
                // We should exit with a nonzero status.
                m_exit_status = 1;
                break;
              }
          }
        catch (const quit_debug_exception&)
          {
            octave_interrupt_state = 1;
            m_interpreter.recover_from_exception ();
            m_parser->reset ();
          }
        catch (const exit_exception& xe)
          {
            m_exit_status = xe.exit_status ();
            break;
          }
        catch (const std::bad_alloc&)
          {
            m_interpreter.recover_from_exception ();
            m_parser->reset ();

            std::cerr << "error: out of memory -- trying to return to prompt"
                      << std::endl;
          }
      }
    while (m_exit_status == 0);

    if (m_exit_status == EOF)
      {
        if (m_interpreter.interactive ())
          octave_stdout << "\n";

        m_exit_status = 0;
      }

    return m_exit_status;
  }

  void tree_evaluator::eval (std::shared_ptr<tree_statement_list>& stmt_list,
                             bool interactive)
  {
    try
      {
        stmt_list->accept (*this);

        octave_quit ();

        if (! interactive)
          {
            bool quit = (m_returning || m_breaking);

            if (m_returning)
              m_returning = 0;

            if (m_breaking)
              m_breaking--;

            if (quit)
              return;
          }

        if (octave_completion_matches_called)
          octave_completion_matches_called = false;
      }
    catch (const quit_debug_exception&)
      {
        m_interpreter.recover_from_exception ();
      }
  }

  octave_value_list
  tree_evaluator::eval_string (const std::string& eval_str, bool silent,
                               int& parse_status, int nargout)
  {
    octave_value_list retval;

    parser eval_parser (eval_str, m_interpreter);

    do
      {
        eval_parser.reset ();

        // If we are looking at
        //
        //   val = eval ("code");
        //
        // then don't allow code to be parsed as a command.

        if (nargout > 0)
          eval_parser.disallow_command_syntax ();

        parse_status = eval_parser.run ();

        if (parse_status == 0)
          {
            std::shared_ptr<tree_statement_list> stmt_list
              = eval_parser.statement_list ();

            if (stmt_list)
              {
                tree_statement *stmt = nullptr;

                if (stmt_list->length () == 1
                    && (stmt = stmt_list->front ())
                    && stmt->is_expression ())
                  {
                    tree_expression *expr = stmt->expression ();

                    if (silent)
                      expr->set_print_flag (false);

                    retval = expr->evaluate_n (*this, nargout);

                    bool do_bind_ans = false;

                    if (expr->is_identifier ())
                      do_bind_ans = ! is_variable (expr);
                    else
                      do_bind_ans = ! expr->is_assignment_expression ();

                    if (do_bind_ans && ! retval.empty ())
                      bind_ans (retval(0), expr->print_result ());

                    if (nargout == 0)
                      retval = octave_value_list ();
                  }
                else if (nargout == 0)
                  stmt_list->accept (*this);
                else
                  error ("eval: invalid use of statement list");

                if (returning () || breaking () || continuing ())
                  break;
              }
            else if (eval_parser.at_end_of_input ())
              break;
          }
      }
    while (parse_status == 0);

    return retval;
  }

  octave_value tree_evaluator::eval_string (const std::string& eval_str,
                                            bool silent, int& parse_status)
  {
    octave_value retval;

    octave_value_list tmp = eval_string (eval_str, silent, parse_status, 1);

    if (! tmp.empty ())
      retval = tmp(0);

    return retval;
  }

  octave_value_list tree_evaluator::eval_string (const octave_value& arg,
                                                 bool silent, int& parse_status,
                                                 int nargout)
  {
    std::string s = arg.xstring_value ("eval: expecting string argument");

    return eval_string (s, silent, parse_status, nargout);
  }

  octave_value_list tree_evaluator::eval (const std::string& try_code,
                                          int nargout)
  {
    int parse_status = 0;

    return eval_string (try_code, nargout > 0, parse_status, nargout);
  }

  octave_value_list tree_evaluator::eval (const std::string& try_code,
                                          const std::string& catch_code,
                                          int nargout)
  {
    octave_value_list retval;

    error_system& es = m_interpreter.get_error_system ();

    int parse_status = 0;

    bool execution_error = false;

    octave_value_list tmp;

    try
      {
        tmp = eval_string (try_code, nargout > 0, parse_status, nargout);
      }
    catch (const execution_exception& ee)
      {
        es.save_exception (ee);
        m_interpreter.recover_from_exception ();

        execution_error = true;
      }

    if (parse_status != 0 || execution_error)
      {
        tmp = eval_string (catch_code, nargout > 0, parse_status, nargout);

        retval = (nargout > 0) ? tmp : octave_value_list ();
      }
    else
      {
        if (nargout > 0)
          retval = tmp;

        // FIXME: we should really be rethrowing whatever
        // exception occurred, not just throwing an
        // execution exception.
        if (execution_error)
          throw execution_exception ();
      }

    return retval;
  }

  octave_value_list tree_evaluator::evalin (const std::string& context,
                                            const std::string& try_code,
                                            int nargout)
  {
    unwind_action act ([=] (std::size_t frm)
                       {
                         m_call_stack.restore_frame (frm);
                       }, m_call_stack.current_frame ());

    if (context == "caller")
      m_call_stack.goto_caller_frame ();
    else if (context == "base")
      m_call_stack.goto_base_frame ();
    else
      error (R"(evalin: CONTEXT must be "caller" or "base")");

    int parse_status = 0;

    return eval_string (try_code, nargout > 0, parse_status, nargout);
  }

  octave_value_list tree_evaluator::evalin (const std::string& context,
                                            const std::string& try_code,
                                            const std::string& catch_code,
                                            int nargout)
  {
    octave_value_list retval;

    unwind_action act1 ([=] (std::size_t frm)
                        {
                          m_call_stack.restore_frame (frm);
                        }, m_call_stack.current_frame ());

    if (context == "caller")
      m_call_stack.goto_caller_frame ();
    else if (context == "base")
      m_call_stack.goto_base_frame ();
    else
      error (R"(evalin: CONTEXT must be "caller" or "base")");

    error_system& es = m_interpreter.get_error_system ();

    int parse_status = 0;

    bool execution_error = false;

    octave_value_list tmp;

    try
      {
        tmp = eval_string (try_code, nargout > 0, parse_status, nargout);
      }
    catch (const execution_exception& ee)
      {
        es.save_exception (ee);
        m_interpreter.recover_from_exception ();

        execution_error = true;
      }

    if (parse_status != 0 || execution_error)
      {
        tmp = eval_string (catch_code, nargout > 0, parse_status, nargout);

        retval = (nargout > 0) ? tmp : octave_value_list ();
      }
    else
      {
        if (nargout > 0)
          retval = tmp;

        // FIXME: we should really be rethrowing whatever
        // exception occurred, not just throwing an
        // execution exception.
        if (execution_error)
          throw execution_exception ();
      }

    return retval;
  }

  void
  tree_evaluator::visit_anon_fcn_handle (tree_anon_fcn_handle&)
  {
    panic_impossible ();
  }

  void
  tree_evaluator::visit_argument_list (tree_argument_list&)
  {
    panic_impossible ();
  }

  void
  tree_evaluator::visit_arguments_block (tree_arguments_block&)
  {
    warning ("function arguments validation blocks are not supported; INCORRECT RESULTS ARE POSSIBLE");
  }

  void
  tree_evaluator::visit_args_block_attribute_list (tree_args_block_attribute_list&)
  {
    panic_impossible ();
  }

  void
  tree_evaluator::visit_args_block_validation_list (tree_args_block_validation_list&)
  {
    panic_impossible ();
  }

  void
  tree_evaluator::visit_arg_validation (tree_arg_validation&)
  {
    panic_impossible ();
  }

  void
  tree_evaluator::visit_arg_size_spec (tree_arg_size_spec&)
  {
    panic_impossible ();
  }

  void
  tree_evaluator::visit_arg_validation_fcns (tree_arg_validation_fcns&)
  {
    panic_impossible ();
  }

  void
  tree_evaluator::visit_binary_expression (tree_binary_expression&)
  {
    panic_impossible ();
  }

  void
  tree_evaluator::visit_boolean_expression (tree_boolean_expression&)
  {
    panic_impossible ();
  }

  void
  tree_evaluator::visit_compound_binary_expression (tree_compound_binary_expression&)
  {
    panic_impossible ();
  }

  void
  tree_evaluator::visit_break_command (tree_break_command& cmd)
  {
    if (m_echo_state)
      {
        int line = cmd.line ();
        if (line < 0)
          line = 1;
        echo_code (line);
        m_echo_file_pos = line + 1;
      }

    if (m_debug_mode)
      do_breakpoint (cmd.is_active_breakpoint (*this));

    if (m_in_loop_command)
      m_breaking = 1;
    else
      error ("break must appear in a loop in the same file as loop command");
  }

  void
  tree_evaluator::visit_colon_expression (tree_colon_expression&)
  {
    panic_impossible ();
  }

  void
  tree_evaluator::visit_continue_command (tree_continue_command& cmd)
  {
    if (m_echo_state)
      {
        int line = cmd.line ();
        if (line < 0)
          line = 1;
        echo_code (line);
        m_echo_file_pos = line + 1;
      }

    if (m_debug_mode)
      do_breakpoint (cmd.is_active_breakpoint (*this));

    if (m_in_loop_command)
      m_continuing = 1;
  }

  bool
  tree_evaluator::statement_printing_enabled (void)
  {
    return ! (m_silent_functions && (m_statement_context == SC_FUNCTION
                                     || m_statement_context == SC_SCRIPT));
  }

  void
  tree_evaluator::reset_debug_state (void)
  {
    m_debug_mode = (m_bp_table.have_breakpoints ()
                    || m_dbstep_flag != 0
                    || m_break_on_next_stmt
                    || in_debug_repl ());
  }

  void
  tree_evaluator::reset_debug_state (bool mode)
  {
    m_debug_mode = mode;
  }

  void
  tree_evaluator::enter_debugger (const std::string& prompt)
  {
    unwind_protect frame;

    frame.add (command_history::ignore_entries,
               command_history::ignoring_entries ());

    command_history::ignore_entries (false);

    frame.add (&call_stack::restore_frame, &m_call_stack,
               m_call_stack.current_frame ());

    // Don't allow errors or warnings at the debug prompt to push us
    // into deeper levels of debugging.

    error_system& es = m_interpreter.get_error_system ();

    frame.add (&error_system::set_debug_on_error, &es, es.debug_on_error ());

    frame.add (&error_system::set_debug_on_warning, &es,
               es.debug_on_warning ());

    es.debug_on_error (false);
    es.debug_on_warning (false);

    // Go up to the nearest user code frame.

    m_debug_frame = m_call_stack.dbupdown (0);

    // FIXME: probably we just want to print one line, not the
    // entire statement, which might span many lines...
    //
    // tree_print_code tpc (octave_stdout);
    // stmt.accept (tpc);

    debugger *dbgr = new debugger (m_interpreter, m_debugger_stack.size ());

    m_debugger_stack.push (dbgr);

    frame.add ([=] (void)
               {
                 delete m_debugger_stack.top ();
                 m_debugger_stack.pop ();
                 reset_debug_state ();
               });

    dbgr->repl (prompt);
  }

  void
  tree_evaluator::keyboard (const std::string& prompt)
  {
    enter_debugger (prompt);
  }

  void
  tree_evaluator::dbupdown (int n, bool verbose)
  {
    m_debug_frame = m_call_stack.dbupdown (n, verbose);
  }

  Matrix
  tree_evaluator::ignored_fcn_outputs (void) const
  {
    Matrix retval;

    const std::list<octave_lvalue> *lvalues = m_lvalue_list;

    if (! lvalues)
      return retval;

    octave_idx_type nbh = 0;

    for (const auto& lval : *lvalues)
      nbh += lval.is_black_hole ();

    if (nbh > 0)
      {
        retval.resize (1, nbh);

        octave_idx_type k = 0;
        octave_idx_type l = 0;

        for (const auto& lval : *lvalues)
          {
            if (lval.is_black_hole ())
              retval(l++) = k+1;

            k += lval.numel ();
          }
      }

    return retval;
  }

  // If NAME is an operator (like "+", "-", ...), convert it to the
  // corresponding function name ("plus", "minus", ...).

  static std::string
  get_operator_function_name (const std::string& name)
  {
    // Bow to the god of compatibility.

    // FIXME: it seems ugly to put this here, but there is no single
    // function in the parser that converts from the operator name to
    // the corresponding function name.  At least try to do it without N
    // string compares.

    // FIXME: .+, .-, **, and .** are deprecated but still need to be
    // handled here until they are removed.

    std::size_t len = name.length ();

    if (len == 3 && name == ".**")
      // deprecated
      return "power";
    else if (len == 2)
      {
        if (name[0] == '.')
          {
            switch (name[1])
              {
              case '\'':
                return "transpose";

              case '+':
                // deprecated
                return "plus";

              case '-':
                // deprecated
                return "minus";

              case '*':
                return "times";

              case '/':
                return "rdivide";

              case '^':
                return "power";

              case '\\':
                return "ldivide";

              default:
                break;
              }
          }
        else if (name[1] == '=')
          {
            switch (name[0])
              {
              case '<':
                return "le";

              case '=':
                return "eq";

              case '>':
                return "ge";

              case '~':
              case '!':
                return "ne";

              default:
                break;
              }
          }
        else if (name == "**")
          // deprecated
          return "mpower";
      }
    else if (len == 1)
      {
        switch (name[0])
          {
          case '~':
          case '!':
            return "not";

          case '\'':
            return "ctranspose";

          case '+':
            return "plus";

          case '-':
            return "minus";

          case '*':
            return "mtimes";

          case '/':
            return "mrdivide";

          case '^':
            return "mpower";

          case '\\':
            return "mldivide";

          case '<':
            return "lt";

          case '>':
            return "gt";

          case '&':
            return "and";

          case '|':
            return "or";

          default:
            break;
          }
      }

    return name;
  }

  // Creates a function handle that takes into account the context,
  // finding local, nested, private, or sub functions.

  octave_value
  tree_evaluator::make_fcn_handle (const std::string& name)
  {
    octave_value retval;

    // The str2func function can create a function handle with the name
    // of an operator (for example, "+").  If so, it is converted to the
    // name of the corresponding function ("+" -> "plus") and we create
    // a simple function handle using that name.

    std::string fcn_name = get_operator_function_name (name);

    // If FCN_NAME is different from NAME, then NAME is an operator.  As
    // of version 2020a, Matlab apparently uses the function name
    // corresponding to the operator to search for private and local
    // functions in the current scope but not(!) nested functions.

    bool name_is_operator = fcn_name != name;

    std::size_t pos = fcn_name.find ('.');

    if (pos != std::string::npos)
      {
        // Recognize (some of?  which ones?) the following cases
        // and create something other than a simple function handle?
        // Should we just be checking for the last two when the first
        // element of the dot-separated list is an object?  If so, then
        // should this syntax be limited to a dot-separated list with
        // exactly two elements?
        //
        //   object . method
        //   object . static-method
        //
        // Code to do that duplicates some of simple_fcn_handle::call.

