Index: generic/nsf.c
===================================================================
diff -u -r14101af0c3253e79cf68622cb05e51eb780e1f39 -r99c15f26c1fbcfb35c4d7557773fea8af63e89a6
--- generic/nsf.c	(.../nsf.c)	(revision 14101af0c3253e79cf68622cb05e51eb780e1f39)
+++ generic/nsf.c	(.../nsf.c)	(revision 99c15f26c1fbcfb35c4d7557773fea8af63e89a6)
@@ -9582,9 +9582,55 @@
     cscPtr->objc = objc;
     cscPtr->objv = (Tcl_Obj **)objv;
 
+
     if (likely(result == TCL_OK)) {
+
+      if ((((Command *)cmdPtr)->flags & CMD_HAS_EXEC_TRACES)) {
+	int i;
+	Nsf_Param *paramPtr;
+	Tcl_Obj *argNameObjs = Tcl_NewListObj(0, NULL);
+	Tcl_Obj *argValueObjs = Tcl_NewListObj(0, NULL);
+	Tcl_Obj *argObjs = Tcl_NewListObj(2, NULL);
+	Tcl_Obj *traceObjv[3];
+
+	/* numArgs = framePtr->procPtr->numArgs;
+	argObjs = (Tcl_Obj **) TclStackAlloc(interp,
+	(int) sizeof(Tcl_Obj *) * (numArgs+1));*/
+	
+	for (i = 1, paramPtr = paramDefs->paramsPtr; paramPtr->name; paramPtr++, i++) {
+	  if(pcPtr->full_objv[i] != NsfGlobalObjs[NSF___UNKNOWN__]) {
+	    Tcl_ListObjAppendElement(interp, argValueObjs, pcPtr->full_objv[i]);
+	    Tcl_ListObjAppendElement(interp, argNameObjs, paramPtr->nameObj);
+	  }
+	}
+	
+	traceObjv[0] = object->cmdName;
+	traceObjv[1] = objv[0];
+
+	Tcl_ListObjAppendElement(interp, argObjs, argNameObjs);
+	Tcl_ListObjAppendElement(interp, argObjs, argValueObjs);
+
+	INCR_REF_COUNT(argObjs);
+	traceObjv[2] = argObjs;
+	if((result = TclCheckExecutionTraces(interp, 
+					     Tcl_GetCommandName(interp, cmdPtr), 
+					     strlen(Tcl_GetCommandName(interp,cmdPtr)),
+					     (Command *)cmdPtr, 
+					     result, 
+					     TCL_TRACE_ENTER_EXEC, 
+					     3, traceObjv)) == TCL_ERROR) {
+	  /* Some error handling needed? */
+	  DECR_REF_COUNT(argObjs);
+	  goto prep_done;
+	}
+	DECR_REF_COUNT(argObjs);
+      }
+
       releasePc = 1;
-      result = PushProcCallFrame(cp, interp, pcPtr->objc+1, pcPtr->full_objv, cscPtr);
+      result = PushProcCallFrame(cp, interp, pcPtr->objc+1, pcPtr->full_objv, cscPtr); 
+
+      
+
     } else {
       /*
        * some error occurred
Index: tests/rac.test
===================================================================
diff -u -r14101af0c3253e79cf68622cb05e51eb780e1f39 -r99c15f26c1fbcfb35c4d7557773fea8af63e89a6
--- tests/rac.test	(.../rac.test)	(revision 14101af0c3253e79cf68622cb05e51eb780e1f39)
+++ tests/rac.test	(.../rac.test)	(revision 99c15f26c1fbcfb35c4d7557773fea8af63e89a6)
@@ -13,117 +13,119 @@
 
 package require nx::test
 
-nx::Class create Sensor {
-  :property -accessor public {value:integer 1}
-}
+nx::test case existing-impl {
 
