Github user cloud-fan commented on a diff in the pull request:
https://github.com/apache/spark/pull/21954#discussion_r208267632
--- Diff:
sql/catalyst/src/main/scala/org/apache/spark/sql/catalyst/expressions/higherOrderFunctions.scala
---
@@ -0,0 +1,212 @@
+/*
+ * 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.spark.sql.catalyst.expressions
+
+import java.util.concurrent.atomic.AtomicReference
+
+import org.apache.spark.sql.catalyst.InternalRow
+import org.apache.spark.sql.catalyst.expressions.codegen._
+import org.apache.spark.sql.catalyst.expressions.codegen.Block._
+import org.apache.spark.sql.catalyst.util.{ArrayData, GenericArrayData}
+import org.apache.spark.sql.types._
+
+/**
+ * A named lambda variable.
+ */
+case class NamedLambdaVariable(
+ name: String,
+ dataType: DataType,
+ nullable: Boolean,
+ value: AtomicReference[Any] = new AtomicReference(),
+ exprId: ExprId = NamedExpression.newExprId)
+ extends LeafExpression
+ with NamedExpression
+ with CodegenFallback {
+
+ override def qualifier: Option[String] = None
+
+ override def newInstance(): NamedExpression =
+ copy(value = new AtomicReference(), exprId = NamedExpression.newExprId)
+
+ override def toAttribute: Attribute = {
+ AttributeReference(name, dataType, nullable, Metadata.empty)(exprId,
None)
+ }
+
+ override def eval(input: InternalRow): Any = value.get
+
+ override def toString: String = s"lambda $name#${exprId.id}$typeSuffix"
+
+ override def simpleString: String = s"lambda $name#${exprId.id}:
${dataType.simpleString}"
+}
+
+/**
+ * A lambda function and its arguments. A lambda function can be hidden
when a user wants to
+ * process an completely independent expression in a
[[HigherOrderFunction]], the lambda function
+ * and its variables are then only used for internal bookkeeping within
the higher order function.
+ */
+case class LambdaFunction(
+ function: Expression,
+ arguments: Seq[NamedExpression],
+ hidden: Boolean = false)
+ extends Expression with CodegenFallback {
+
+ override def children: Seq[Expression] = function +: arguments
+ override def dataType: DataType = function.dataType
+ override def nullable: Boolean = function.nullable
+
+ lazy val bound: Boolean = arguments.forall(_.resolved)
+
+ override def eval(input: InternalRow): Any = function.eval(input)
+}
+
+/**
+ * A higher order function takes one or more (lambda) functions and
applies these to some objects.
+ * The function produces a number of variables which can be consumed by
some lambda function.
+ */
+trait HigherOrderFunction extends Expression {
+
+ override def children: Seq[Expression] = inputs ++ functions
+
+ /**
+ * Inputs to the higher ordered function.
+ */
+ def inputs: Seq[Expression]
+
+ /**
+ * All inputs have been resolved. This means that the types and
nullabilty of (most of) the
+ * lambda function arguments is known, and that we can start binding the
lambda functions.
+ */
+ lazy val inputResolved: Boolean = inputs.forall(_.resolved)
+
+ /**
+ * Functions applied by the higher order function.
+ */
+ def functions: Seq[Expression]
--- End diff --
seems function must be `LambdaFunction`, why don't we enforce it at type
level?
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