        // Only accept expressions that contain one '.' separator.

        // FIXME: The logic here is a bit complicated.  Is there a good
        // way to simplify it?

        std::string meth_nm = fcn_name.substr (pos+1);

        if (meth_nm.find ('.') == std::string::npos)
          {
            std::string obj_nm = fcn_name.substr (0, pos);

            // If obj_nm is an object in the current scope with a
            // method named meth_nm, create a classsimple handle.

            octave_value object = varval (obj_nm);

            if (object.is_defined () && object.is_classdef_object ())
              {
                octave_classdef *cdef = object.classdef_object_value ();

                if (cdef)
                  {
                    std::string class_nm = cdef->class_name ();

                    cdef_object cdef_obj = cdef->get_object ();

                    cdef_class cls = cdef_obj.get_class ();

                    cdef_method meth = cls.find_method (meth_nm);

                    if (meth.ok ())
                      {
                        // If the method we found is static, create a
                        // new function name from the class name and
                        // method name and create a simple function
                        // handle below.  Otherwise, create a class
                        // simple function handle.

                        if (meth.is_static ())
                          fcn_name = class_nm + '.' + meth_nm;
                        else
                          {
                            octave_value meth_fcn = meth.get_function ();

                            octave_fcn_handle *fh
                              = new octave_fcn_handle (object, meth_fcn,
                                                       class_nm, meth_nm);

                            return octave_value (fh);
                          }
                      }
                  }
              }
          }

        // We didn't match anything above, so create handle to SIMPLE
        // package function or static class method.  Function resolution
        // is performed when the handle is used.

        return octave_value (new octave_fcn_handle (fcn_name));
      }

    // If the function name refers to a sub/local/private function or a
    // class method/constructor, create scoped function handle that is
    // bound to that function.  Use the same precedence list as
    // fcn_info::find but limit search to the following types of
    // functions:
    //
    //   nested functions (and subfunctions)
    //   local functions in the current file
    //   private function
    //   class method
    //
    // For anything else we create a simple function handle that will be
    // resolved dynamically in the scope where it is evaluated.

    symbol_scope curr_scope = get_current_scope ();

    symbol_table& symtab = m_interpreter.get_symbol_table ();

    if (curr_scope)
      {
        octave_value ov_fcn
          = symtab.find_scoped_function (fcn_name, curr_scope);

        // If name is operator, we are in Fstr2func, so skip the stack
        // frame for that function.

        bool skip_first = name_is_operator;
        octave_function *curr_fcn = current_function (skip_first);

        if (ov_fcn.is_defined ())
          {
            octave_function *fcn = ov_fcn.function_value ();

            if (fcn->is_nested_function ())
              {
                if (! name_is_operator)
                  {
                    // Get current stack frame and return handle to nested
                    // function.

                    std::shared_ptr<stack_frame> frame
                      = m_call_stack.get_current_stack_frame ();

                    // If we are creating a handle to the current
                    // function or a handle to a sibling function (i.e.,
                    // not a child of the current function), then use
                    // the calling stack frame as the context instead of
                    // the current stack frame.

                    // FIXME:  Do we need both checks here or is it
                    // sufficient to check that the parent of curr_fcn
                    // is the same as the parent of fcn?  Is there any
                    // case where curr_fcn could be nullptr, or does
                    // that indicate an internal error of some kind?

                    if (curr_fcn
                        && (fcn_name == curr_fcn->name ()
                            || fcn->parent_fcn_name () == curr_fcn->parent_fcn_name ()))
                      frame = frame->access_link ();

                    octave_fcn_handle *fh
                      = new octave_fcn_handle (ov_fcn, fcn_name, frame);

                    return octave_value (fh);
                  }
              }
            else if (fcn->is_subfunction ()
                     /* || fcn->is_localfunction () */
                     || fcn->is_private_function ())
              {
                // Create handle to SCOPED function (sub/local function
                // or private function).

                std::list<std::string> parentage = fcn->parent_fcn_names ();

                octave_fcn_handle *fh
                  = new octave_fcn_handle (ov_fcn, fcn_name, parentage);

                return octave_value (fh);
              }
          }

        if (curr_fcn && (curr_fcn->is_class_method ()
                         || curr_fcn->is_class_constructor ()))
          {
            std::string dispatch_class = curr_fcn->dispatch_class ();

            octave_value ov_meth
              = symtab.find_method (fcn_name, dispatch_class);

            if (ov_meth.is_defined ())
              {
                octave_function *fcn = ov_meth.function_value ();

                // FIXME: do we need to check that it is a method of
                // dispatch_class, or is it sufficient to just check
                // that it is a method?

                if (fcn->is_class_method ())
                  {
                    // Create CLASSSIMPLE handle to method but don't
                    // bind to the method.  Lookup will be done later.

                    octave_fcn_handle *fh
                      = new octave_fcn_handle (dispatch_class, fcn_name);

                    return octave_value (fh);
                  }
              }
          }
      }

    octave_value ov_fcn = symtab.find_user_function (fcn_name);

    // Create handle to SIMPLE function.  If the function is not found
    // now, then we will look for it again when the handle is used.

    return octave_value (new octave_fcn_handle (ov_fcn, fcn_name));
  }

/*
%!test
%! x = {".**", "power";
%!      ".'", "transpose";
%!      ".+", "plus";
%!      ".-", "minus";
%!      ".*", "times";
%!      "./", "rdivide";
%!      ".^", "power";
%!      ".\\", "ldivide";
%!      "<=", "le";
%!      "==", "eq";
%!      ">=", "ge";
%!      "!=", "ne";
%!      "~=", "ne";
%!      "**", "mpower";
%!      "~", "not";
%!      "!", "not";
%!      "\'", "ctranspose";
%!      "+", "plus";
%!      "-", "minus";
%!      "*", "mtimes";
%!      "/", "mrdivide";
%!      "^", "mpower";
%!      "\\", "mldivide";
%!      "<", "lt";
%!      ">", "gt";
%!      "&", "and";
%!      "|", "or"};
%! for i = 1:rows (x)
%!   assert (functions (str2func (x{i,1})).function, x{i,2});
%! endfor
*/

  octave_value
  tree_evaluator::evaluate (tree_decl_elt *elt)
  {
    // Do not allow functions to return null values.

    tree_identifier *id = elt->ident ();

    return id ? id->evaluate (*this).storable_value () : octave_value ();
  }

  bool
  tree_evaluator::is_variable (const std::string& name) const
  {
    std::shared_ptr<stack_frame> frame
      = m_call_stack.get_current_stack_frame ();

    return frame->is_variable (name);
  }

  bool
  tree_evaluator::is_local_variable (const std::string& name) const
  {
    std::shared_ptr<stack_frame> frame
      = m_call_stack.get_current_stack_frame ();

    return frame->is_local_variable (name);
  }

  bool
  tree_evaluator::is_variable (const tree_expression *expr) const
  {
    if (expr->is_identifier ())
      {
        const tree_identifier *id
          = dynamic_cast<const tree_identifier *> (expr);

        if (id->is_black_hole ())
          return false;

        return is_variable (id->symbol ());
      }

    return false;
  }

  bool
  tree_evaluator::is_defined (const tree_expression *expr) const
  {
    if (expr->is_identifier ())
      {
        const tree_identifier *id
          = dynamic_cast<const tree_identifier *> (expr);

        return is_defined (id->symbol ());
      }

    return false;
  }

  bool
  tree_evaluator::is_variable (const symbol_record& sym) const
  {
    std::shared_ptr<stack_frame> frame
      = m_call_stack.get_current_stack_frame ();

    return frame->is_variable (sym);
  }

  bool
  tree_evaluator::is_defined (const symbol_record& sym) const
  {
    std::shared_ptr<stack_frame> frame
      = m_call_stack.get_current_stack_frame ();

    return frame->is_defined (sym);
  }

  bool tree_evaluator::is_global (const std::string& name) const
  {
    std::shared_ptr<stack_frame> frame
      = m_call_stack.get_current_stack_frame ();

    return frame->is_global (name);
  }

  octave_value
  tree_evaluator::varval (const symbol_record& sym) const
  {
    std::shared_ptr<stack_frame> frame
      = m_call_stack.get_current_stack_frame ();

    return frame->varval (sym);
  }

  octave_value
  tree_evaluator::varval (const std::string& name) const
  {
    std::shared_ptr<stack_frame> frame
      = m_call_stack.get_current_stack_frame ();

    return frame->varval (name);
  }

  void tree_evaluator::install_variable (const std::string& name,
                                         const octave_value& value,
                                         bool global)
  {
    std::shared_ptr<stack_frame> frame
      = m_call_stack.get_current_stack_frame ();

    return frame->install_variable (name, value, global);
  }

  octave_value
  tree_evaluator::global_varval (const std::string& name) const
  {
    return m_call_stack.global_varval (name);
  }

  octave_value&
  tree_evaluator::global_varref (const std::string& name)
  {
    return m_call_stack.global_varref (name);
  }

  void
  tree_evaluator::global_assign (const std::string& name,
                                 const octave_value& val)
  {
    m_call_stack.global_varref (name) = val;
  }

  octave_value
  tree_evaluator::top_level_varval (const std::string& name) const
  {
    return m_call_stack.get_top_level_value (name);
  }

  void
  tree_evaluator::top_level_assign (const std::string& name,
                                    const octave_value& val)
  {
    m_call_stack.set_top_level_value (name, val);
  }

  void
  tree_evaluator::assign (const std::string& name, const octave_value& val)
  {
    std::shared_ptr<stack_frame> frame
      = m_call_stack.get_current_stack_frame ();

    frame->assign (name, val);
  }

  void
  tree_evaluator::assignin (const std::string& context,
                            const std::string& name, const octave_value& val)
  {
    // FIXME: Can this be done without an unwind-protect frame, simply
    // by getting a reference to the caller or base stack frame and
    // calling assign on that?

    unwind_action act ([=] (std::size_t frm)
                       {
                         m_call_stack.restore_frame (frm);
                       }, m_call_stack.current_frame ());

    if (context == "caller")
      m_call_stack.goto_caller_frame ();
    else if (context == "base")
      m_call_stack.goto_base_frame ();
    else
      error (R"(assignin: CONTEXT must be "caller" or "base")");

    if (valid_identifier (name))
      {
        // Put the check here so that we don't slow down assignments
        // generally.  Any that go through Octave's parser should have
        // already been checked.

        if (iskeyword (name))
          error ("assignin: invalid assignment to keyword '%s'",
                 name.c_str ());

        assign (name, val);
      }
    else
      error ("assignin: invalid variable name '%s'", name.c_str ());
  }

  void
  tree_evaluator::source_file (const std::string& file_name,
                               const std::string& context,
                               bool verbose, bool require_file)
  {
    // Map from absolute name of script file to recursion level.  We
    // use a map instead of simply placing a limit on recursion in the
    // source_file function so that two mutually recursive scripts
    // written as
    //
    //   foo1.m:
    //   ------
    //   foo2
    //
    //   foo2.m:
    //   ------
    //   foo1
    //
    // and called with
    //
    //   foo1
    //
    // (for example) will behave the same if they are written as
    //
    //   foo1.m:
    //   ------
    //   source ("foo2.m")
    //
    //   foo2.m:
    //   ------
    //   source ("foo1.m")
    //
    // and called with
    //
    //   source ("foo1.m")
    //
    // (for example).

    static std::map<std::string, int> source_call_depth;

    std::string file_full_name
      = sys::file_ops::tilde_expand (file_name);

    std::size_t pos
      = file_full_name.find_last_of (sys::file_ops::dir_sep_str ());

    std::string dir_name = file_full_name.substr (0, pos);

    file_full_name = sys::env::make_absolute (file_full_name);

    unwind_protect frame;

    if (source_call_depth.find (file_full_name) == source_call_depth.end ())
      source_call_depth[file_full_name] = -1;

    frame.protect_var (source_call_depth[file_full_name]);

    source_call_depth[file_full_name]++;

    if (source_call_depth[file_full_name] >= max_recursion_depth ())
      error ("max_recursion_depth exceeded");

    if (! context.empty ())
      {
        frame.add (&call_stack::restore_frame, &m_call_stack,
                   m_call_stack.current_frame ());

        if (context == "caller")
          m_call_stack.goto_caller_frame ();
        else if (context == "base")
          m_call_stack.goto_base_frame ();
        else
          error (R"(source: CONTEXT must be "caller" or "base")");
      }

    // Find symbol name that would be in symbol_table, if it were loaded.
    std::size_t dir_end
      = file_name.find_last_of (sys::file_ops::dir_sep_chars ());
    dir_end = (dir_end == std::string::npos) ? 0 : dir_end + 1;

    std::size_t extension = file_name.find_last_of ('.');
    if (extension == std::string::npos)
      extension = file_name.length ();

    std::string symbol = file_name.substr (dir_end, extension - dir_end);
    std::string full_name = sys::canonicalize_file_name (file_name);

    // Check if this file is already loaded (or in the path)
    symbol_table& symtab = m_interpreter.get_symbol_table ();
    octave_value ov_code = symtab.fcn_table_find (symbol);

