1 /*
2 * Licensed to the Apache Software Foundation (ASF) under one or more
3 * contributor license agreements. See the NOTICE file distributed with
4 * this work for additional information regarding copyright ownership.
5 * The ASF licenses this file to You under the Apache License, Version 2.0
6 * (the "License"); you may not use this file except in compliance with
7 * the License. You may obtain a copy of the License at
8 *
9 * http://www.apache.org/licenses/LICENSE-2.0
10 *
11 * Unless required by applicable law or agreed to in writing, software
12 * distributed under the License is distributed on an "AS IS" BASIS,
13 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
14 * See the License for the specific language governing permissions and
15 * limitations under the License.
16 */
17 package org.apache.commons.jexl3.internal;
18
19 import java.util.ArrayDeque;
20 import java.util.Deque;
21
22 /**
23 * The set of valued symbols defined in a lexical frame.
24 * <p>The symbol identifiers are determined by the functional scope. Since the frame contains values of
25 * all symbols in the functional scope, the lexical frame preserves values of symbols reused for local
26 * definition.
27 */
28 public class LexicalFrame extends LexicalScope {
29 /**
30 * The script frame.
31 */
32 private final Frame frame;
33 /**
34 * Previous frame.
35 */
36 protected final LexicalFrame previous;
37 /**
38 * The stack of values in the lexical frame.
39 * <p>[symbol identifier, value] are stacked in pairs</p>
40 */
41 private Deque<Object> stack;
42
43 /**
44 * Lexical frame ctor.
45 *
46 * @param scriptf the script frame
47 * @param outerf the previous lexical frame
48 */
49 public LexicalFrame(final Frame scriptf, final LexicalFrame outerf) {
50 this.previous = outerf;
51 this.frame = scriptf;
52 }
53
54 /**
55 * Copy ctor.
56 *
57 * @param src the frame to copy
58 */
59 public LexicalFrame(final LexicalFrame src) {
60 super(src);
61 frame = src.frame;
62 previous = src.previous;
63 stack = src.stack != null ? new ArrayDeque<>(src.stack) : null;
64 }
65
66 /**
67 * Define the arguments.
68 *
69 * @return this frame
70 */
71 public LexicalFrame defineArgs() {
72 if (frame != null) {
73 final int argc = frame.getScope().getArgCount();
74 for (int a = 0; a < argc; ++a) {
75 super.addSymbol(a);
76 }
77 }
78 return this;
79 }
80
81 /**
82 * Defines a symbol.
83 *
84 * @param symbol the symbol to define
85 * @param capture whether this redefines a captured symbol
86 * @return true if symbol is defined, false otherwise
87 */
88 public boolean defineSymbol(final int symbol, final boolean capture) {
89 final boolean declared = addSymbol(symbol);
90 if (declared && capture) {
91 if (stack == null) {
92 stack = new ArrayDeque<>();
93 }
94 stack.push(symbol);
95 Object value = frame.get(symbol);
96 if (value == null) {
97 value = this;
98 }
99 stack.push(value);
100 }
101 return declared;
102 }
103
104 /**
105 * Pops back values and lexical frame.
106 *
107 * @return the previous frame
108 */
109 public LexicalFrame pop() {
110 // undefine all symbols
111 clearSymbols(s -> frame.set(s, Scope.UNDEFINED));
112 // restore values of captured symbols that were overwritten
113 if (stack != null) {
114 while (!stack.isEmpty()) {
115 Object value = stack.pop();
116 if (value == Scope.UNDECLARED) {
117 value = Scope.UNDEFINED;
118 } else if (value == this) {
119 value = null;
120 }
121 final int symbol = (Integer) stack.pop();
122 frame.set(symbol, value);
123 }
124 }
125 return previous;
126 }
127
128 }