diff -r 000000000000 -r 1918ee327afb src/xmlpatterns/functions/qtracefn.cpp
--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/src/xmlpatterns/functions/qtracefn.cpp	Mon Jan 11 14:00:40 2010 +0000
@@ -0,0 +1,140 @@
+/****************************************************************************
+**
+** Copyright (C) 2009 Nokia Corporation and/or its subsidiary(-ies).
+** All rights reserved.
+** Contact: Nokia Corporation (qt-info@nokia.com)
+**
+** This file is part of the QtXmlPatterns module of the Qt Toolkit.
+**
+** $QT_BEGIN_LICENSE:LGPL$
+** No Commercial Usage
+** This file contains pre-release code and may not be distributed.
+** You may use this file in accordance with the terms and conditions
+** contained in the Technology Preview License Agreement accompanying
+** this package.
+**
+** GNU Lesser General Public License Usage
+** Alternatively, this file may be used under the terms of the GNU Lesser
+** General Public License version 2.1 as published by the Free Software
+** Foundation and appearing in the file LICENSE.LGPL included in the
+** packaging of this file.  Please review the following information to
+** ensure the GNU Lesser General Public License version 2.1 requirements
+** will be met: http://www.gnu.org/licenses/old-licenses/lgpl-2.1.html.
+**
+** In addition, as a special exception, Nokia gives you certain additional
+** rights.  These rights are described in the Nokia Qt LGPL Exception
+** version 1.1, included in the file LGPL_EXCEPTION.txt in this package.
+**
+** If you have questions regarding the use of this file, please contact
+** Nokia at qt-info@nokia.com.
+**
+**
+**
+**
+**
+**
+**
+**
+** $QT_END_LICENSE$
+**
+****************************************************************************/
+
+#include "qcommonsequencetypes_p.h"
+#include "qcommonvalues_p.h"
+#include "qitemmappingiterator_p.h"
+#include "qpatternistlocale_p.h"
+
+#include "qtracefn_p.h"
+
+QT_BEGIN_NAMESPACE
+
+using namespace QPatternist;
+
+namespace QPatternist
+{
+    /**
+     * @short TraceCallback is a MappingCallback and takes care of
+     * the tracing of each individual item.
+     *
+     * Because Patternist must be thread safe, TraceFN creates a TraceCallback
+     * each time the function is evaluated. In other words, TraceFN, which is
+     * an Expression sub class, can't modify its members, but MappingCallback
+     * does not have this limitation since it's created on a per evaluation basis.
+     *
+     * @author Frans Englich <frans.englich@nokia.com>
+     */
+    class TraceCallback : public QSharedData
+    {
+    public:
+        typedef QExplicitlySharedDataPointer<TraceCallback> Ptr;
+
+        inline TraceCallback(const QString &msg) : m_position(0),
+                                                   m_msg(msg)
+        {
+        }
+
+        /**
+         * Performs the actual tracing.
+         */
+        Item mapToItem(const Item &item,
+                            const DynamicContext::Ptr &context)
+        {
+            QTextStream out(stderr);
+            ++m_position;
+            if(m_position == 1)
+            {
+                if(item)
+                {
+                    out << qPrintable(m_msg)
+                        << " : "
+                        << qPrintable(item.stringValue());
+                }
+                else
+                {
+                    out << qPrintable(m_msg)
+                        << " : ("
+                        << qPrintable(formatType(context->namePool(), CommonSequenceTypes::Empty))
+                        << ")\n";
+                    return Item();
+                }
+            }
+            else
+            {
+                out << qPrintable(item.stringValue())
+                    << '['
+                    << m_position
+                    << "]\n";
+            }
+
+            return item;
+        }
+
+    private:
+        xsInteger m_position;
+        const QString m_msg;
+    };
+}
+
+Item::Iterator::Ptr TraceFN::evaluateSequence(const DynamicContext::Ptr &context) const
+{
+    const QString msg(m_operands.last()->evaluateSingleton(context).stringValue());
+
+    return makeItemMappingIterator<Item>(TraceCallback::Ptr(new TraceCallback(msg)),
+                                              m_operands.first()->evaluateSequence(context),
+                                              context);
+}
+
+Item TraceFN::evaluateSingleton(const DynamicContext::Ptr &context) const
+{
+    const QString msg(m_operands.last()->evaluateSingleton(context).stringValue());
+    const Item item(m_operands.first()->evaluateSingleton(context));
+
+    return TraceCallback::Ptr(new TraceCallback(msg))->mapToItem(item, context);
+}
+
+SequenceType::Ptr TraceFN::staticType() const
+{
+    return m_operands.first()->staticType();
+}
+
+QT_END_NAMESPACE