    // For compatibility with Matlab, accept both scripts and
    // functions.

    if (ov_code.is_user_code ())
      {
        octave_user_code *code = ov_code.user_code_value ();

        if (! code
            || (sys::canonicalize_file_name (code->fcn_file_name ())
                != full_name))
          {
            // Wrong file, so load it below.
            ov_code = octave_value ();
          }
      }
    else
      {
        // Not a script, so load it below.
        ov_code = octave_value ();
      }

    // If no symbol of this name, or the symbol is for a different
    // file, load.

    if (ov_code.is_undefined ())
      {
        try
          {
            ov_code = parse_fcn_file (m_interpreter, file_full_name,
                                      file_name, dir_name, "", "",
                                      require_file, true, false, false);
          }
        catch (execution_exception& ee)
          {
            error (ee, "source: error sourcing file '%s'",
                   file_full_name.c_str ());
          }
      }

    // Return or error if we don't have a valid script or function.

    if (ov_code.is_undefined ())
      return;

    if (! ov_code.is_user_code ())
      error ("source: %s is not a script", full_name.c_str ());

    if (verbose)
      {
        octave_stdout << "executing commands from " << full_name << " ... ";
        octave_stdout.flush ();
      }

    octave_user_code *code = ov_code.user_code_value ();

    code->call (*this, 0, octave_value_list ());

    if (verbose)
      octave_stdout << "done." << std::endl;
  }

  void
  tree_evaluator::set_auto_fcn_var (stack_frame::auto_var_type avt,
                                    const octave_value& val)
  {
    m_call_stack.set_auto_fcn_var (avt, val);
  }

  octave_value
  tree_evaluator::get_auto_fcn_var (stack_frame::auto_var_type avt) const
  {
    return m_call_stack.get_auto_fcn_var (avt);
  }

  void
  tree_evaluator::define_parameter_list_from_arg_vector
    (tree_parameter_list *param_list, const octave_value_list& args)
  {
    if (! param_list || param_list->varargs_only ())
      return;

    int i = -1;

    for (tree_decl_elt *elt : *param_list)
      {
        i++;

        octave_lvalue ref = elt->lvalue (*this);

        if (i < args.length ())
          {
            if (args(i).is_defined () && args(i).is_magic_colon ())
              {
                if (! eval_decl_elt (elt))
                  error ("no default value for argument %d", i+1);
              }
            else
              ref.define (args(i));
          }
        else
          eval_decl_elt (elt);
      }
  }

  void
  tree_evaluator::undefine_parameter_list (tree_parameter_list *param_list)
  {
    for (tree_decl_elt *elt : *param_list)
      {
        octave_lvalue ref = elt->lvalue (*this);

        ref.assign (octave_value::op_asn_eq, octave_value ());
      }
  }

// END is documented in op-kw-docs.
DEFMETHOD (end, interp, args, ,
           doc: /* -*- texinfo -*-
@deftypefn {} {} end
Last element of an array or the end of any @code{for}, @code{parfor},
@code{if}, @code{do}, @code{while}, @code{function}, @code{switch},
@code{try}, or @code{unwind_protect} block.

As an index of an array, the magic index @qcode{"end"} refers to the
last valid entry in an indexing operation.

Example:

@example
@group
@var{x} = [ 1 2 3; 4 5 6 ];
@var{x}(1,end)
   @result{} 3
@var{x}(end,1)
   @result{} 4
@var{x}(end,end)
   @result{} 6
@end group
@end example
@seealso{for, parfor, if, do, while, function, switch, try, unwind_protect}
@end deftypefn */)
{
  tree_evaluator& tw = interp.get_evaluator ();

  return tw.evaluate_end_expression (args);
}

/*
%!test <*58830>
%! fail ("__undef_sym__ (end)",
%!       "invalid use of 'end': may only be used to index existing value");

%!test <*58953>
%! x = 1:10;
%! assert (x(end), 10);
%! assert (x(minus (end, 1)), 9);
%! assert (x(minus (minus (end, 1), 1)), 8);
*/

  octave_value_list
  tree_evaluator::convert_to_const_vector (tree_argument_list *args)
  {
    std::list<octave_value> arg_vals;

    for (auto elt : *args)
      {
        // FIXME: is it possible for elt to be invalid?

        if (! elt)
          break;

        octave_value tmp = elt->evaluate (*this);

        if (tmp.is_cs_list ())
          {
            octave_value_list tmp_ovl = tmp.list_value ();

            for (octave_idx_type i = 0; i < tmp_ovl.length (); i++)
              arg_vals.push_back (tmp_ovl(i));
          }
        else if (tmp.is_defined ())
          arg_vals.push_back (tmp);
      }

    return octave_value_list (arg_vals);
  }

  octave_value_list
  tree_evaluator::convert_return_list_to_const_vector
    (tree_parameter_list *ret_list, int nargout, const Matrix& ignored_outputs,
     const Cell& varargout)
  {
    octave_idx_type vlen = varargout.numel ();
    int len = ret_list->length ();

    // Special case.  Will do a shallow copy.
    if (len == 0)
      return varargout;
    else
      {
        int i = 0;
        int k = 0;
        int num_ignored = ignored_outputs.numel ();
        int ignored = num_ignored > 0 ? ignored_outputs(k) - 1 : -1;

        if (nargout <= len)
          {
            int nout = nargout > 0 ? nargout : 1;
            octave_value_list retval (nout);

            for (tree_decl_elt *elt : *ret_list)
              {
                if (nargout == 0 && ! is_defined (elt->ident ()))
                  break;

                if (ignored >= 0 && i == ignored)
                  {
                    i++;
                    k++;
                    ignored = k < num_ignored ? ignored_outputs(k) - 1 : -1;
                  }
                else
                  retval(i++) = evaluate (elt);

                if (i == nout)
                  break;
              }

            return retval;
          }
        else
          {
            octave_value_list retval (len + vlen);

            for (tree_decl_elt *elt : *ret_list)
              {
                if (ignored >= 0 && i == ignored)
                  {
                    i++;
                    k++;
                    ignored = k < num_ignored ? ignored_outputs(k) - 1 : -1;
                  }
                else
                  retval(i++) = evaluate (elt);
              }

            for (octave_idx_type j = 0; j < vlen; j++)
              retval(i++) = varargout(j);

            return retval;
          }
      }
  }

  bool
  tree_evaluator::eval_decl_elt (tree_decl_elt *elt)
  {
    bool retval = false;

    tree_identifier *id = elt->ident ();
    tree_expression *expr = elt->expression ();

    if (id && expr)
      {
        octave_lvalue ult = id->lvalue (*this);

        octave_value init_val = expr->evaluate (*this);

        ult.assign (octave_value::op_asn_eq, init_val);

        retval = true;
      }

    return retval;
  }

  bool
  tree_evaluator::switch_case_label_matches (tree_switch_case *expr,
                                             const octave_value& val)
  {
    tree_expression *label = expr->case_label ();

    octave_value label_value = label->evaluate (*this);

    if (label_value.is_defined ())
      {
        if (label_value.iscell ())
          {
            Cell cell (label_value.cell_value ());

            for (octave_idx_type i = 0; i < cell.rows (); i++)
              {
                for (octave_idx_type j = 0; j < cell.columns (); j++)
                  {
                    bool match = val.is_equal (cell(i,j));

                    if (match)
                      return true;
                  }
              }
          }
        else
          return val.is_equal (label_value);
      }

    return false;
  }

  void tree_evaluator::push_stack_frame (const symbol_scope& scope)
  {
    m_call_stack.push (scope);
  }

  void tree_evaluator::push_stack_frame (octave_user_function *fcn,
                                         const std::shared_ptr<stack_frame>& closure_frames)
  {
    m_call_stack.push (fcn, closure_frames);
  }

  void tree_evaluator::push_stack_frame (octave_user_function *fcn,
                                         const stack_frame::local_vars_map& local_vars,
                                         const std::shared_ptr<stack_frame>& closure_frames)
  {
    m_call_stack.push (fcn, local_vars, closure_frames);
  }

  void tree_evaluator::push_stack_frame (octave_user_script *script)
  {
    m_call_stack.push (script);
  }

  void tree_evaluator::push_stack_frame (octave_function *fcn)
  {
    m_call_stack.push (fcn);
  }

  void tree_evaluator::pop_stack_frame (void)
  {
    m_call_stack.pop ();
  }

  int tree_evaluator::current_line (void) const
  {
    return m_call_stack.current_line ();
  }

  int tree_evaluator::current_column (void) const
  {
    return m_call_stack.current_column ();
  }

  int tree_evaluator::debug_user_code_line (void) const
  {
    return m_call_stack.debug_user_code_line ();
  }

  int tree_evaluator::debug_user_code_column (void) const
  {
    return m_call_stack.debug_user_code_column ();
  }

  void tree_evaluator::debug_where (std::ostream& os) const
  {
    std::shared_ptr<stack_frame> frm = m_call_stack.current_user_frame ();

    frm->display_stopped_in_message (os);
  }

  octave_user_code * tree_evaluator::current_user_code (void) const
  {
    return m_call_stack.current_user_code ();
  }

  unwind_protect * tree_evaluator::curr_fcn_unwind_protect_frame (void)
  {
    return m_call_stack.curr_fcn_unwind_protect_frame ();
  }

  octave_user_code * tree_evaluator::debug_user_code (void) const
  {
    return m_call_stack.debug_user_code ();
  }

  octave_function * tree_evaluator::current_function (bool skip_first) const
  {
    return m_call_stack.current_function (skip_first);
  }

  octave_function * tree_evaluator::caller_function (void) const
  {
    return m_call_stack.current_function (true);
  }

  bool tree_evaluator::goto_frame (std::size_t n, bool verbose)
  {
    return m_call_stack.goto_frame (n, verbose);
  }

  void tree_evaluator::goto_caller_frame (void)
  {
    m_call_stack.goto_caller_frame ();
  }

  void tree_evaluator::goto_base_frame (void)
  {
    m_call_stack.goto_base_frame ();
  }

  void tree_evaluator::restore_frame (std::size_t n)
  {
    return m_call_stack.restore_frame (n);
  }

  std::string tree_evaluator::get_dispatch_class (void) const
  {
    return m_call_stack.get_dispatch_class ();
  }

  void tree_evaluator::set_dispatch_class (const std::string& class_name)
  {
    m_call_stack.set_dispatch_class (class_name);
  }

  bool
  tree_evaluator::is_class_method_executing (std::string& dclass) const
  {
    return m_call_stack.is_class_method_executing (dclass);
  }

  bool
  tree_evaluator::is_class_constructor_executing (std::string& dclass) const
  {
    return m_call_stack.is_class_constructor_executing (dclass);
  }

  std::list<std::shared_ptr<stack_frame>>
  tree_evaluator::backtrace_frames (octave_idx_type& curr_user_frame) const
  {
    return m_call_stack.backtrace_frames (curr_user_frame);
  }

  std::list<std::shared_ptr<stack_frame>>
  tree_evaluator::backtrace_frames (void) const
  {
    return m_call_stack.backtrace_frames ();
  }

  std::list<frame_info>
  tree_evaluator::backtrace_info (octave_idx_type& curr_user_frame,
                                  bool print_subfn) const
  {
    return m_call_stack.backtrace_info (curr_user_frame, print_subfn);
  }

  std::list<frame_info> tree_evaluator::backtrace_info (void) const
  {
    return m_call_stack.backtrace_info ();
  }

  octave_map
  tree_evaluator::backtrace (octave_idx_type& curr_user_frame,
                             bool print_subfn) const
  {
    return m_call_stack.backtrace (curr_user_frame, print_subfn);
  }

  octave_map tree_evaluator::backtrace (void) const
  {
    return m_call_stack.backtrace ();
  }

  octave_map tree_evaluator::empty_backtrace (void) const
  {
    return m_call_stack.empty_backtrace ();
  }

  std::string tree_evaluator::backtrace_message (void) const
  {
    std::list<frame_info> frames = backtrace_info ();

    std::ostringstream buf;

    for (const auto& frm : frames)
      {
        buf << "    " << frm.fcn_name ();

        int line = frm.line ();

        if (line > 0)
          {
            buf << " at line " << line;

            int column = frm.column ();

            if (column > 0)
              buf << " column " << column;

            buf << "\n";
          }
      }

    return buf.str ();
  }

  void tree_evaluator::push_dummy_scope (const std::string& name)
  {
    symbol_scope dummy_scope (name + "$dummy");

    m_call_stack.push (dummy_scope);
  }

  void tree_evaluator::pop_scope (void)
  {
    m_call_stack.pop ();
  }

  symbol_scope tree_evaluator::get_top_scope (void) const
  {
    return m_call_stack.top_scope ();
  }

  symbol_scope tree_evaluator::get_current_scope (void) const
  {
    return m_call_stack.current_scope ();
  }

  void tree_evaluator::mlock (bool skip_first) const
  {
    octave_function *fcn = m_call_stack.current_function (skip_first);

    if (! fcn)
      error ("mlock: invalid use outside a function");

    if (fcn->is_builtin_function ())
      {
        warning ("mlock: locking built-in function has no effect");
        return;
      }

    fcn->lock ();
  }

  void tree_evaluator::munlock (bool skip_first) const
  {
    octave_function *fcn = m_call_stack.current_function (skip_first);

    if (! fcn)
      error ("munlock: invalid use outside a function");

    if (fcn->is_builtin_function ())
      {
        warning ("munlock: unlocking built-in function has no effect");
        return;
      }

    fcn->unlock ();
  }

  bool tree_evaluator::mislocked (bool skip_first) const
  {
    octave_function *fcn = m_call_stack.current_function (skip_first);

    if (! fcn)
      error ("mislocked: invalid use outside a function");

    return fcn->islocked ();
  }

  octave_value
  tree_evaluator::max_stack_depth (const octave_value_list& args, int nargout)
  {
    return m_call_stack.max_stack_depth (args, nargout);
  }

  void tree_evaluator::display_call_stack (void) const
  {
    m_call_stack.display ();
  }

  octave_value tree_evaluator::find (const std::string& name)
  {
    std::shared_ptr<stack_frame> frame
      = m_call_stack.get_current_stack_frame ();

    octave_value val = frame->varval (name);

    if (val.is_defined ())
      return val;

