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.sql;
  
  import org.apache.calcite.rel.type.RelDataType;
  import org.apache.calcite.sql.parser.SqlParserPos;
  import org.apache.calcite.sql.validate.SqlLambdaScope;
  import org.apache.calcite.sql.validate.SqlValidator;
  import org.apache.calcite.sql.validate.SqlValidatorScope;
  import org.apache.calcite.util.UnmodifiableArrayList;
  
  import org.checkerframework.checker.nullness.qual.Nullable;
  
  import java.util.List;
  
  import static com.google.common.collect.ImmutableList.toImmutableList;
  
  import static org.apache.calcite.sql.SqlPivot.stripList;
  
  import static java.util.Objects.requireNonNull;
  
  /**
   * A <code>SqlLambda</code> is a node of a parse tree which
   * represents a lambda expression.
   */
  public class SqlLambda extends SqlCall {
  
    public static final SqlOperator OPERATOR = new SqlLambdaOperator();
  
    SqlNodeList parameters;
    SqlNode expression;
  
    public SqlLambda(SqlParserPos pos, SqlNodeList parameters,
        SqlNode expression) {
      super(pos);
      this.parameters = parameters;
      this.expression = expression;
    }
  
    //~ Methods ----------------------------------------------------------------
  
    @Override public SqlKind getKind() {
      return SqlKind.LAMBDA;
    }
  
    @Override public SqlOperator getOperator() {
      return OPERATOR;
    }
  
    @Override public List<SqlNode> getOperandList() {
      return UnmodifiableArrayList.of(parameters, expression);
    }
  
    @Override public void setOperand(int i, @Nullable SqlNode operand) {
      switch (i) {
      case 0:
        parameters = requireNonNull((SqlNodeList) operand, "parameters");
        break;
      case 1:
        expression = requireNonNull(operand, "operand");
        break;
      default:
        throw new AssertionError(i);
      }
    }
  
    @Override public void unparse(SqlWriter writer, int leftPrec, int rightPrec) {
      if (parameters.size() != 1) {
        writer.list(SqlWriter.FrameTypeEnum.PARENTHESES, SqlWriter.COMMA, stripList(parameters));
      } else {
        parameters.unparse(writer, leftPrec, rightPrec);
      }
      writer.keyword(OPERATOR.getName());
      expression.unparse(writer, leftPrec, rightPrec);
    }
  
    public SqlNodeList getParameters() {
      return parameters;
    }
  
    public SqlNode getExpression() {
      return expression;
    }
  
    /**
     * The {@code SqlLambdaOperator} represents a lambda expression.
     * The syntax :
     * {@code IDENTIFIER -> EXPRESSION} or {@code (IDENTIFIER, IDENTIFIER, ...) -> EXPRESSION}.
     */
    private static class SqlLambdaOperator extends SqlSpecialOperator {
  
      SqlLambdaOperator() {
        super("->", SqlKind.LAMBDA);
      }
  
      @Override public RelDataType deriveType(
          SqlValidator validator, SqlValidatorScope scope, SqlCall call) {
        final SqlLambda lambdaExpr = (SqlLambda) call;
        final SqlLambdaScope lambdaScope = (SqlLambdaScope) scope;
        final List<String> paramNames = lambdaExpr.getParameters().stream()
            .map(SqlNode::toString)
            .collect(toImmutableList());
        final List<RelDataType> paramTypes = lambdaScope.getParameterTypes().values()
            .stream()
            .collect(toImmutableList());
        final RelDataType paramRowType =
            validator.getTypeFactory().createStructType(paramTypes, paramNames);
        final RelDataType returnType = validator.getValidatedNodeType(lambdaExpr.getExpression());
        return validator.getTypeFactory().createFunctionSqlType(paramRowType, returnType);
      }
    }
  }
  