content: /*
   * 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.calcite.interpreter;
  
  import org.apache.calcite.DataContext;
  import org.apache.calcite.linq4j.Enumerable;
  import org.apache.calcite.rel.RelNode;
  import org.apache.calcite.rel.type.RelDataType;
  import org.apache.calcite.rex.RexNode;
  
  import org.checkerframework.checker.nullness.qual.Nullable;
  
  import java.util.List;
  
  /**
   * Context while converting a tree of {@link RelNode} to a program
   * that can be run by an {@link Interpreter}.
   */
  public interface Compiler {
  
    /** Compiles an expression to an executable form. */
    Scalar compile(List<RexNode> nodes, @Nullable RelDataType inputRowType);
  
    RelDataType combinedRowType(List<RelNode> inputs);
  
    Source source(RelNode rel, int ordinal);
  
    /**
     * Creates a Sink for a relational expression to write into.
     *
     * <p>This method is generally called from the constructor of a {@link Node}.
     * But a constructor could instead call
     * {@link #enumerable(RelNode, Enumerable)}.
     *
     * @param rel Relational expression
     * @return Sink
     */
    Sink sink(RelNode rel);
  
    /** Tells the interpreter that a given relational expression wishes to
     * give its output as an enumerable.
     *
     * <p>This is as opposed to the norm, where a relational expression calls
     * {@link #sink(RelNode)}, then its {@link Node#run()} method writes into that
     * sink.
     *
     * @param rel Relational expression
     * @param rowEnumerable Contents of relational expression
     */
    void enumerable(RelNode rel, Enumerable<Row> rowEnumerable);
  
    DataContext getDataContext();
  
    Context createContext();
  
  }
  