    // Subfunction.  I think it only makes sense to check for
    // subfunctions if we are currently executing a function defined
    // from a .m file.

    octave_value fcn = frame->find_subfunction (name);

    if (fcn.is_defined ())
      return fcn;

    symbol_table& symtab = m_interpreter.get_symbol_table ();

    return symtab.fcn_table_find (name, ovl ());
  }

  void tree_evaluator::clear_objects (void)
  {
    std::shared_ptr<stack_frame> frame
      = m_call_stack.get_current_stack_frame ();

    frame->clear_objects ();
  }

  void tree_evaluator::clear_variable (const std::string& name)
  {
    std::shared_ptr<stack_frame> frame
      = m_call_stack.get_current_stack_frame ();

    frame->clear_variable (name);
  }

  void tree_evaluator::clear_variable_pattern (const std::string& pattern)
  {
    std::shared_ptr<stack_frame> frame
      = m_call_stack.get_current_stack_frame ();

    frame->clear_variable_pattern (pattern);
  }

  void tree_evaluator::clear_variable_regexp (const std::string& pattern)
  {
    std::shared_ptr<stack_frame> frame
      = m_call_stack.get_current_stack_frame ();

    frame->clear_variable_regexp (pattern);
  }

  void tree_evaluator::clear_variables (void)
  {
    std::shared_ptr<stack_frame> frame
      = m_call_stack.get_current_stack_frame ();

    frame->clear_variables ();
  }

  void tree_evaluator::clear_global_variable (const std::string& name)
  {
    m_call_stack.clear_global_variable (name);
  }

  void
  tree_evaluator::clear_global_variable_pattern (const std::string& pattern)
  {
    m_call_stack.clear_global_variable_pattern (pattern);
  }

  void tree_evaluator::clear_global_variable_regexp(const std::string& pattern)
  {
    m_call_stack.clear_global_variable_regexp (pattern);
  }

  void tree_evaluator::clear_global_variables (void)
  {
    m_call_stack.clear_global_variables ();
  }

  void tree_evaluator::clear_all (bool force)
  {
    // FIXME: should this also clear objects?

    clear_variables ();
    clear_global_variables ();

    symbol_table& symtab = m_interpreter.get_symbol_table ();

    symtab.clear_functions (force);
  }

  void tree_evaluator::clear_symbol (const std::string& name)
  {
    // FIXME: are we supposed to do both here?

    clear_variable (name);

    symbol_table& symtab = m_interpreter.get_symbol_table ();

    symtab.clear_function (name);
  }

  void tree_evaluator::clear_symbol_pattern (const std::string& pattern)
  {
    // FIXME: are we supposed to do both here?

    clear_variable_pattern (pattern);

    symbol_table& symtab = m_interpreter.get_symbol_table ();

    symtab.clear_function_pattern (pattern);
  }

  void tree_evaluator::clear_symbol_regexp (const std::string& pattern)
  {
    // FIXME: are we supposed to do both here?

    clear_variable_regexp (pattern);

    symbol_table& symtab = m_interpreter.get_symbol_table ();

    symtab.clear_function_regexp (pattern);
  }

  std::list<std::string> tree_evaluator::global_variable_names (void) const
  {
    return m_call_stack.global_variable_names ();
  }

  std::list<std::string> tree_evaluator::top_level_variable_names (void) const
  {
    return m_call_stack.top_level_variable_names ();
  }

  std::list<std::string> tree_evaluator::variable_names (void) const
  {
    return m_call_stack.variable_names ();
  }

  // Return a pointer to the user-defined function FNAME.  If FNAME is empty,
  // search backward for the first user-defined function in the
  // current call stack.

  octave_user_code *
  tree_evaluator::get_user_code (const std::string& fname,
                                 const std::string& class_name)
  {
    octave_user_code *user_code = nullptr;

    if (fname.empty ())
      user_code = m_call_stack.debug_user_code ();
    else
      {
        std::string name = fname;

        if (sys::file_ops::dir_sep_char () != '/' && name[0] == '@')
          {
            auto beg = name.begin () + 2;  // never have @/method
            auto end = name.end () - 1;    // never have trailing '/'
            std::replace (beg, end, '/', sys::file_ops::dir_sep_char ());
          }

        std::size_t name_len = name.length ();

        if (name_len > 2 && name.substr (name_len-2) == ".m")
          name = name.substr (0, name_len-2);

        if (name.empty ())
          return nullptr;

        symbol_table& symtab = m_interpreter.get_symbol_table ();

        octave_value fcn;
        std::size_t p2 = std::string::npos;

        if (name[0] == '@')
          {
            std::size_t p1 = name.find (sys::file_ops::dir_sep_char (), 1);

            if (p1 == std::string::npos)
              return nullptr;

            std::string dispatch_type = name.substr (1, p1-1);

            p2 = name.find ('>', p1);

            std::string method = name.substr (p1+1, p2-1);

            fcn = symtab.find_method (method, dispatch_type);
          }
        else if (! class_name.empty ())
          {
            cdef_manager& cdm = m_interpreter.get_cdef_manager ();

            fcn = cdm.find_method (class_name, name);

            // If there is no classdef method, then try legacy classes.
            if (fcn.is_undefined ())
              fcn = symtab.find_method (name, class_name);
          }
        else
          {
            p2 = name.find ('>');

            std::string main_fcn = name.substr (0, p2);

            fcn = symtab.find_function (main_fcn);
          }

        // List of function names sub1>sub2>...
        std::string subfuns;

        if (p2 != std::string::npos)
          subfuns = name.substr (p2+1);

        if (fcn.is_defined () && fcn.is_user_code ())
          user_code = fcn.user_code_value ();

        if (! user_code || subfuns.empty ())
          return user_code;

        fcn = user_code->find_subfunction (subfuns);

        if (fcn.is_undefined ())
          return nullptr;

        user_code = fcn.user_code_value ();
      }

    return user_code;
  }

  std::string
  tree_evaluator::current_function_name (bool skip_first) const
  {
    octave_function *curfcn = m_call_stack.current_function (skip_first);

    if (curfcn)
      return curfcn->name ();

    return "";
  }

  bool
  tree_evaluator::in_user_code (void) const
  {
    return m_call_stack.current_user_code () != nullptr;
  }

  void
  tree_evaluator::visit_decl_command (tree_decl_command& cmd)
  {
    if (m_echo_state)
      {
        int line = cmd.line ();
        if (line < 0)
          line = 1;
        echo_code (line);
        m_echo_file_pos = line + 1;
      }

    if (m_debug_mode)
      do_breakpoint (cmd.is_active_breakpoint (*this));

    // FIXME: tree_decl_init_list is not derived from tree, so should it
    // really have an accept method?

    tree_decl_init_list *init_list = cmd.initializer_list ();

    if (init_list)
      init_list->accept (*this);
  }

  void
  tree_evaluator::visit_decl_elt (tree_decl_elt& elt)
  {
    tree_identifier *id = elt.ident ();

    if (id)
      {
        if (elt.is_global ())
          m_call_stack.make_global (id->symbol ());
        else if (elt.is_persistent ())
          m_call_stack.make_persistent (id->symbol ());
        else
          error ("declaration list element not global or persistent");

        octave_lvalue ult = id->lvalue (*this);

        if (ult.is_undefined ())
          {
            tree_expression *expr = elt.expression ();

            octave_value init_val;

            if (expr)
              init_val = expr->evaluate (*this);
            else
              init_val = Matrix ();

            ult.assign (octave_value::op_asn_eq, init_val);
          }
      }
  }

  template <typename T>
  void
  tree_evaluator::execute_range_loop (const range<T>& rng, int line,
                                      octave_lvalue& ult,
                                      tree_statement_list *loop_body)
  {
    octave_idx_type steps = rng.numel ();

    if (math::isinf (rng.limit ()))
      warning_with_id ("Octave:infinite-loop",
                       "FOR loop limit is infinite, will stop after %"
                       OCTAVE_IDX_TYPE_FORMAT " steps", steps);

    for (octave_idx_type i = 0; i < steps; i++)
      {
        if (m_echo_state)
          m_echo_file_pos = line;

        octave_value val (rng.elem (i));

        ult.assign (octave_value::op_asn_eq, val);

        if (loop_body)
          loop_body->accept (*this);

        if (quit_loop_now ())
          break;
      }
  }

  void
  tree_evaluator::visit_simple_for_command (tree_simple_for_command& cmd)
  {
    int line = cmd.line ();
    if (line < 0)
      line = 1;

    if (m_echo_state)
      {
        echo_code (line);
        line++;
      }

    if (m_debug_mode)
      do_breakpoint (cmd.is_active_breakpoint (*this));

    // FIXME: need to handle PARFOR loops here using cmd.in_parallel ()
    // and cmd.maxproc_expr ();

    unwind_protect_var<bool> upv (m_in_loop_command, true);

    tree_expression *expr = cmd.control_expr ();

    octave_value rhs = expr->evaluate (*this);

    if (rhs.is_undefined ())
      return;

    tree_expression *lhs = cmd.left_hand_side ();

    octave_lvalue ult = lhs->lvalue (*this);

    tree_statement_list *loop_body = cmd.body ();

    if (rhs.is_range ())
      {
        // FIXME: is there a better way to dispatch here?

        if (rhs.is_double_type ())
          {
            execute_range_loop (rhs.range_value (), line, ult, loop_body);
            return;
          }

        // For now, disable all but range<double>.

#if 0
        if (rhs.is_int64_type ())
          {
            execute_range_loop (rhs.int64_range_value (), line, ult, loop_body);
            return;
          }

        if (rhs.is_uint64_type ())
          {
            execute_range_loop (rhs.uint64_range_value (), line, ult, loop_body);
            return;
          }

        if (rhs.is_int32_type ())
          {
            execute_range_loop (rhs.int32_range_value (), line, ult, loop_body);
            return;
          }

        if (rhs.is_uint32_type ())
          {
            execute_range_loop (rhs.uint32_range_value (), line, ult, loop_body);
            return;
          }

        if (rhs.is_int16_type ())
          {
            execute_range_loop (rhs.int16_range_value (), line, ult, loop_body);
            return;
          }

        if (rhs.is_uint16_type ())
          {
            execute_range_loop (rhs.uint16_range_value (), line, ult, loop_body);
            return;
          }

        if (rhs.is_int8_type ())
          {
            execute_range_loop (rhs.int8_range_value (), line, ult, loop_body);
            return;
          }

        if (rhs.is_uint8_type ())
          {
            execute_range_loop (rhs.uint8_range_value (), line, ult, loop_body);
            return;
          }

        if (rhs.is_single_type ())
          {
            execute_range_loop (rhs.float_range_value (), line, ult, loop_body);
            return;
          }
#endif
      }

    if (rhs.is_scalar_type ())
      {
        if (m_echo_state)
          m_echo_file_pos = line;

        ult.assign (octave_value::op_asn_eq, rhs);

        if (loop_body)
          loop_body->accept (*this);

        // Maybe decrement break and continue states.
        quit_loop_now ();

        return;
      }

    // Also handle any range types not explicitly handled above, though
    // not as efficiently as the specialized code above.

    if (rhs.is_range () || rhs.is_matrix_type () || rhs.iscell ()
        || rhs.is_string () || rhs.isstruct ())
      {
        // A matrix or cell is reshaped to 2 dimensions and iterated by
        // columns.

        dim_vector dv = rhs.dims ().redim (2);

        octave_idx_type nrows = dv(0);
        octave_idx_type steps = dv(1);

        octave_value arg = rhs;
        if (rhs.ndims () > 2)
          arg = arg.reshape (dv);

        if (nrows > 0 && steps > 0)
          {
            octave_value_list idx;
            octave_idx_type iidx;

            // for row vectors, use single index to speed things up.
            if (nrows == 1)
              {
                idx.resize (1);
                iidx = 0;
              }
            else
              {
                idx.resize (2);
                idx(0) = octave_value::magic_colon_t;
                iidx = 1;
              }

            for (octave_idx_type i = 1; i <= steps; i++)
              {
                if (m_echo_state)
                  m_echo_file_pos = line;

                // index_op expects one-based indices.
                idx(iidx) = i;
                octave_value val = arg.index_op (idx);

                ult.assign (octave_value::op_asn_eq, val);

                if (loop_body)
                  loop_body->accept (*this);

                if (quit_loop_now ())
                  break;
              }
          }
        else
          {
            // Handle empty cases, while still assigning to loop var.
            ult.assign (octave_value::op_asn_eq, arg);
          }

        return;
      }

    error ("invalid type in for loop expression near line %d, column %d",
           cmd.line (), cmd.column ());
  }

  void
  tree_evaluator::visit_complex_for_command (tree_complex_for_command& cmd)
  {
    int line = cmd.line ();
    if (line < 0)
      line = 1;

    if (m_echo_state)
      {
        echo_code (line);
        line++;
      }

    if (m_debug_mode)
      do_breakpoint (cmd.is_active_breakpoint (*this));

    unwind_protect_var<bool> upv (m_in_loop_command, true);

    tree_expression *expr = cmd.control_expr ();

    octave_value rhs = expr->evaluate (*this);

    if (rhs.is_undefined ())
      return;

    if (! rhs.isstruct ())
      error ("in statement 'for [X, Y] = VAL', VAL must be a structure");

    // Cycle through structure elements.  First element of id_list
    // is set to value and the second is set to the name of the
    // structure element.

    tree_argument_list *lhs = cmd.left_hand_side ();

    auto p = lhs->begin ();

    tree_expression *elt = *p++;

    octave_lvalue val_ref = elt->lvalue (*this);

    elt = *p;

    octave_lvalue key_ref = elt->lvalue (*this);

    const octave_map tmp_val = rhs.map_value ();

    tree_statement_list *loop_body = cmd.body ();

    string_vector keys = tmp_val.keys ();

    octave_idx_type nel = keys.numel ();

    for (octave_idx_type i = 0; i < nel; i++)
      {
        if (m_echo_state)
          m_echo_file_pos = line;

        std::string key = keys[i];

        const Cell val_lst = tmp_val.contents (key);

        octave_idx_type n = val_lst.numel ();

        octave_value val = (n == 1) ? val_lst(0) : octave_value (val_lst);

        val_ref.assign (octave_value::op_asn_eq, val);
        key_ref.assign (octave_value::op_asn_eq, key);

        if (loop_body)
          loop_body->accept (*this);

        if (quit_loop_now ())
          break;
      }
  }

  void tree_evaluator::visit_spmd_command (tree_spmd_command& cmd)
  {
    // For now, we just execute the commands serially.

