diff --git a/Implab/Diagnostics/Extensions.cs b/Implab/Diagnostics/Extensions.cs
--- a/Implab/Diagnostics/Extensions.cs
+++ b/Implab/Diagnostics/Extensions.cs
@@ -10,6 +10,17 @@
                 TraceContext.Instance.Leave();
             });
         }
+
+        public static IPromise EndLogicalOperation(this IPromise promise) {
+            Safe.ArgumentNotNull(promise, "promise");
+            var op = TraceContext.Instance.DetachLogicalOperation();
+
+            return promise.Anyway(() => {
+                TraceContext.Instance.EnterLogicalOperation(op,true);
+                TraceLog.EndLogicalOperation();
+                TraceContext.Instance.Leave();
+            });
+        }
     }
 }
 
diff --git a/Implab/Diagnostics/TraceContext.cs b/Implab/Diagnostics/TraceContext.cs
--- a/Implab/Diagnostics/TraceContext.cs
+++ b/Implab/Diagnostics/TraceContext.cs
@@ -41,9 +41,10 @@ namespace Implab.Diagnostics {
         }
 
         public void EnterLogicalOperation(LogicalOperation operation, bool takeOwnership) {
-            LogChannel<TraceEvent>.Default.LogEvent(new TraceEvent(TraceEventType.Attach, String.Format("{0} -> [{1}]", operation.Name, m_threadId)));
+            var prev = CurrentOperation;
             m_stack.Push(m_current);
             m_current = new OperationContext(operation, takeOwnership);
+            LogChannel<TraceEvent>.Default.LogEvent(new TraceEvent(takeOwnership ? TraceEventType.Attach : TraceEventType.Enter, String.Format("{0} -> {1}",prev.Name, operation.Name)));
         }
 
         public void StartLogicalOperation(string name) {
@@ -61,15 +62,17 @@ namespace Implab.Diagnostics {
         }
 
         public LogicalOperation DetachLogicalOperation() {
-            var op = m_current.DetachLogicalOperation();
-            LogChannel<TraceEvent>.Default.LogEvent(new TraceEvent(TraceEventType.Detach, String.Format("[{0}] -> {1}", m_threadId, op.Name)));
-            return op;
+            var prev = m_current.DetachLogicalOperation();
+            LogChannel<TraceEvent>.Default.LogEvent(new TraceEvent(TraceEventType.Detach, String.Format("{0} -> {1}",prev.Name, CurrentOperation.Name)));
+            return prev;
         }
 
         public void Leave() {
             if (m_stack.Count > 0) {
                 m_current.Leave();
+                var prev = CurrentOperation;
                 m_current = m_stack.Pop();
+                LogChannel<TraceEvent>.Default.LogEvent(new TraceEvent(TraceEventType.Leave, String.Format("{0} -> {1}", prev.Name, CurrentOperation.Name)));
             } else {
                 TraceLog.TraceWarning("Attemtp to leave the last operation context");
                 m_current = OperationContext.EMPTY;
diff --git a/Implab/Diagnostics/TraceEventType.cs b/Implab/Diagnostics/TraceEventType.cs
--- a/Implab/Diagnostics/TraceEventType.cs
+++ b/Implab/Diagnostics/TraceEventType.cs
@@ -13,5 +13,7 @@ namespace Implab.Diagnostics {
         OperationCompleted,
         Attach,
         Detach,
+        Enter,
+        Leave
     }
 }
diff --git a/Implab/IPromiseT.cs b/Implab/IPromiseT.cs
--- a/Implab/IPromiseT.cs
+++ b/Implab/IPromiseT.cs
@@ -1,7 +1,4 @@
 using System;
-using System.Collections.Generic;
-using System.Linq;
-using System.Text;
 
 namespace Implab {
     public interface IPromise<T> : IPromise {
diff --git a/Implab/Safe.cs b/Implab/Safe.cs
--- a/Implab/Safe.cs
+++ b/Implab/Safe.cs
@@ -44,7 +44,7 @@ namespace Implab
         }
 
         [DebuggerStepThrough]
-        public static IPromise<T> GuargPromise<T>(Func<T> action) {
+        public static IPromise<T> InvokePromise<T>(Func<T> action) {
             ArgumentNotNull(action, "action");
 
             var p = new Promise<T>();
@@ -58,11 +58,11 @@ namespace Implab
         }
 
         [DebuggerStepThrough]
-        public static IPromise<T> GuardPromise<T>(Func<IPromise<T>> action) {
+        public static IPromise<T> InvokePromise<T>(Func<IPromise<T>> action) {
             ArgumentNotNull(action, "action");
 
             try {
-                return action();
+                return action() ?? Promise<T>.ExceptionToPromise(new Exception("The action returned null"));
             } catch (Exception err) {
                 return Promise<T>.ExceptionToPromise(err);
             }
diff --git a/MonoPlay/Program.cs b/MonoPlay/Program.cs
--- a/MonoPlay/Program.cs
+++ b/MonoPlay/Program.cs
@@ -6,6 +6,9 @@ using Implab;
 namespace MonoPlay {
     class MainClass {
         public static void Main(string[] args) {
+            if (args == null)
+                throw new ArgumentNullException("args");
+
             var listener = new ConsoleTraceListener(true);
             listener.Subscribe<TraceEvent>();
 
@@ -13,12 +16,10 @@ namespace MonoPlay {
 
             TraceLog.StartLogicalOperation("program");
 
-            Console.WriteLine("Hello World!");
-
             TraceLog.StartLogicalOperation("async");
             AsyncPool.Invoke(() => {
                 TraceLog.TraceInformation("Hello async");
-                TraceLog.StartLogicalOperation();
+                TraceLog.StartLogicalOperation("foo");
                 return 0;
             })
                 .EndLogicalOperation()