--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/truffle/com.oracle.truffle.api/src/com/oracle/truffle/api/instrument/WrapperNode.java	Sun Sep 20 15:51:39 2015 -0700
@@ -0,0 +1,89 @@
+/*
+ * Copyright (c) 2013, 2015, Oracle and/or its affiliates. All rights reserved.
+ * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
+ *
+ * This code is free software; you can redistribute it and/or modify it
+ * under the terms of the GNU General Public License version 2 only, as
+ * published by the Free Software Foundation.  Oracle designates this
+ * particular file as subject to the "Classpath" exception as provided
+ * by Oracle in the LICENSE file that accompanied this code.
+ *
+ * This code is distributed in the hope that it will be useful, but WITHOUT
+ * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
+ * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
+ * version 2 for more details (a copy is included in the LICENSE file that
+ * accompanied this code).
+ *
+ * You should have received a copy of the GNU General Public License version
+ * 2 along with this work; if not, write to the Free Software Foundation,
+ * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
+ *
+ * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
+ * or visit www.oracle.com if you need additional information or have any
+ * questions.
+ */
+package com.oracle.truffle.api.instrument;
+
+import com.oracle.truffle.api.TruffleLanguage;
+import com.oracle.truffle.api.nodes.Node;
+
+/**
+ * A {@link Node} instance that must be inserted into a Truffle AST in order to enable
+ * {@linkplain Instrument instrumentation} at a particular Guest Language (GL) node. Implementations
+ * must ensure that {@link TruffleLanguage#isInstrumentable(Node)} returns {@code false}.
+ * <p>
+ * The implementation must be GL-specific. A wrapper <em>decorates</em> a GL AST node (the wrapper's
+ * <em>child</em>) by acting as a transparent <em>proxy</em> with respect to the GL's execution
+ * semantics.
+ * <p>
+ * Instrumentation at the wrapped node is implemented by an instance of {@link EventHandlerNode}
+ * attached as a second child of the {@link WrapperNode}.
+ * <p>
+ * A wrapper is obliged to notify its attached {@link EventHandlerNode} when execution events occur
+ * at the wrapped AST node during program execution.
+ * <p>
+ * When a GL AST is cloned, the {@link WrapperNode}, its {@link EventHandlerNode} and any
+ * {@linkplain Instrument instrumentation} are also cloned; they are in effect part of the GL AST.
+ * An instance of {@link Probe} represents abstractly the instrumentation at a particular location
+ * in a GL AST; it tracks all the copies of the Wrapper and attached instrumentation, and acts as a
+ * single point of access for tools.
+ * <p>
+ * Implementation guidelines:
+ * <ol>
+ * <li>Each GL implementation must implement a WrapperNode implementation for each AST context in
+ * which Instrumentation is to be supported.</li>
+ * <li>The wrapper type should descend from the <em>GL-specific node class</em>.</li>
+ * <li>Must have a field: {@code @Child private <GL>Node child;}</li>
+ * <li>Must have a field: {@code @Child private EventHandlerNode eventHandlerNode;}</li>
+ * <li>The wrapper must act as a <em>proxy</em> for its child, which means implementing every
+ * possible <em>execute-</em> method that gets called on guest language AST node types by their
+ * parents, and passing along each call to its child.</li>
+ * <li>Method {@code Probe getProbe()} should be implemented as {@code eventHandlerNode.getProbe();}
+ * <li>Method {@code insertProbe(EventHandlerNode)} should be implemented as
+ * {@code this.eventHandlerNode=insert(eventHandlerNode);}</li>
+ * <li>Most importantly, Wrappers must be implemented so that Truffle optimization will reduce their
+ * runtime overhead to zero when there are no attached {@link Instrument}s.</li>
+ * </ol>
+ * <p>
+ *
+ * @see Instrument
+ */
+public interface WrapperNode extends InstrumentationNode {
+
+    /**
+     * Gets the node being "wrapped", i.e. the AST node for which
+     * {@linkplain InstrumentationNode.EventHandlerNode execution events} will be reported through
+     * the Instrumentation Framework.
+     */
+    Node getChild();
+
+    /**
+     * Gets the {@link Probe} responsible for installing this wrapper.
+     */
+    Probe getProbe();
+
+    /**
+     * Implementation support for completing a newly created wrapper node.
+     */
+    void insertEventHandlerNode(EventHandlerNode eventHandlerNode);
+}