    tree_statement_list *body = cmd.body ();

    if (body)
      body->accept (*this);
  }

  octave_value
  tree_evaluator::evaluate_anon_fcn_handle (tree_anon_fcn_handle& afh)
  {
    // FIXME: should CMD_LIST be limited to a single expression?
    // I think that is what Matlab does.

    symbol_scope new_scope;
    symbol_scope scope = afh.scope ();
    if (scope)
      new_scope = scope.dup ();

    tree_parameter_list *param_list = afh.parameter_list ();
    tree_parameter_list *param_list_dup
      = param_list ? param_list->dup (new_scope) : nullptr;

    tree_parameter_list *ret_list = nullptr;

    tree_statement_list *stmt_list = nullptr;

    symbol_scope parent_scope = get_current_scope ();

    new_scope.set_parent (parent_scope);
    new_scope.set_primary_parent (parent_scope);

    tree_expression *expr = afh.expression ();
    if (expr)
      {
        tree_expression *expr_dup = expr->dup (new_scope);
        tree_statement *stmt = new tree_statement (expr_dup, nullptr);
        stmt_list = new tree_statement_list (stmt);
      }

    tree_anon_scopes anon_fcn_ctx (afh);

    std::set<std::string> free_vars = anon_fcn_ctx.free_variables ();

    stack_frame::local_vars_map local_vars;

    std::shared_ptr<stack_frame> frame
      = m_call_stack.get_current_stack_frame ();

    for (auto& name : free_vars)
      {
        octave_value val = frame->varval (name);

        if (val.is_defined ())
          local_vars[name] = val;
      }

    octave_user_function *af
      = new octave_user_function (new_scope, param_list_dup, ret_list,
                                  stmt_list);

    octave_function *curr_fcn = m_call_stack.current_function ();

    bool is_nested = false;

    if (curr_fcn)
      {
        // FIXME: maybe it would be better to just stash curr_fcn
        // instead of individual bits of info about it?

        // An anonymous function defined inside another nested function
        // or parent of a nested function also behaves like a nested
        // function.

        if (curr_fcn->is_parent_function () || curr_fcn->is_nested_function ())
          {
            is_nested = true;
            af->mark_as_nested_function ();
            new_scope.set_nesting_depth (parent_scope.nesting_depth () + 1);
          }

        af->stash_dir_name (curr_fcn->dir_name ());

        new_scope.cache_fcn_file_name (curr_fcn->fcn_file_name ());
        new_scope.cache_dir_name (curr_fcn->dir_name ());

        // The following is needed so that class method dispatch works
        // properly for anonymous functions that wrap class methods.

        if (curr_fcn->is_class_method () || curr_fcn->is_class_constructor ())
          af->stash_dispatch_class (curr_fcn->dispatch_class ());

        af->stash_fcn_file_name (curr_fcn->fcn_file_name ());
      }

    af->mark_as_anonymous_function ();

    octave_value ov_fcn (af);

    return (is_nested
            ? octave_value (new octave_fcn_handle (ov_fcn, local_vars, frame))
            : octave_value (new octave_fcn_handle (ov_fcn, local_vars)));
  }

  octave_value_list
  tree_evaluator::execute_builtin_function (octave_builtin& builtin_function,
                                            int nargout,
                                            const octave_value_list& args)
  {
    octave_value_list retval;

    if (args.has_magic_colon ())
      error ("invalid use of colon in function argument list");

    profiler::enter<octave_builtin> block (m_profiler, builtin_function);

    octave_builtin::fcn fcn = builtin_function.function ();

    if (fcn)
      retval = (*fcn) (args, nargout);
    else
      {
        octave_builtin::meth meth = builtin_function.method ();

        retval = (*meth) (m_interpreter, args, nargout);
      }

    // Do not allow null values to be returned from functions.
    // FIXME: perhaps true builtins should be allowed?

    retval.make_storable_values ();

    // Fix the case of a single undefined value.
    // This happens when a compiled function uses
    //
    //   octave_value retval;
    //
    // instead of
    //
    //   octave_value_list retval;
    //
    // the idiom is very common, so we solve that here.

    if (retval.length () == 1 && retval.xelem (0).is_undefined ())
      retval.clear ();

    return retval;
  }

  octave_value_list
  tree_evaluator::execute_mex_function (octave_mex_function& mex_function,
                                        int nargout,
                                        const octave_value_list& args)
  {
    octave_value_list retval;

    if (args.has_magic_colon ())
      error ("invalid use of colon in function argument list");

    profiler::enter<octave_mex_function> block (m_profiler, mex_function);

    retval = call_mex (mex_function, args, nargout);

    return retval;
  }

  octave_value_list
  tree_evaluator::execute_user_script (octave_user_script& user_script,
                                       int nargout,
                                       const octave_value_list& args)
  {
    octave_value_list retval;

    std::string file_name = user_script.fcn_file_name ();

    if (args.length () != 0 || nargout != 0)
      error ("invalid call to script %s", file_name.c_str ());

    tree_statement_list *cmd_list = user_script.body ();

    if (! cmd_list)
      return retval;

    // FIXME: Maybe this check belongs in the places where we push a new
    // stack frame?  Or in the call_stack push method itself?

    if (m_call_stack.size () >= static_cast<std::size_t> (m_max_recursion_depth))
      error ("max_recursion_depth exceeded");

    unwind_protect_var<stmt_list_type> upv (m_statement_context, SC_SCRIPT);

    profiler::enter<octave_user_script> block (m_profiler, user_script);

    if (echo ())
      push_echo_state (tree_evaluator::ECHO_SCRIPTS, file_name);

    // FIXME: Should we be using tree_evaluator::eval here?

    cmd_list->accept (*this);

    if (m_returning)
      m_returning = 0;

    if (m_breaking)
      m_breaking--;

    return retval;
  }

  void
  tree_evaluator::visit_octave_user_script (octave_user_script&)
  {
    // ??
    panic_impossible ();
  }

  octave_value_list
  tree_evaluator::execute_user_function (octave_user_function& user_function,
                                         int nargout,
                                         const octave_value_list& xargs)
  {
    octave_value_list retval;

    // If this function is a classdef constructor, extract the first input
    // argument, which must be the partially constructed object instance.

    octave_value_list args (xargs);
    octave_value_list ret_args;

    int nargin = args.length ();

    if (user_function.is_classdef_constructor ())
      {
        if (nargin > 0)
          {
            ret_args = args.slice (0, 1, true);
            --nargin;
            args = args.slice (1, nargin, true);
          }
        else
          panic_impossible ();
      }

    // FIXME: this probably shouldn't be a double-precision matrix.
    Matrix ignored_outputs = ignored_fcn_outputs ();

    tree_parameter_list *param_list = user_function.parameter_list ();

    bool takes_varargs = false;
    int max_inputs = 0;

    if (param_list)
      {
        takes_varargs = param_list->takes_varargs ();
        max_inputs = param_list->length ();
      }

    if (! takes_varargs && nargin > max_inputs)
      {
        std::string name = user_function.name ();

        if (name.empty ())
          name = "@<anonymous>";

        error_with_id ("Octave:invalid-fun-call",
                       "%s: function called with too many inputs",
                       name.c_str ());
      }

    define_parameter_list_from_arg_vector (param_list, args);

    tree_parameter_list *ret_list = user_function.return_list ();

    if (ret_list && ! ret_list->takes_varargs ())
      {
        int max_outputs = ret_list->length ();

        if (nargout > max_outputs)
          {
            std::string name = user_function.name ();

            error_with_id ("Octave:invalid-fun-call",
                           "%s: function called with too many outputs",
                           name.c_str ());
          }
      }

    bind_auto_fcn_vars (xargs.name_tags (), ignored_outputs, nargin,
                        nargout, user_function.takes_varargs (),
                        user_function.all_va_args (args));

    // For classdef constructor, pre-populate the output arguments
    // with the pre-initialized object instance, extracted above.

    if (user_function.is_classdef_constructor ())
      {
        if (! ret_list)
          error ("%s: invalid classdef constructor, no output argument defined",
                 user_function.dispatch_class ().c_str ());

        define_parameter_list_from_arg_vector (ret_list, ret_args);
      }

    // FIXME: Maybe this check belongs in the places where we push a
    // new stack frame?  Or in the call_stack push method itself?

    if (m_call_stack.size () >= static_cast<std::size_t> (m_max_recursion_depth))
      error ("max_recursion_depth exceeded");

    unwind_action act2 ([&user_function] () {
                          user_function.restore_warning_states ();
                        });

    // Evaluate the commands that make up the function.

    unwind_protect_var<stmt_list_type> upv (m_statement_context, SC_FUNCTION);

    tree_statement_list *cmd_list = user_function.body ();

    if (cmd_list)
      {
        profiler::enter<octave_user_function>
          block (m_profiler, user_function);

        if (echo ())
          push_echo_state (tree_evaluator::ECHO_FUNCTIONS,
                           user_function.fcn_file_name ());

        if (user_function.is_special_expr ())
          {
            panic_if (cmd_list->length () != 1);

            tree_statement *stmt = cmd_list->front ();

            tree_expression *expr = stmt->expression ();

            if (expr)
              {
                m_call_stack.set_location (stmt->line (), stmt->column ());

                retval = expr->evaluate_n (*this, nargout);
              }
          }
        else
          cmd_list->accept (*this);

        if (m_returning)
          m_returning = 0;

        if (m_breaking)
          m_breaking--;
      }

    // Copy return values out.

    if (ret_list && ! user_function.is_special_expr ())
      {
        Cell varargout;

        if (ret_list->takes_varargs ())
          {
            octave_value varargout_varval = varval ("varargout");

            if (varargout_varval.is_defined ())
              varargout = varargout_varval.xcell_value ("varargout must be a cell array object");
          }

        retval = convert_return_list_to_const_vector (ret_list, nargout,
                                                      ignored_outputs,
                                                      varargout);
      }

    return retval;
  }

  void
  tree_evaluator::visit_octave_user_function (octave_user_function&)
  {
    // ??
    panic_impossible ();
  }

  void
  tree_evaluator::visit_octave_user_function_header (octave_user_function&)
  {
    panic_impossible ();
  }

  void
  tree_evaluator::visit_octave_user_function_trailer (octave_user_function&)
  {
    panic_impossible ();
  }

  void
  tree_evaluator::visit_function_def (tree_function_def& cmd)
  {
    octave_value fcn = cmd.function ();

    octave_function *f = fcn.function_value ();

    if (f)
      {
        std::string nm = f->name ();

        symbol_table& symtab = m_interpreter.get_symbol_table ();

        symtab.install_cmdline_function (nm, fcn);

        // Make sure that any variable with the same name as the new
        // function is cleared.

        assign (nm);
      }
  }

  void
  tree_evaluator::visit_identifier (tree_identifier&)
  {
    panic_impossible ();
  }

  void
  tree_evaluator::visit_if_clause (tree_if_clause&)
  {
    panic_impossible ();
  }

  void
  tree_evaluator::visit_if_command (tree_if_command& cmd)
  {
    if (m_echo_state)
      {
        int line = cmd.line ();
        if (line < 0)
          line = 1;
        echo_code (line);
        m_echo_file_pos = line + 1;
      }

    // FIXME: tree_if_command_list is not derived from tree, so should it
    // really have an accept method?

    tree_if_command_list *lst = cmd.cmd_list ();

    if (lst)
      lst->accept (*this);
  }

  void
  tree_evaluator::visit_if_command_list (tree_if_command_list& lst)
  {
    for (tree_if_clause *tic : lst)
      {
        tree_expression *expr = tic->condition ();

        if (! (in_debug_repl ()
               && m_call_stack.current_frame () == m_debug_frame))
          m_call_stack.set_location (tic->line (), tic->column ());

        if (m_debug_mode && ! tic->is_else_clause ())
          do_breakpoint (tic->is_active_breakpoint (*this));

        if (tic->is_else_clause () || is_logically_true (expr, "if"))
          {
            tree_statement_list *stmt_lst = tic->commands ();

            if (stmt_lst)
              stmt_lst->accept (*this);

            break;
          }
      }
  }

  void
  tree_evaluator::visit_index_expression (tree_index_expression&)
  {
    panic_impossible ();
  }

  void
  tree_evaluator::visit_matrix (tree_matrix&)
  {
    panic_impossible ();
  }

  void
  tree_evaluator::visit_cell (tree_cell&)
  {
    panic_impossible ();
  }

  void
  tree_evaluator::visit_multi_assignment (tree_multi_assignment&)
  {
    panic_impossible ();
  }

  void
  tree_evaluator::visit_no_op_command (tree_no_op_command& cmd)
  {
    if (m_echo_state)
      {
        int line = cmd.line ();
        if (line < 0)
          line = 1;
        echo_code (line);
        m_echo_file_pos = line + 1;
      }

    if (m_debug_mode && cmd.is_end_of_fcn_or_script ())
      do_breakpoint (cmd.is_active_breakpoint (*this), true);
  }

  void
  tree_evaluator::visit_constant (tree_constant&)
  {
    panic_impossible ();
  }

  void
  tree_evaluator::visit_fcn_handle (tree_fcn_handle&)
  {
    panic_impossible ();
  }

  void
  tree_evaluator::visit_parameter_list (tree_parameter_list&)
  {
    panic_impossible ();
  }

  void
  tree_evaluator::visit_postfix_expression (tree_postfix_expression&)
  {
    panic_impossible ();
  }

  void
  tree_evaluator::visit_prefix_expression (tree_prefix_expression&)
  {
    panic_impossible ();
  }

  void
  tree_evaluator::visit_return_command (tree_return_command& cmd)
  {
    if (m_echo_state)
      {
        int line = cmd.line ();
        if (line < 0)
          line = 1;
        echo_code (line);
        m_echo_file_pos = line + 1;
      }

    if (m_debug_mode)
      do_breakpoint (cmd.is_active_breakpoint (*this));

    // Act like dbcont.

    if (in_debug_repl () && m_call_stack.current_frame () == m_debug_frame)
      dbcont ();
    else if (m_statement_context == SC_FUNCTION
             || m_statement_context == SC_SCRIPT
             || m_in_loop_command)
      m_returning = 1;
  }

  void
  tree_evaluator::visit_simple_assignment (tree_simple_assignment&)
  {
    panic_impossible ();
  }

  void
  tree_evaluator::visit_statement (tree_statement& stmt)
  {
    tree_command *cmd = stmt.command ();
    tree_expression *expr = stmt.expression ();

    if (cmd || expr)
      {
        if (! (in_debug_repl ()
               && m_call_stack.current_frame () == m_debug_frame))
          m_call_stack.set_location (stmt.line (), stmt.column ());

        try
          {
            if (cmd)
              {
                unwind_protect_var<const std::list<octave_lvalue> *>
                  upv (m_lvalue_list, nullptr);

                cmd->accept (*this);
              }
            else
              {
                if (m_echo_state)
                  {
                    int line = stmt.line ();
                    if (line < 0)
                      line = 1;
                    echo_code (line);
                    m_echo_file_pos = line + 1;
                  }

                if (m_debug_mode)
                  do_breakpoint (expr->is_active_breakpoint (*this));

                // FIXME: maybe all of this should be packaged in
                // one virtual function that returns a flag saying whether
                // or not the expression will take care of binding ans and
                // printing the result.

