--- a/gui-main.cpp	Wed May 22 17:30:46 2019 -0400
+++ b/gui-main.cpp	Wed May 22 18:07:37 2019 -0400
@@ -23,15 +23,79 @@
 
 namespace gui
 {
-  int available_char = 0;
+  static int available_char = 0;
 
-  command_window *calc_interaction_window = 0;
+  static command_window *calc_interaction_window = 0;
 
   static inline int ctrl (int c)
   {
     return c & 0x1f;
   }
 
+  static int getc (FILE *)
+  {
+    int tmp = available_char;
+    available_char = 0;
+    return tmp;
+  }
+
+  static void redisplay (void)
+  {
+    if (calc_interaction_window)
+      calc_interaction_window->redisplay ();
+  }
+
+  static void prep_term (int)
+  {
+  }
+
+  static void deprep_term (void)
+  {
+  }
+
+  static void accept_line (char *line)
+  {
+    if (calc_interaction_window)
+      calc_interaction_window->accept_line (line ? line : "");
+  }
+
+  static void display_completion_matches (char **matches, int num_matches,
+                                          int /* max_length */)
+  {
+    if (calc_interaction_window)
+      {
+        std::ostringstream buf;
+
+        if (num_matches > 1)
+          buf << "\n";
+
+        for (int i = 1; i < num_matches; i++)
+          buf << matches[i] << "\n";
+
+        calc_interaction_window->insert_at_end (buf.str ());
+
+        calc_interaction_window->redisplay ();
+      }
+  }
+
+  static void readline_init (void)
+  {
+    rl_initialize ();
+
+    rl_getc_function = getc;
+    rl_redisplay_function = redisplay;
+    rl_prep_term_function = prep_term;
+    rl_deprep_term_function = deprep_term;
+    rl_completion_display_matches_hook = display_completion_matches;
+
+    rl_callback_handler_install (">> ", accept_line);
+  }
+
+  static void readline_fini (void)
+  {
+    rl_callback_handler_remove ();
+  }
+
   command_window::command_window (QWidget *p)
     : QTextEdit (p),
       m_buffer (new QTextDocument ()),
@@ -50,6 +114,9 @@
     connect (this, SIGNAL (input_char_available (int)),
              this, SLOT (handle_input_char (int)));
 
+    connect (this, SIGNAL (accept_line_signal (const QString&)),
+             m_interpreter, SLOT (accept_input_line (const QString&)));
+
     insert_at_end
       ("Qt Example Calculator.\n"
        "Available operations: + - * / ^ ()\n"
@@ -66,7 +133,7 @@
 
   // Accept an input line, parse and possibly execute it.
 
-  void command_window::accept (const std::string& line)
+  void command_window::accept_line (const std::string& line)
   {
     if (calc::debug_mode)
       std::cerr << "accept: " << line << std::endl;
@@ -78,9 +145,7 @@
         add_history (line.c_str ());
         using_history ();
 
-        // FIXME: what is the right thing to do with status returned
-        // by parser.
-        interpreter::parse_and_execute (line);
+        emit accept_line_signal (QString::fromStdString (line));
       }
   }
 
@@ -318,8 +383,12 @@
 
     calc_interaction_window->show ();
 
+    readline_init ();
+
     int status = app.exec ();
 
+    readline_fini ();
+
     return status;
   }