-set invar [list {[regexp {^[0-9]$} ${:value}] == 1}]
-
-::nsf::method::assertion Sensor class-invar $invar
-
-? {::nsf::method::assertion Sensor class-invar} $invar
-
-#
-# Minimal object interface to ::nsf::method::assertion
-#
-
-#
-# TODO: This should not be ::nx::VariableSlot below, but
-# ::nx::ObjectParameterSlot mixes alias + slotassign.
-#
-
-::nx::VariableSlot create ::nx::Object::slot::object-invariant {
-  :public object method get {obj prop} {
-    ::nsf::method::assertion $obj object-invar
+  nx::Class create Sensor {
+    :property -accessor public {value:integer 1}
   }
-
-  :public object method assign {obj prop value} {
-    ::nsf::method::assertion $obj object-invar $value
+  
+  set ::invar [list {[regexp {^[0-9]$} ${:value}] == 1}]
+  
+  ::nsf::method::assertion Sensor class-invar $::invar
+  
+  ? {::nsf::method::assertion Sensor class-invar} $::invar
+  
+  #
+  # Minimal object interface to ::nsf::method::assertion
+  #
+  
+  #
+  # TODO: This should not be ::nx::VariableSlot below, but
+  # ::nx::ObjectParameterSlot mixes alias + slotassign.
+  #
+  
+  ::nx::VariableSlot create ::nx::Object::slot::object-invariant {
+    :public object method get {obj prop} {
+      ::nsf::method::assertion $obj object-invar
+    }
+    
+    :public object method assign {obj prop value} {
+      ::nsf::method::assertion $obj object-invar $value
+    }
   }
-}
-
-::nx::VariableSlot create ::nx::Class::slot::invariant {
-  :public object method get {cls prop} {
-    ::nsf::method::assertion $cls class-invar
+  
+  ::nx::VariableSlot create ::nx::Class::slot::invariant {
+    :public object method get {cls prop} {
+      ::nsf::method::assertion $cls class-invar
+    }
+    
+    :public object method assign {cls prop value} {
+      ::nsf::method::assertion $cls class-invar $value
+    }
   }
-
-  :public object method assign {cls prop value} {
-    ::nsf::method::assertion $cls class-invar $value
+  
+  ? {Sensor cget -invariant} $::invar 
+  
+  ? {::nsf::method::assertion Sensor class-invar} $::invar
+  
+  ? {Sensor configure -invariant ""} ""
+  
+  ? {Sensor cget -invariant} ""
+  
+  ? {::nsf::method::assertion Sensor class-invar} ""
+  
+  ? {Sensor configure -invariant $::invar} ""
+  
+  ? {Sensor cget -invariant} $::invar 
+  
+  ? {::nsf::method::assertion Sensor class-invar} $::invar
+  
+  Sensor create s1
+  
+  ? {s1 cget -object-invariant} ""
+  
+  ? {s1 configure -object-invariant $::invar} ""
+  
+  ? {s1 cget -object-invariant} $::invar
+  
+  ? {s1 configure -object-invariant ""} ""
+  
+  
+  #
+  # TODO: re-position -pre-condition, to appear before the method
+  # body. This would ease reading.
+  #
+  #
+  # TODO: Why is there a firm requirement to provide a post-condition,
+  # when defining a pre-condition (they are non-positional
+  # parameters in NX)?
+  #
+  # --> because of XOTcl2 legacy interface? 
+  # i.e.: precondition:optional postcondition:optional
+  #
+  
+  
+  Sensor public method incrValue {} {
+    incr :value
+  } -precondition {
+    {[llength [set ::ARGS [nsf::current args]]]}
+    {# pre-condition:} 
+    {${:value} > 0}
+  } -postcondition {
+    {[puts stderr POST=${:value}] eq ""}
+    {# post-condition:} 
+    {${:value} > 1}
   }
-}
 
-? {Sensor cget -invariant} $invar 
-
-? {::nsf::method::assertion Sensor class-invar} $invar
-
-? {Sensor configure -invariant ""} ""
-
-? {Sensor cget -invariant} ""
-
-? {::nsf::method::assertion Sensor class-invar} ""
-
-? {Sensor configure -invariant $invar} ""
-
-? {Sensor cget -invariant} $invar 
-
-? {::nsf::method::assertion Sensor class-invar} $invar
-
-Sensor create s1
-
-? {s1 cget -object-invariant} ""
-
-? {s1 configure -object-invariant $invar} ""
-
-? {s1 cget -object-invariant} $invar
-
-? {s1 configure -object-invariant ""} ""
-
-
-#
-# TODO: re-position -pre-condition, to appear before the method
-# body. This would ease reading.
-#
-#
-# TODO: Why is there a firm requirement to provide a post-condition,
-# when defining a pre-condition (they are non-positional
-# parameters in NX)?
-#
-# --> because of XOTcl2 legacy interface? 
-# i.e.: precondition:optional postcondition:optional
-#
-
-
-Sensor public method incrValue {} {
-  incr :value
-} -precondition {
-  {[set ::ARGS [nsf::current args]] eq "run {bar 1 2 3}"}
-  {# pre-condition:} 
-  {${:value} > 0}
-} -postcondition {
-  {[puts stderr POST=${:value}] eq ""}
-  {# post-condition:} 
-  {${:value} > 1}
+  proc bar args {
+    s1 incrValue
   }
+      
+      
+  #
+  # TODO: How to activate, deactivate RAC per object? Re-introduce check() method?
+  #
 