                // FIXME: it seems that we should just have to
                // evaluate the expression and that should take care of
                // everything, binding ans as necessary?

                octave_value tmp_result = expr->evaluate (*this, 0);

                if (tmp_result.is_defined ())
                  {
                    bool do_bind_ans = false;

                    if (expr->is_identifier ())
                      do_bind_ans = ! is_variable (expr);
                    else
                      do_bind_ans = ! expr->is_assignment_expression ();

                    if (do_bind_ans)
                      bind_ans (tmp_result, expr->print_result ()
                                && statement_printing_enabled ());
                  }
              }
          }
        catch (const std::bad_alloc&)
          {
            // FIXME: We want to use error_with_id here so that give users
            // control over this error message but error_with_id will
            // require some memory allocations.  Is there anything we can
            // do to make those more likely to succeed?

            error_with_id ("Octave:bad-alloc",
                           "out of memory or dimension too large for Octave's index type");
          }
        catch (const interrupt_exception&)
          {
            // If we are debugging, then continue with next statement.
            // Otherwise, jump out of here.

            if (m_debug_mode)
              m_interpreter.recover_from_exception ();
            else
              throw;
          }
        catch (const execution_exception& ee)
          {
            error_system& es = m_interpreter.get_error_system ();

            if ((m_interpreter.interactive ()
                 || application::forced_interactive ())
                && ((es.debug_on_error ()
                     && m_bp_table.debug_on_err (es.last_error_id ()))
                    || (es.debug_on_caught ()
                        && m_bp_table.debug_on_caught (es.last_error_id ())))
                && in_user_code ())
              {
                es.save_exception (ee);
                es.display_exception (ee);

                enter_debugger ();

                // It doesn't make sense to continue execution after an
                // error occurs so force the debugger to quit all debug
                // levels and return the the top prompt.

                throw quit_debug_exception (true);
              }
            else
              throw;
          }
      }
  }

  void
  tree_evaluator::visit_statement_list (tree_statement_list& lst)
  {
    // FIXME: commented out along with else clause below.
    // static octave_value_list empty_list;

    auto p = lst.begin ();

    if (p != lst.end ())
      {
        while (true)
          {
            tree_statement *elt = *p++;

            if (! elt)
              error ("invalid statement found in statement list!");

            octave_quit ();

            elt->accept (*this);

            if (m_breaking || m_continuing)
              break;

            if (m_returning)
              break;

            if (p == lst.end ())
              break;
            else
              {
                // Clear previous values before next statement is
                // evaluated so that we aren't holding an extra
                // reference to a value that may be used next.  For
                // example, in code like this:
                //
                //   X = rand (N);  # refcount for X should be 1
                //                  # after this statement
                //
                //   X(idx) = val;  # no extra copy of X should be
                //                  # needed, but we will be faked
                //                  # out if retval is not cleared
                //                  # between statements here

                //              result_values = empty_list;
              }
          }
      }
  }

  void
  tree_evaluator::visit_switch_case (tree_switch_case&)
  {
    panic_impossible ();
  }

  void
  tree_evaluator::visit_switch_case_list (tree_switch_case_list&)
  {
    panic_impossible ();
  }

  void
  tree_evaluator::visit_switch_command (tree_switch_command& cmd)
  {
    if (m_echo_state)
      {
        int line = cmd.line ();
        if (line < 0)
          line = 1;
        echo_code (line);
        m_echo_file_pos = line + 1;
      }

    if (m_debug_mode)
      do_breakpoint (cmd.is_active_breakpoint (*this));

    tree_expression *expr = cmd.switch_value ();

    if (! expr)
      error ("missing value in switch command near line %d, column %d",
             cmd.line (), cmd.column ());

    octave_value val = expr->evaluate (*this);

    tree_switch_case_list *lst = cmd.case_list ();

    if (lst)
      {
        for (tree_switch_case *t : *lst)
          {
            if (t->is_default_case () || switch_case_label_matches (t, val))
              {
                tree_statement_list *stmt_lst = t->commands ();

                if (stmt_lst)
                  stmt_lst->accept (*this);

                break;
              }
          }
      }
  }

  void
  tree_evaluator::visit_try_catch_command (tree_try_catch_command& cmd)
  {
    if (m_echo_state)
      {
        int line = cmd.line ();
        if (line < 0)
          line = 1;
        echo_code (line);
        m_echo_file_pos = line + 1;
      }

    bool execution_error = false;
    octave_scalar_map err_map;

    tree_statement_list *try_code = cmd.body ();

    if (try_code)
      {
        // unwind frame before catch block

        unwind_protect frame;

        interpreter_try (frame);

        // The catch code is *not* added to unwind_protect stack; it
        // doesn't need to be run on interrupts.

        try
          {
            try_code->accept (*this);
          }
        catch (const execution_exception& ee)
          {
            execution_error = true;

            error_system& es = m_interpreter.get_error_system ();

            es.save_exception (ee);

            err_map.assign ("message", es.last_error_message ());
            err_map.assign ("identifier", es.last_error_id ());
            err_map.assign ("stack", es.last_error_stack ());

            m_interpreter.recover_from_exception ();
          }

        // Actions attached to unwind_protect frame will run here, prior
        // to executing the catch block.
      }

    if (execution_error)
      {
        tree_statement_list *catch_code = cmd.cleanup ();

        if (catch_code)
          {
            tree_identifier *expr_id = cmd.identifier ();

            if (expr_id)
              {
                octave_lvalue ult = expr_id->lvalue (*this);

                ult.assign (octave_value::op_asn_eq, err_map);
              }

            // perform actual "catch" block
            catch_code->accept (*this);
          }
      }
  }

  void
  tree_evaluator::do_unwind_protect_cleanup_code (tree_statement_list *list)
  {
    unwind_protect frame;

    frame.protect_var (octave_interrupt_state);
    octave_interrupt_state = 0;

    // We want to preserve the last location info for possible
    // backtracking.

    frame.add (&call_stack::set_line, &m_call_stack,
               m_call_stack.current_line ());

    frame.add (&call_stack::set_column, &m_call_stack,
               m_call_stack.current_column ());

    // Similarly, if we have seen a return or break statement, allow all
    // the cleanup code to run before returning or handling the break.
    // We don't have to worry about continue statements because they can
    // only occur in loops.

    frame.protect_var (m_returning);
    m_returning = 0;

    frame.protect_var (m_breaking);
    m_breaking = 0;

    try
      {
        if (list)
          list->accept (*this);
      }
    catch (const execution_exception& ee)
      {
        error_system& es = m_interpreter.get_error_system ();

        es.save_exception (ee);
        m_interpreter.recover_from_exception ();

        if (m_breaking || m_returning)
          frame.discard (2);
        else
          frame.run (2);

        frame.discard (2);

        throw;
      }

    // The unwind_protects are popped off the stack in the reverse of
    // the order they are pushed on.

    // FIXME: these statements say that if we see a break or
    // return statement in the cleanup block, that we want to use the
    // new value of the breaking or returning flag instead of restoring
    // the previous value.  Is that the right thing to do?  I think so.
    // Consider the case of
    //
    //   function foo ()
    //     unwind_protect
    //       fprintf (stderr, "1: this should always be executed\n");
    //       break;
    //       fprintf (stderr, "1: this should never be executed\n");
    //     unwind_protect_cleanup
    //       fprintf (stderr, "2: this should always be executed\n");
    //       return;
    //       fprintf (stderr, "2: this should never be executed\n");
    //     end_unwind_protect
    //   endfunction
    //
    // If we reset the value of the breaking flag, both the returning
    // flag and the breaking flag will be set, and we shouldn't have
    // both.  So, use the most recent one.  If there is no return or
    // break in the cleanup block, the values should be reset to
    // whatever they were when the cleanup block was entered.

    if (m_breaking || m_returning)
      frame.discard (2);
    else
      frame.run (2);
  }

  void
  tree_evaluator::visit_unwind_protect_command (tree_unwind_protect_command& cmd)
  {
    if (m_echo_state)
      {
        int line = cmd.line ();
        if (line < 0)
          line = 1;
        echo_code (line);
        m_echo_file_pos = line + 1;
      }

    tree_statement_list *cleanup_code = cmd.cleanup ();

    tree_statement_list *unwind_protect_code = cmd.body ();

    if (unwind_protect_code)
      {
        try
          {
            unwind_protect_code->accept (*this);
          }
        catch (const execution_exception& ee)
          {
            error_system& es = m_interpreter.get_error_system ();

            // FIXME: Maybe we should be able to temporarily set the
            // interpreter's exception handling state to something "safe"
            // while the cleanup block runs instead of just resetting it
            // here?
            es.save_exception (ee);
            m_interpreter.recover_from_exception ();

            // Run the cleanup code on exceptions, so that it is run even
            // in case of interrupt or out-of-memory.
            do_unwind_protect_cleanup_code (cleanup_code);

            // If an error occurs inside the cleanup code, a new
            // exception will be thrown instead of the original.
            throw;
          }
        catch (const interrupt_exception&)
          {
            // The comments above apply here as well.
            m_interpreter.recover_from_exception ();
            do_unwind_protect_cleanup_code (cleanup_code);
            throw;
          }

        // Also execute the unwind_protect_cleanump code if the
        // unwind_protect block runs without error.
        do_unwind_protect_cleanup_code (cleanup_code);
      }
  }

  void
  tree_evaluator::visit_while_command (tree_while_command& cmd)
  {
    int line = cmd.line ();
    if (line < 0)
      line = 1;

    if (m_echo_state)
      {
        echo_code (line);
        line++;
      }

    unwind_protect_var<bool> upv (m_in_loop_command, true);

    tree_expression *expr = cmd.condition ();

    if (! expr)
      panic_impossible ();

    for (;;)
      {
        if (m_echo_state)
          m_echo_file_pos = line;

        if (m_debug_mode)
          do_breakpoint (cmd.is_active_breakpoint (*this));

        if (is_logically_true (expr, "while"))
          {
            tree_statement_list *loop_body = cmd.body ();

            if (loop_body)
              loop_body->accept (*this);

            if (quit_loop_now ())
              break;
          }
        else
          break;
      }
  }

  void
  tree_evaluator::visit_do_until_command (tree_do_until_command& cmd)
  {
    int line = cmd.line ();
    if (line < 0)
      line = 1;

    if (m_echo_state)
      {
        echo_code (line);
        line++;
      }

    unwind_protect_var<bool> upv (m_in_loop_command, true);

    tree_expression *expr = cmd.condition ();

    if (! expr)
      panic_impossible ();

    for (;;)
      {
        if (m_echo_state)
          m_echo_file_pos = line;

        tree_statement_list *loop_body = cmd.body ();

        if (loop_body)
          loop_body->accept (*this);

        if (quit_loop_now ())
          break;

        if (m_debug_mode)
          do_breakpoint (cmd.is_active_breakpoint (*this));

        if (is_logically_true (expr, "do-until"))
          break;
      }
  }

  void
  tree_evaluator::visit_superclass_ref (tree_superclass_ref&)
  {
    panic_impossible ();
  }

  void
  tree_evaluator::visit_metaclass_query (tree_metaclass_query&)
  {
    panic_impossible ();
  }

  void tree_evaluator::bind_ans (const octave_value& val, bool print)
  {
    static std::string ans = "ans";

    if (val.is_defined ())
      {
        if (val.is_cs_list ())
          {
            octave_value_list lst = val.list_value ();

            for (octave_idx_type i = 0; i < lst.length (); i++)
              bind_ans (lst(i), print);
          }
        else
          {
            // FIXME: Maybe assign could also return the assigned value,
            // just for convenience?

            assign (ans, val);

            if (print)
              {
                // Use varval instead of displaying VAL directly so that
                // we get the right type and value for things like
                // magic_int values that may mutate when stored.

                octave_value_list args = ovl (varval (ans));
                args.stash_name_tags (string_vector (ans));
                feval ("display", args);
              }
          }
      }
  }

  void
  tree_evaluator::do_breakpoint (tree_statement& stmt)
  {
    do_breakpoint (stmt.is_active_breakpoint (*this),
                   stmt.is_end_of_fcn_or_script ());
  }

  void
  tree_evaluator::do_breakpoint (bool is_breakpoint,
                                 bool is_end_of_fcn_or_script)
  {
    bool break_on_this_statement = false;

    if (is_breakpoint)
      break_on_this_statement = true;
    else if (m_dbstep_flag > 0)
      {
        if (m_call_stack.current_frame () == m_debug_frame)
          {
            if (m_dbstep_flag == 1 || is_end_of_fcn_or_script)
              {
                // We get here if we are doing a "dbstep" or a "dbstep N" and
                // the count has reached 1 so that we must stop and return to
                // debug prompt.  Alternatively, "dbstep N" has been used but
                // the end of the frame has been reached so we stop at the last
                // line and return to prompt.

