Github user nickwallen commented on a diff in the pull request:
https://github.com/apache/metron/pull/884#discussion_r159497124
--- Diff:
metron-stellar/stellar-common/src/main/java/org/apache/metron/stellar/common/shell/StellarExecutionListeners.java
---
@@ -0,0 +1,51 @@
+/*
+ *
+ * Licensed to the Apache Software Foundation (ASF) under one
+ * or more contributor license agreements. See the NOTICE file
+ * distributed with this work for additional information
+ * regarding copyright ownership. The ASF licenses this file
+ * to you under the Apache License, Version 2.0 (the
+ * "License"); you may not use this file except in compliance
+ * with the License. You may obtain a copy of the License at
+ *
+ * http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or
implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ *
+ */
+package org.apache.metron.stellar.common.shell;
+
+import org.apache.metron.stellar.common.shell.specials.SpecialCommand;
+import org.apache.metron.stellar.dsl.StellarFunctionInfo;
+
+/**
+ * A listener will be notified about events that occur during the
+ * execution of Stellar expressions.
+ */
+public class StellarExecutionListeners {
+
+ /**
+ * A listener that is notified when a function is defined.
+ */
+ public interface FunctionDefinedListener {
+ void whenFunctionDefined(StellarFunctionInfo functionInfo);
+ }
--- End diff --
I used an event listener pattern so that external entities could get
notified when things occur during the execution of Stellar. For example, the
auto-completer needs to know when a variable is defined.
---