-proc bar args {
-  s1 incrValue
-}
+  # s1 check pre
+  ::nsf::method::assertion s1 check pre
 
+  ? {bar 1 2 3} "2"
 
-#
-# TODO: How to activate, deactivate RAC per object? Re-introduce check() method?
-#
+  #
+  # TODO: ::nsf::current jumps the call stack, picks an arbitrary call
+  # frame if the context provides for it.
+  #
 
-# s1 check pre
-::nsf::method::assertion s1 check pre
-
-? {bar 1 2 3} "2"
-
-#
-# TODO: ::nsf::current jumps the call stack, picks an arbitrary call
-# frame if the context provides for it.
-#
-
 ? {info exists ::ARGS} 1
 ? {set ::ARGS} "run {bar 1 2 3}" 
 
@@ -133,9 +135,11 @@
 #
 
 catch {s1 incrValue} ::msg
-? {set ::msg} {error in Assertion: {[set ::ARGS [nsf::current args]] eq "run {bar 1 2 3}"} in proc 'incrValue'
-can't find proc}
+? {set ::msg} {assertion failed check: {[llength [set ::ARGS [nsf::current args]]]} in proc 'incrValue'}
 
+# NOTE: at top level "::", this yields "can't find proc" because
+# [current args] is situated in an obj frame ...
+
 ? {s1 value -1} -1
 ? {s1 value 10} 10
 
@@ -521,3 +525,72 @@
 
 ::nsf::method::assertion z1 check {}
 
+}
+
+
+nx::test case trace-impl {
+
+  # / / / / / / / / / / / / / / / / / / / / / / / / / /
+  # Towards a minimal RAC implementation using [trace]
+  #
+
+  nx::Class create S {
+    :public method foo {a:integer b c:optional} {
+      puts stderr FOO
+    } 
+  }
+
+  # -precondition {
+  #  {[llength [[:info class] eval [list lappend :TRACE "::S-foo-PRE"]]]}
+  # }
+
+  set precond {$a == 1 && ![info exists :z] && [puts stderr ****[info vars],${:z}] eq ""}
+
+  # set enterCmdPrefix [list apply {{assertion localVars call ops} {
+
+  #   set argv [lassign $call mh]
+  #   lassign $argv {*}$localVars
+    
+  #   ::nsf::__db_show_stack
+  #   puts stderr >>>>>>>>[uplevel 1 [list current args]]
+  #   puts stderr +++++++++++[expr $assertion][info vars]
+  #   puts stderr --localVars=$localVars,call=$call,ops=$ops,[info vars],[info locals]; puts stderr SELF=[current]
+  #   if {![expr $assertion]} {
+  #     return -code error "Run-time assertion check failed."
+  #   }}} $precond [S info method args foo]]
+
+  proc assert {assertion call ops} {
+    # ::nsf::__db_show_stack
+    lassign $call obj mh argv
+    set cmd [list ::apply [list [lindex $argv 0] [list expr $assertion]] {*}[lindex $argv 1]]
+    puts stderr cmd=$cmd
+    set r [$obj eval $cmd]
+    if {!$r} {
+      return -code error "Run-time assertion check failed."
+    }
+  }
+
+  set enterCmdPrefix [list assert $precond]
+
+  puts stderr enterCmdPrefix=$enterCmdPrefix
+
+  ::trace add execution [S info method handle foo] enter $enterCmdPrefix
+
+  # -postcondition {
+  #  {[llength [[:info class] eval [list lappend :TRACE "::S-foo-POST"]]]}
+  # }
+
+  ::trace add execution [S info method handle foo] leave $enterCmdPrefix
+
+  puts stderr >>>>[S info methods],[S info method args foo]
+
+  S create s1 {
+    set :z YYY
+  }
+  puts stderr [s1 [S info method handle foo] 1 2]
+
+  # 1) Why are the execution traces not fired upon method execution, only direct cmd calls?
+  # 2) How does the trace dispatcher obtain the unfolded argument vector?
+  # 3) How can I provide the object context to enter/leave traces?
+
+}
\ No newline at end of file