                break_on_this_statement = true;
              }
            else
              {
                // Executing "dbstep N".  Decrease N by one and continue.

                m_dbstep_flag--;
              }

          }
        else if (m_dbstep_flag == 1
                 && m_call_stack.current_frame () < m_debug_frame)
          {
            // We stepped out from the end of a function.

            m_debug_frame = m_call_stack.current_frame ();

            break_on_this_statement = true;
          }
      }
    else if (m_dbstep_flag == -1)
      {
        // We get here if we are doing a "dbstep in".

        break_on_this_statement = true;

        m_debug_frame = m_call_stack.current_frame ();
      }
    else if (m_dbstep_flag == -2)
      {
        // We get here if we are doing a "dbstep out".  Check for end of
        // function and whether the current frame is the same as the
        // cached value because we want to step out from the frame where
        // "dbstep out" was evaluated, not from any functions called from
        // that frame.

        if (is_end_of_fcn_or_script
            && m_call_stack.current_frame () == m_debug_frame)
          m_dbstep_flag = -1;
      }

    if (! break_on_this_statement)
      break_on_this_statement = m_break_on_next_stmt;

    m_break_on_next_stmt = false;

    if (break_on_this_statement)
      {
        m_dbstep_flag = 0;

        enter_debugger ();
      }
  }

  bool
  tree_evaluator::is_logically_true (tree_expression *expr,
                                     const char *warn_for)
  {
    bool expr_value = false;

    m_call_stack.set_location (expr->line (), expr->column ());

    octave_value t1 = expr->evaluate (*this);

    if (t1.is_defined ())
      return t1.is_true ();
    else
      error ("%s: undefined value used in conditional expression", warn_for);

    return expr_value;
  }

  octave_value
  tree_evaluator::max_recursion_depth (const octave_value_list& args,
                                       int nargout)
  {
    return set_internal_variable (m_max_recursion_depth, args, nargout,
                                  "max_recursion_depth", 0);
  }

  symbol_info_list
  tree_evaluator::glob_symbol_info (const std::string& pattern) const
  {
    return m_call_stack.glob_symbol_info (pattern);
  }

  symbol_info_list
  tree_evaluator::regexp_symbol_info (const std::string& pattern) const
  {
    return m_call_stack.regexp_symbol_info (pattern);
  }

  symbol_info_list
  tree_evaluator::get_symbol_info (void)
  {
    return m_call_stack.get_symbol_info ();
  }

  symbol_info_list
  tree_evaluator::top_scope_symbol_info (void) const
  {
    return m_call_stack.top_scope_symbol_info ();
  }

  octave_map tree_evaluator::get_autoload_map (void) const
  {
    Cell fcn_names (dim_vector (m_autoload_map.size (), 1));
    Cell file_names (dim_vector (m_autoload_map.size (), 1));

    octave_idx_type i = 0;
    for (const auto& fcn_fname : m_autoload_map)
      {
        fcn_names(i) = fcn_fname.first;
        file_names(i) = fcn_fname.second;

        i++;
      }

    octave_map m;

    m.assign ("function", fcn_names);
    m.assign ("file", file_names);

    return m;
  }

  std::string tree_evaluator::lookup_autoload (const std::string& nm) const
  {
    std::string retval;

    auto p = m_autoload_map.find (nm);

    if (p != m_autoload_map.end ())
      {
        load_path& lp = m_interpreter.get_load_path ();

        retval = lp.find_file (p->second);
      }

    return retval;
  }

  std::list<std::string> tree_evaluator::autoloaded_functions (void) const
  {
    std::list<std::string> names;

    for (const auto& fcn_fname : m_autoload_map)
      names.push_back (fcn_fname.first);

    return names;
  }

  std::list<std::string>
  tree_evaluator::reverse_lookup_autoload (const std::string& nm) const
  {
    std::list<std::string> names;

    for (const auto& fcn_fname : m_autoload_map)
      if (nm == fcn_fname.second)
        names.push_back (fcn_fname.first);

    return names;
  }

  void tree_evaluator::add_autoload (const std::string& fcn,
                                     const std::string& nm)
  {
    std::string file_name = check_autoload_file (nm);

    m_autoload_map[fcn] = file_name;
  }

  void tree_evaluator::remove_autoload (const std::string& fcn,
                                        const std::string& nm)
  {
    check_autoload_file (nm);

    // Remove function from symbol table and autoload map.
    symbol_table& symtab = m_interpreter.get_symbol_table ();

    symtab.clear_dld_function (fcn);

    m_autoload_map.erase (fcn);
  }

  octave_value
  tree_evaluator::whos_line_format (const octave_value_list& args, int nargout)
  {
    return set_internal_variable (m_whos_line_format, args, nargout,
                                  "whos_line_format");
  }

  octave_value
  tree_evaluator::silent_functions (const octave_value_list& args, int nargout)
  {
    return set_internal_variable (m_silent_functions, args, nargout,
                                  "silent_functions");
  }

  octave_value
  tree_evaluator::string_fill_char (const octave_value_list& args, int nargout)
  {
    return set_internal_variable (m_string_fill_char, args, nargout,
                                  "string_fill_char");
  }

  // Final step of processing an indexing error.  Add the name of the
  // variable being indexed, if any, then issue an error.  (Will this also
  // be needed by pt-lvalue, which calls subsref?)

  void tree_evaluator::final_index_error (index_exception& ie,
                                          const tree_expression *expr)
  {
    std::string extra_message;

    if (is_variable (expr))
      {
        std::string var = expr->name ();

        ie.set_var (var);

        symbol_table& symtab = m_interpreter.get_symbol_table ();

        octave_value fcn = symtab.find_function (var);

        if (fcn.is_function ())
          {
            octave_function *fp = fcn.function_value ();

            if (fp && fp->name () == var)
              extra_message
                = " (note: variable '" + var + "' shadows function)";
          }
      }

    std::string msg = ie.message () + extra_message;

    error_with_id (ie.err_id (), "%s", msg.c_str ());
  }

  octave_value
  tree_evaluator::do_who (int argc, const string_vector& argv,
                          bool return_list, bool verbose)
  {
    return m_call_stack.do_who (argc, argv, return_list, verbose);
  }

  octave_value_list
  tree_evaluator::make_value_list (tree_argument_list *args,
                                   const string_vector& arg_nm)
  {
    octave_value_list retval;

    if (args)
      {
        unwind_protect_var<const std::list<octave_lvalue> *>
          upv (m_lvalue_list, nullptr);

        int len = args->length ();

        unwind_protect_var<int> upv2 (m_index_position);
        unwind_protect_var<int> upv3 (m_num_indices);

        m_num_indices = len;

        std::list<octave_value> arg_vals;

        int k = 0;

        for (auto elt : *args)
          {
            // FIXME: is it possible for elt to be invalid?

            if (! elt)
              break;

            m_index_position = k++;

            octave_value tmp = elt->evaluate (*this);

            if (tmp.is_cs_list ())
              {
                octave_value_list tmp_ovl = tmp.list_value ();

                for (octave_idx_type i = 0; i < tmp_ovl.length (); i++)
                  arg_vals.push_back (tmp_ovl(i));
              }
            else if (tmp.is_defined ())
              arg_vals.push_back (tmp);
          }

        retval = octave_value_list (arg_vals);
      }

    octave_idx_type n = retval.length ();

    if (n > 0)
      retval.stash_name_tags (arg_nm);

    return retval;
  }

  std::list<octave_lvalue>
  tree_evaluator::make_lvalue_list (tree_argument_list *lhs)
  {
    std::list<octave_lvalue> retval;

    for (tree_expression *elt : *lhs)
      retval.push_back (elt->lvalue (*this));

    return retval;
  }

  void
  tree_evaluator::push_echo_state (int type, const std::string& file_name,
                                   int pos)
  {
    unwind_protect *frame = m_call_stack.curr_fcn_unwind_protect_frame ();

    if (frame)
      {
        push_echo_state_cleanup (*frame);

        set_echo_state (type, file_name, pos);
      }
  }

  void
  tree_evaluator::set_echo_state (int type, const std::string& file_name,
                                  int pos)
  {
    m_echo_state = echo_this_file (file_name, type);
    m_echo_file_name = file_name;
    m_echo_file_pos = pos;
  }

  void
  tree_evaluator::uwp_set_echo_state (bool state, const std::string& file_name,
                                      int pos)
  {
    m_echo_state = state;
    m_echo_file_name = file_name;
    m_echo_file_pos = pos;
  }

  void
  tree_evaluator::maybe_set_echo_state (void)
  {
    octave_function *caller = caller_function ();

    if (caller && caller->is_user_code ())
      {
        octave_user_code *fcn = dynamic_cast<octave_user_code *> (caller);

        int type = fcn->is_user_function () ? ECHO_FUNCTIONS : ECHO_SCRIPTS;

        std::string file_name = fcn->fcn_file_name ();

        // We want the line where "echo" was called, not the line number
        // stored in the stack frame that was created for the echo
        // function (that will always be -1).

        int pos = m_call_stack.current_user_code_line ();

        if (pos < 0)
          pos = 1;

        set_echo_state (type, file_name, pos);
      }
  }

  void
  tree_evaluator::push_echo_state_cleanup (unwind_protect& frame)
  {
    frame.add (&tree_evaluator::uwp_set_echo_state, this,
               m_echo_state, m_echo_file_name, m_echo_file_pos);
  }

  bool tree_evaluator::maybe_push_echo_state_cleanup (void)
  {
    // This function is expected to be called from ECHO, which would be
    // the top of the call stack.  If the caller of ECHO is a
    // user-defined function or script, then set up unwind-protect
    // elements to restore echo state.

    unwind_protect *frame = m_call_stack.curr_fcn_unwind_protect_frame ();

    if (frame)
      {
        push_echo_state_cleanup (*frame);
        return true;
      }

    return false;
  }


  octave_value
  tree_evaluator::echo (const octave_value_list& args, int)
  {
    bool cleanup_pushed = maybe_push_echo_state_cleanup ();

    string_vector argv = args.make_argv ();

    switch (args.length ())
      {
      case 0:
        if ((m_echo & ECHO_SCRIPTS) || (m_echo & ECHO_FUNCTIONS))
          {
            m_echo = ECHO_OFF;
            m_echo_files.clear ();
          }
        else
          m_echo = ECHO_SCRIPTS;
        break;

      case 1:
        {
          std::string arg0 = argv[0];

          if (arg0 == "on")
            m_echo = ECHO_SCRIPTS;
          else if (arg0 == "off")
            m_echo = ECHO_OFF;
          else
            {
              std::string file = fcn_file_in_path (arg0);
              file = sys::env::make_absolute (file);

              if (file.empty ())
                error ("echo: no such file %s", arg0.c_str ());

              if (m_echo & ECHO_ALL)
                {
                  // Echo is enabled for all functions, so turn it off
                  // for this one.

                  m_echo_files[file] = false;
                }
              else
                {
                  // Echo may be enabled for specific functions.

                  auto p = m_echo_files.find (file);

                  if (p == m_echo_files.end ())
                    {
                      // Not this one, so enable it.

                      m_echo |= ECHO_FUNCTIONS;
                      m_echo_files[file] = true;
                    }
                  else
                    {
                      // This one is already in the list.  Flip the
                      // status for it.

                      p->second = ! p->second;
                    }
                }
            }
        }
        break;

      case 2:
        {
          std::string arg0 = argv[0];
          std::string arg1 = argv[1];

          if (arg1 == "on" || arg1 == "off")
            std::swap (arg0, arg1);

          if (arg0 == "on")
            {
              if (arg1 == "all")
                {
                  m_echo = (ECHO_SCRIPTS | ECHO_FUNCTIONS | ECHO_ALL);
                  m_echo_files.clear ();
                }
              else
                {
                  std::string file = fcn_file_in_path (arg1);
                  file = sys::env::make_absolute (file);

                  if (file.empty ())
                    error ("echo: no such file %s", arg1.c_str ());

                  m_echo |= ECHO_FUNCTIONS;
                  m_echo_files[file] = true;
                }
            }
          else if (arg0 == "off")
            {
              if (arg1 == "all")
                {
                  m_echo = ECHO_OFF;
                  m_echo_files.clear ();
                }
              else
                {
                  std::string file = fcn_file_in_path (arg1);
                  file = sys::env::make_absolute (file);

                  if (file.empty ())
                    error ("echo: no such file %s", arg1.c_str ());

                  m_echo_files[file] = false;
                }
            }
          else
            print_usage ();
        }
        break;

      default:
        print_usage ();
        break;
      }

    if (cleanup_pushed)
      maybe_set_echo_state ();

    return octave_value ();
  }

  bool tree_evaluator::in_debug_repl (void) const
  {
    return (m_debugger_stack.empty ()
            ? false : m_debugger_stack.top()->in_debug_repl ());
  }

  void tree_evaluator::dbcont (void)
  {
    if (! m_debugger_stack.empty ())
      m_debugger_stack.top()->dbcont ();
  }

  void tree_evaluator::dbquit (bool all)
  {
    if (! m_debugger_stack.empty ())
      m_debugger_stack.top()->dbquit (all);
  }

  static octave_value end_value (const octave_value& value,
                                 octave_idx_type index_position,
                                 octave_idx_type num_indices)
  {
    dim_vector dv = value.dims ();
    int ndims = dv.ndims ();

    if (num_indices < ndims)
      {
        for (int i = num_indices; i < ndims; i++)
          dv(num_indices-1) *= dv(i);

        if (num_indices == 1)
          {
            ndims = 2;
            dv.resize (ndims);
            dv(1) = 1;
          }
        else
          {
            ndims = num_indices;
            dv.resize (ndims);
          }
      }

    return (index_position < ndims
            ? octave_value (dv(index_position)) : octave_value (1.0));
  }

  octave_value_list
  tree_evaluator::evaluate_end_expression (const octave_value_list& args)
  {
    int nargin = args.length ();

    if (nargin != 0 && nargin != 3)
      print_usage ();

    if (nargin == 3)
      {
        octave_idx_type index_position
          = args(1).xidx_type_value ("end: K must be integer value");

        if (index_position < 1)
          error ("end: K must be greater than zero");

        octave_idx_type num_indices
          = args(2).xidx_type_value ("end: N must be integer value");

        if (num_indices < 1)
          error ("end: N must be greater than zero");

        return end_value (args(0), index_position-1, num_indices);
      }

    // If m_indexed_object is undefined, then this use of 'end' is
    // either appearing in a function call argument list or in an
    // attempt to index an undefined symbol.  There seems to be no
    // reasonable way to provide a better error message.  So just fail
    // with an invalid use message.  See bug #58830.

    if (m_indexed_object.is_undefined ())
      error ("invalid use of 'end': may only be used to index existing value");

    octave_value expr_result;

    if (m_index_list.empty ())
      expr_result = m_indexed_object;
    else
      {
        try
          {
            // When evaluating "end" with no arguments, we should have
            // been called from the built-in Fend function that appears
            // in the context of an argument list.  Fend will be
            // evaluated in its own stack frame.  But we need to
            // evaluate the partial expression that the special "end"
            // token applies to in the calling stack frame.

            unwind_action act ([=] (std::size_t frm)
                               {
                                 m_call_stack.restore_frame (frm);
                               }, m_call_stack.current_frame ());

            std::size_t n = m_call_stack.find_current_user_frame ();
            m_call_stack.goto_frame (n);

            // End is only valid inside argument lists used for
            // indexing.  The dispatch class is set by the function that
            // evaluates the argument list.

