Github user ottobackwards commented on a diff in the pull request:
https://github.com/apache/metron/pull/884#discussion_r159922114
--- Diff:
metron-stellar/stellar-common/src/main/java/org/apache/metron/stellar/common/shell/StellarShellExecutor.java
---
@@ -0,0 +1,79 @@
+/*
+ *
+ * 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.dsl.Context;
+import org.apache.metron.stellar.dsl.functions.resolver.FunctionResolver;
+
+import java.util.Map;
+import java.util.Optional;
+
+/**
+ * Responsible for executing Stellar in a shell-like environment.
+ *
+ * Provides the additional capabilities expected of executing Stellar
+ * in a shell-like environment including maintaining state, variable
assignment,
+ * magic commands, doc strings, and comments.
+ */
+public interface StellarShellExecutor extends StellarExecutionNotifier {
+
+ /**
+ * Initialize the Stellar executor.
+ */
+ void init();
+
+ /**
+ * Execute the Stellar expression.
+ * @param expression The Stellar expression to execute.
+ * @return The result of executing the Stellar expression.
+ */
+ StellarResult execute(String expression);
+
+ /**
+ * Update the state of the executor by assign a value to a variable.
+ * @param variable The name of the variable.
+ * @param value The value to assign.
+ * @param expression The expression that resulted in the given value.
Optional.
+ */
+ void assign(String variable, Object value, Optional<String> expression);
+
+ /**
+ * The current state of the Stellar execution environment.
+ */
--- End diff --
Are variables the only state we can have? I'm going to have to change this
when I write the debugger.
---
