Index: generic/nsfShadow.c
===================================================================
diff -u -r880487204ff2da18d2d25ebd727b9b4bbda86c8e -rdb831678bc92ce4e39bf4ff303f32491a3c4f9d9
--- generic/nsfShadow.c	(.../nsfShadow.c)	(revision 880487204ff2da18d2d25ebd727b9b4bbda86c8e)
+++ generic/nsfShadow.c	(.../nsfShadow.c)	(revision db831678bc92ce4e39bf4ff303f32491a3c4f9d9)
@@ -4,7 +4,7 @@
  *      API support for shadowing (overloading) and accessing C-implemented
  *      Tcl obj-commands.
  *  
- *  Copyright (C) 1999-2013 Gustaf Neumann
+ *  Copyright (C) 1999-2014 Gustaf Neumann
  *
  * Permission is hereby granted, free of charge, to any person obtaining a
  * copy of this software and associated documentation files (the "Software"),
@@ -44,12 +44,16 @@
  *
  *----------------------------------------------------------------------
  */
+static int NsfReplaceCommandCleanup(Tcl_Interp *interp, NsfGlobalNames name) nonnull(1);
+
 static int
 NsfReplaceCommandCleanup(Tcl_Interp *interp, NsfGlobalNames name) {
   Tcl_Command cmd;
   int result = TCL_OK;
   NsfShadowTclCommandInfo *ti = &RUNTIME_STATE(interp)->tclCommands[name-NSF_EXPR];
 
+  assert(interp);
+
   /*fprintf(stderr," cleanup for %s  ti=%p in %p\n", NsfGlobalStrings[name], ti, interp);*/
   cmd = Tcl_GetCommandFromObj(interp, NsfGlobalObjs[name]);
   if (cmd != NULL) {
@@ -77,10 +81,16 @@
  *
  *----------------------------------------------------------------------
  */
+static void NsfReplaceCommandCheck(Tcl_Interp *interp, NsfGlobalNames name, Tcl_ObjCmdProc *proc) nonnull(1) nonnull(3);
+
 static void
 NsfReplaceCommandCheck(Tcl_Interp *interp, NsfGlobalNames name, Tcl_ObjCmdProc *proc) {
-  Tcl_Command cmd;
   NsfShadowTclCommandInfo *ti = &RUNTIME_STATE(interp)->tclCommands[name-NSF_EXPR];
+  Tcl_Command cmd;
+
+  assert(interp);
+  assert(proc);
+
   cmd = Tcl_GetCommandFromObj(interp, NsfGlobalObjs[name]);
   
   if (cmd != NULL && ti->proc && Tcl_Command_objProc(cmd) != proc) {
@@ -110,13 +120,18 @@
  *
  *----------------------------------------------------------------------
  */
+static int NsfReplaceCommand(Tcl_Interp *interp, NsfGlobalNames name,
+			     Tcl_ObjCmdProc *nsfReplacementProc, int pass) nonnull(1);
+
 static int
 NsfReplaceCommand(Tcl_Interp *interp, NsfGlobalNames name,
 		    Tcl_ObjCmdProc *nsfReplacementProc, int pass) {
   Tcl_Command cmd;
   NsfShadowTclCommandInfo *ti = &RUNTIME_STATE(interp)->tclCommands[name-NSF_EXPR];
   int result = TCL_OK;
 
+  assert(interp);
+
   /*fprintf(stderr,"NsfReplaceCommand %d\n", name);*/
   cmd = Tcl_GetCommandFromObj(interp, NsfGlobalObjs[name]);
   
@@ -162,13 +177,16 @@
  *
  *----------------------------------------------------------------------
  */
-EXTERN int
-NsfProcStub(ClientData clientData, Tcl_Interp *interp, int objc, Tcl_Obj *CONST objv[]);
+EXTERN int NsfProcStub(ClientData clientData, Tcl_Interp *interp, int objc, Tcl_Obj *CONST objv[]) 
+  nonnull(1) nonnull(2) nonnull(4);
 
 static int
 Nsf_InfoBodyObjCmd(ClientData clientData, Tcl_Interp *interp, int objc, Tcl_Obj *CONST objv[]) {
   Tcl_Command cmd;
 
+  assert(interp);
+  assert(objv); 
+
   if (objc != 2) {
     /* wrong # args, let Tcl generate the error */
     return NsfCallCommand(interp, NSF_INFO_BODY, objc, objv);
@@ -369,8 +387,11 @@
 int
 NsfShadowTclCommands(Tcl_Interp *interp, NsfShadowOperations load) {
   int rc = TCL_OK;
+  assert(interp);
+
   if (load == SHADOW_LOAD) {
     int initialized = (RUNTIME_STATE(interp)->tclCommands != NULL);
+
     assert(initialized == 0);
     RUNTIME_STATE(interp)->tclCommands = 
       NEW_ARRAY(NsfShadowTclCommandInfo, NSF_RENAME - NSF_EXPR + 1);
@@ -385,7 +406,7 @@
 #endif
     rc |= NsfReplaceCommand(interp, NSF_FORMAT,     NULL, initialized);
     rc |= NsfReplaceCommand(interp, NSF_INTERP,     NULL, initialized);
-    rc |= NsfReplaceCommand(interp, NSF_IS,         NULL, initialized);
+    rc |= NsfReplaceCommand(interp, NSF_STRING_IS,  NULL, initialized);
 
     /* for the following commands, we have to add our own semantics */
     rc |= NsfReplaceCommand(interp, NSF_INFO_BODY,  Nsf_InfoBodyObjCmd, initialized);