            // Silently ignore extra output values.

            octave_value_list tmp
              = m_indexed_object.subsref (m_index_type, m_index_list, 1);

            expr_result = tmp.length () ? tmp(0) : octave_value ();

            if (expr_result.is_cs_list ())
              err_indexed_cs_list ();
          }
        catch (const index_exception&)
          {
            error ("error evaluating partial expression for END");
          }
      }

    if (expr_result.isobject ())
      {
        // FIXME: is there a better way to lookup and execute a method
        // that handles all the details like setting the dispatch class
        // appropriately?

        std::string dispatch_class = expr_result.class_name ();

        symbol_table& symtab = m_interpreter.get_symbol_table ();

        octave_value meth = symtab.find_method ("end", dispatch_class);

        if (meth.is_defined ())
          return m_interpreter.feval
            (meth, ovl (expr_result, m_index_position+1, m_num_indices), 1);
      }

    return end_value (expr_result, m_index_position, m_num_indices);
  }

  octave_value
  tree_evaluator::PS4 (const octave_value_list& args, int nargout)
  {
    return set_internal_variable (m_PS4, args, nargout, "PS4");
  }

  bool tree_evaluator::echo_this_file (const std::string& file, int type) const
  {
    if ((type & m_echo) == ECHO_SCRIPTS)
      {
        // Asking about scripts and echo is enabled for them.
        return true;
      }

    if ((type & m_echo) == ECHO_FUNCTIONS)
      {
        // Asking about functions and echo is enabled for functions.
        // Now, which ones?

        auto p = m_echo_files.find (file);

        if (m_echo & ECHO_ALL)
          {
            // Return true ulness echo was turned off for a specific
            // file.

            return (p == m_echo_files.end () || p->second);
          }
        else
          {
            // Return true if echo is specifically enabled for this file.

            return p != m_echo_files.end () && p->second;
          }
      }

    return false;
  }

  void tree_evaluator::echo_code (int line)
  {
    std::string prefix = command_editor::decode_prompt_string (m_PS4);

    octave_function *curr_fcn = m_call_stack.current_function ();

    if (curr_fcn && curr_fcn->is_user_code ())
      {
        octave_user_code *code = dynamic_cast<octave_user_code *> (curr_fcn);

        int num_lines = line - m_echo_file_pos + 1;

        std::deque<std::string> lines
          = code->get_code_lines (m_echo_file_pos, num_lines);

        for (auto& elt : lines)
          octave_stdout << prefix << elt << std::endl;
      }
  }

  // Decide if it's time to quit a for or while loop.
  bool tree_evaluator::quit_loop_now (void)
  {
    octave_quit ();

    // Maybe handle 'continue N' someday...

    if (m_continuing)
      m_continuing--;

    bool quit = (m_returning || m_breaking || m_continuing);

    if (m_breaking)
      m_breaking--;

    return quit;
  }

  void tree_evaluator::bind_auto_fcn_vars (const string_vector& arg_names,
                                           const Matrix& ignored_outputs,
                                           int nargin, int nargout,
                                           bool takes_varargs,
                                           const octave_value_list& va_args)
  {
    set_auto_fcn_var (stack_frame::ARG_NAMES, Cell (arg_names));
    set_auto_fcn_var (stack_frame::IGNORED, ignored_outputs);
    set_auto_fcn_var (stack_frame::NARGIN, nargin);
    set_auto_fcn_var (stack_frame::NARGOUT, nargout);
    set_auto_fcn_var (stack_frame::SAVED_WARNING_STATES, octave_value ());

    if (takes_varargs)
      assign ("varargin", va_args.cell_value ());
  }

  std::string
  tree_evaluator::check_autoload_file (const std::string& nm) const
  {
    if (sys::env::absolute_pathname (nm))
      return nm;

    std::string full_name = nm;

    octave_user_code *fcn = m_call_stack.current_user_code ();

    bool found = false;

    if (fcn)
      {
        std::string fname = fcn->fcn_file_name ();

        if (! fname.empty ())
          {
            fname = sys::env::make_absolute (fname);
            fname = fname.substr (0, fname.find_last_of (sys::file_ops::dir_sep_str ()) + 1);

            sys::file_stat fs (fname + nm);

            if (fs.exists ())
              {
                full_name = fname + nm;
                found = true;
              }
          }
      }

    if (! found)
      warning_with_id ("Octave:autoload-relative-file-name",
                       "autoload: '%s' is not an absolute filename",
                       nm.c_str ());

    return full_name;
  }

DEFMETHOD (max_recursion_depth, interp, args, nargout,
           doc: /* -*- texinfo -*-
@deftypefn  {} {@var{val} =} max_recursion_depth ()
@deftypefnx {} {@var{old_val} =} max_recursion_depth (@var{new_val})
@deftypefnx {} {@var{old_val} =} max_recursion_depth (@var{new_val}, "local")
Query or set the internal limit on the number of times a function may
be called recursively.

If the limit is exceeded, an error message is printed and control returns to
the top level.

When called from inside a function with the @qcode{"local"} option, the
variable is changed locally for the function and any subroutines it calls.
The original variable value is restored when exiting the function.

@seealso{max_stack_depth}
@end deftypefn */)
{
  tree_evaluator& tw = interp.get_evaluator ();

  return tw.max_recursion_depth (args, nargout);
}

/*
%!test
%! orig_val = max_recursion_depth ();
%! old_val = max_recursion_depth (2*orig_val);
%! assert (orig_val, old_val);
%! assert (max_recursion_depth (), 2*orig_val);
%! max_recursion_depth (orig_val);
%! assert (max_recursion_depth (), orig_val);

%!error max_recursion_depth (1, 2)
*/

DEFMETHOD (whos_line_format, interp, args, nargout,
           doc: /* -*- texinfo -*-
@deftypefn  {} {@var{val} =} whos_line_format ()
@deftypefnx {} {@var{old_val} =} whos_line_format (@var{new_val})
@deftypefnx {} {@var{old_val} =} whos_line_format (@var{new_val}, "local")
Query or set the format string used by the command @code{whos}.

A full format string is:
@c Set example in small font to prevent overfull line

@smallexample
%[modifier]<command>[:width[:left-min[:balance]]];
@end smallexample

The following command sequences are available:

@table @code
@item %a
Prints attributes of variables (c=complex, s=sparse, f=formal parameter,
g=global, p=persistent).

@item %b
Prints number of bytes occupied by variables.

@item %c
Prints class names of variables.

@item %e
Prints elements held by variables.

@item %n
Prints variable names.

@item %s
Prints dimensions of variables.

@item %t
Prints type names of variables.
@end table

Every command may also have an alignment modifier:

@table @code
@item l
Left alignment.

@item r
Right alignment (default).

@item c
Column-aligned (only applicable to command %s).
@end table

The @code{width} parameter is a positive integer specifying the minimum
number of columns used for printing.  No maximum is needed as the field will
auto-expand as required.

The parameters @code{left-min} and @code{balance} are only available when
the column-aligned modifier is used with the command @samp{%s}.
@code{balance} specifies the column number within the field width which
will be aligned between entries.  Numbering starts from 0 which indicates
the leftmost column.  @code{left-min} specifies the minimum field width to
the left of the specified balance column.

The default format is:

@example
"  %la:5; %ln:6; %cs:16:6:1;  %rb:12;  %lc:-1;@backslashchar{}n"
@end example

When called from inside a function with the @qcode{"local"} option, the
variable is changed locally for the function and any subroutines it calls.
The original variable value is restored when exiting the function.
@seealso{whos}
@end deftypefn */)
{
  tree_evaluator& tw = interp.get_evaluator ();

  return tw.whos_line_format (args, nargout);
}

DEFMETHOD (silent_functions, interp, args, nargout,
           doc: /* -*- texinfo -*-
@deftypefn  {} {@var{val} =} silent_functions ()
@deftypefnx {} {@var{old_val} =} silent_functions (@var{new_val})
@deftypefnx {} {@var{old_val} =} silent_functions (@var{new_val}, "local")
Query or set the internal variable that controls whether internal
output from a function is suppressed.

If this option is disabled, Octave will display the results produced by
evaluating expressions within a function body that are not terminated with
a semicolon.

When called from inside a function with the @qcode{"local"} option, the
variable is changed locally for the function and any subroutines it calls.
The original variable value is restored when exiting the function.
@end deftypefn */)
{
  tree_evaluator& tw = interp.get_evaluator ();

  return tw.silent_functions (args, nargout);
}

/*
%!test
%! orig_val = silent_functions ();
%! old_val = silent_functions (! orig_val);
%! assert (orig_val, old_val);
%! assert (silent_functions (), ! orig_val);
%! silent_functions (orig_val);
%! assert (silent_functions (), orig_val);

%!error silent_functions (1, 2)
*/

DEFMETHOD (string_fill_char, interp, args, nargout,
           doc: /* -*- texinfo -*-
@deftypefn  {} {@var{val} =} string_fill_char ()
@deftypefnx {} {@var{old_val} =} string_fill_char (@var{new_val})
@deftypefnx {} {@var{old_val} =} string_fill_char (@var{new_val}, "local")
Query or set the internal variable used to pad all rows of a character
matrix to the same length.

The value must be a single character and the default is @qcode{" "} (a
single space).  For example:

@example
@group
string_fill_char ("X");
[ "these"; "are"; "strings" ]
      @result{}  "theseXX"
          "areXXXX"
          "strings"
@end group
@end example

When called from inside a function with the @qcode{"local"} option, the
variable is changed locally for the function and any subroutines it calls.
The original variable value is restored when exiting the function.
@end deftypefn */)
{
  tree_evaluator& tw = interp.get_evaluator ();

  return tw.string_fill_char (args, nargout);
}

/*
## string_fill_char() function call must be outside of %!test block
## due to the way a %!test block is wrapped inside a function
%!shared orig_val, old_val
%! orig_val = string_fill_char ();
%! old_val  = string_fill_char ("X");
%!test
%! assert (orig_val, old_val);
%! assert (string_fill_char (), "X");
%! assert (["these"; "are"; "strings"], ["theseXX"; "areXXXX"; "strings"]);
%! string_fill_char (orig_val);
%! assert (string_fill_char (), orig_val);

%!assert ( [ [], {1} ], {1} )

%!error string_fill_char (1, 2)
*/

DEFMETHOD (PS4, interp, args, nargout,
           doc: /* -*- texinfo -*-
@deftypefn  {} {@var{val} =} PS4 ()
@deftypefnx {} {@var{old_val} =} PS4 (@var{new_val})
@deftypefnx {} {@var{old_val} =} PS4 (@var{new_val}, "local")
Query or set the character string used to prefix output produced
when echoing commands is enabled.

The default value is @qcode{"+ "}.
@xref{Diary and Echo Commands}, for a description of echoing commands.

When called from inside a function with the @qcode{"local"} option, the
variable is changed locally for the function and any subroutines it calls.
The original variable value is restored when exiting the function.
@seealso{echo, PS1, PS2}
@end deftypefn */)
{
  tree_evaluator& tw = interp.get_evaluator ();

  return tw.PS4 (args, nargout);
}

DEFMETHOD (echo, interp, args, nargout,
           doc: /* -*- texinfo -*-
@deftypefn  {} {} echo
@deftypefnx {} {} echo on
@deftypefnx {} {} echo off
@deftypefnx {} {} echo on all
@deftypefnx {} {} echo off all
@deftypefnx {} {} echo @var{function} on
@deftypefnx {} {} echo @var{function} off
Control whether commands are displayed as they are executed.

Valid options are:

@table @code
@item on
Enable echoing of commands as they are executed in script files.

@item off
Disable echoing of commands as they are executed in script files.

@item on all
Enable echoing of commands as they are executed in script files and
functions.

@item off all
Disable echoing of commands as they are executed in script files and
functions.

@item @var{function} on
Enable echoing of commands as they are executed in the named function.

@item @var{function} off
Disable echoing of commands as they are executed in the named function.
@end table

@noindent
With no arguments, @code{echo} toggles the current echo state.

@seealso{PS4}
@end deftypefn */)
{
  tree_evaluator& tw = interp.get_evaluator ();

  return tw.echo (args, nargout);
}

/*
%!error echo ([])
%!error echo (0)
%!error echo ("")
%!error echo ("Octave")
%!error echo ("off", "invalid")
%!error echo ("on", "invalid")
%!error echo ("on", "all", "all")
*/

OCTAVE_END_NAMESPACE(octave)