--- freem/src/mdebug.c	2025/03/09 15:20:18	1.2
+++ freem/src/mdebug.c	2025/04/29 18:46:17	1.5
@@ -1,23 +1,11 @@
 /*
- *                            *
- *                           * *
- *                          *   *
- *                     ***************
- *                      * *       * *
- *                       *  MUMPS  *
- *                      * *       * *
- *                     ***************
- *                          *   *
- *                           * *
- *                            *
- *
- *   mdebug.c
+ *   $Id: mdebug.c,v 1.5 2025/04/29 18:46:17 snw Exp $
  *    debugger enhancements
  *
  *  
  *   Author: Serena Willis <snw@coherent-logic.com>
  *    Copyright (C) 1998 MUG Deutschland
- *    Copyright (C) 2020 Coherent Logic Development LLC
+ *    Copyright (C) 2020, 2025 Coherent Logic Development LLC
  *
  *
  *   This file is part of FreeM.
@@ -35,11 +23,54 @@
  *   You should have received a copy of the GNU Affero Public License
  *   along with FreeM.  If not, see <https://www.gnu.org/licenses/>.
  *
+ *   $Log: mdebug.c,v $
+ *   Revision 1.5  2025/04/29 18:46:17  snw
+ *   Begin work on interactive debugger
+ *
+ *   Revision 1.4  2025/04/28 19:38:55  snw
+ *   Add trace mode
+ *
+ *   Revision 1.3  2025/03/09 19:50:47  snw
+ *   Second phase of REUSE compliance and header reformat
+ *
+ *
+ * SPDX-FileCopyrightText:  (C) 2025 Coherent Logic Development LLC
+ * SPDX-License-Identifier: AGPL-3.0-or-later
  **/
 
 #include <stdio.h>
 #include <stdlib.h>
 #include <string.h>
+#include <unistd.h>
+
+#include "config.h"
+
+#ifdef HAVE_LIBREADLINE
+#  if defined(HAVE_READLINE_READLINE_H)
+#    include <readline/readline.h>
+#  elif defined(HAVE_READLINE_H)
+#    include <readline.h>
+#  else /* !defined(HAVE_READLINE_H) */
+extern char *readline ();
+#  endif /* !defined(HAVE_READLINE_H) */
+/*char *cmdline = NULL;*/
+#else /* !defined(HAVE_READLINE_READLINE_H) */
+  /* no readline */
+#endif /* HAVE_LIBREADLINE */
+
+#ifdef HAVE_READLINE_HISTORY
+#  if defined(HAVE_READLINE_HISTORY_H)
+#    include <readline/history.h>
+#  elif defined(HAVE_HISTORY_H)
+#    include <history.h>
+#  else /* !defined(HAVE_HISTORY_H) */
+extern void add_history ();
+extern int write_history ();
+extern int read_history ();
+#  endif /* defined(HAVE_READLINE_HISTORY_H) */
+  /* no history */
+#endif /* HAVE_READLINE_HISTORY */
+
 
 #include "mpsdef.h"
 #include "mdebug.h"
@@ -67,6 +98,56 @@ void dbg_init (void)
 
 }
 
+int debugger (void)
+{
+    
+#if defined(HAVE_LIBREADLINE)    
+    static int first_entry = TRUE;
+    char *dbg_buf;
+    char dbg_prompt[256];
+    HIST_ENTRY **dbg_hist;
+    int dbg_hist_idx;
+    HIST_ENTRY *dbg_hist_ent;
+    char rouname_buf[256];
+    
+    set_io (UNIX);
+    
+    if (first_entry) {
+        first_entry = FALSE;
+        
+        printf ("\nEntering debug mode; M commands unavailable.\n");
+        printf ("Type 'exit' to return to direct mode; 'help' for help.\n\n");
+    }
+
+    while (1) {
+        stcpy (rouname_buf, rou_name);
+        stcnv_m2c (rouname_buf);
+        
+        snprintf (dbg_prompt, sizeof (dbg_prompt) - 1, "%s $STACK=%d [DEBUG]> ", rouname_buf, nstx);
+
+        dbg_buf = readline (dbg_prompt);
+
+        if (!dbg_buf) continue;
+
+        if (strcmp (dbg_buf, "exit") == 0) {
+            first_entry = TRUE;
+            printf ("\n\nExiting debug mode.\n\n");
+            set_io (MUMPS);
+            return FALSE;
+        }
+        else {
+            printf ("DEBUG:  invalid command\r\n");
+        }
+        
+    }
+
+    return TRUE;
+#else
+    return FALSE;
+#endif
+
+}
+
 dbg_watch *dbg_add_watch (char *varnam)
 {
     register int i;
@@ -243,5 +324,5 @@ void dbg_fire_watch (char *varnam) {
 	w->chgct++;
 	w->firect++;
 	dbg_pending_watches++;
-
+        
 }