--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/Implab/FuncChainTaskBase.cs	Sun Mar 08 02:52:27 2015 +0300
@@ -0,0 +1,60 @@
+using System;
+using System.Threading;
+
+namespace Implab {
+    public class FuncChainTaskBase<TResult> : AbstractPromise<TResult> {
+        readonly Func<Exception, IPromise<TResult>> m_error;
+        readonly Func<Exception, IPromise<TResult>> m_cancel;
+
+        int m_cancelationLock;
+
+        protected FuncChainTaskBase( Func<Exception, IPromise<TResult>> error, Func<Exception, IPromise<TResult>> cancel) {
+            m_error = error;
+            m_cancel = cancel;
+        }
+
+        public void Reject(Exception error) {
+            if (LockCancelation())
+                HandleErrorInternal(error);
+        }
+
+        public override void CancelOperation(Exception reason) {
+            if (m_cancel != null && LockCancelation()) {
+                try {
+                    Observe(m_cancel(reason));
+                } catch(Exception err) {
+                    HandleErrorInternal(err);
+                }
+            }
+
+        }
+
+        protected void HandleErrorInternal(Exception error) {
+            if (m_error != null) {
+                try {
+                    Observe(m_error(error));
+                } catch(Exception err) {
+                    SetError(err);
+                }
+            } else {
+                SetError(error);
+            }
+        }
+
+        protected void Observe(IPromise<TResult> operation) {
+            if (operation == null)
+                throw new NullReferenceException("The task returned null promise");
+
+            // pass operation results to the current promise
+            operation.On(SetResult, SetError, SetCancelled);
+
+            // pass the cancelation request
+            CancellationRequested(operation.Cancel);
+        }
+
+        protected bool LockCancelation() {
+            return 0 == Interlocked.CompareExchange(ref m_cancelationLock, 1, 0);
+        }
+    }
+}
+