// Copyright 2014 Google Inc. All rights reserved.
//
// Licensed 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 com.google.devtools.build.lib.syntax;
import com.google.devtools.build.lib.events.Location;
import java.io.Serializable;
import java.util.ArrayList;
import java.util.Collections;
import java.util.List;
import javax.annotation.Nullable;
/**
* Syntax node for lists comprehension expressions.
*
*
A list comprehension contains one or more clauses, e.g.
* [a+d for a in b if c for d in e]
* contains three clauses: "for a in b", "if c", "for d in e".
* For and If clauses can happen in any order, except that the first one has to be a For.
*
*
The code above can be expanded as:
*
* for a in b:
* if c:
* for d in e:
* result.append(a+d)
*
* result is initialized to [] and is the return value of the whole expression.
*/
public final class ListComprehension extends Expression {
/**
* The interface implemented by ForClause and (later) IfClause.
* A list comprehension consists of one or many Clause.
*/
public interface Clause extends Serializable {
/**
* The evaluation of the list comprehension is based on recursion. Each clause may
* call recursively evalStep (ForClause will call it multiple times, IfClause will
* call it zero or one time) which will evaluate the next clause. To know which clause
* is the next one, we pass a step argument (it represents the index in the clauses
* list). Results are aggregated in the result argument, and are populated by
* evalStep.
*
* @param env environment in which we do the evaluation.
* @param result the agreggated results of the list comprehension.
* @param step the index of the next clause to evaluate.
*/
abstract void eval(Environment env, List