/interpreter/tags/at2dist041108/src/edu/vub/at/objects/natives/grammar/AGSymbol.java

http://ambienttalk.googlecode.com/ · Java · 170 lines · 77 code · 26 blank · 67 comment · 4 complexity · 3de4f3bd600e92dd8b24ddab56014b8b MD5 · raw file

  1. /**
  2. * AmbientTalk/2 Project
  3. * AGSymbol.java created on 26-jul-2006 at 16:21:55
  4. * (c) Programming Technology Lab, 2006 - 2007
  5. * Authors: Tom Van Cutsem & Stijn Mostinckx
  6. *
  7. * Permission is hereby granted, free of charge, to any person
  8. * obtaining a copy of this software and associated documentation
  9. * files (the "Software"), to deal in the Software without
  10. * restriction, including without limitation the rights to use,
  11. * copy, modify, merge, publish, distribute, sublicense, and/or
  12. * sell copies of the Software, and to permit persons to whom the
  13. * Software is furnished to do so, subject to the following
  14. * conditions:
  15. *
  16. * The above copyright notice and this permission notice shall be
  17. * included in all copies or substantial portions of the Software.
  18. *
  19. * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND,
  20. * EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES
  21. * OF MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND
  22. * NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT
  23. * HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY,
  24. * WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING
  25. * FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR
  26. * OTHER DEALINGS IN THE SOFTWARE.
  27. */
  28. package edu.vub.at.objects.natives.grammar;
  29. import edu.vub.at.exceptions.InterpreterException;
  30. import edu.vub.at.objects.ATBoolean;
  31. import edu.vub.at.objects.ATContext;
  32. import edu.vub.at.objects.ATObject;
  33. import edu.vub.at.objects.ATText;
  34. import edu.vub.at.objects.grammar.ATSymbol;
  35. import edu.vub.at.objects.natives.NATBoolean;
  36. import edu.vub.at.objects.natives.NATText;
  37. import java.util.HashMap;
  38. import java.util.HashSet;
  39. import java.util.Set;
  40. /**
  41. * @author tvcutsem
  42. *
  43. * The native implementation of a symbol AG element.
  44. * Symbols should only be created via a call to AGSymbol.alloc
  45. * This ensures that symbols remain unique within one AmbientTalk VM.
  46. */
  47. public class AGSymbol extends AGExpression implements ATSymbol {
  48. /** hashmap shared by ALL actors/VMs, hence, thread access should be explicitly synchronized */
  49. protected static final HashMap _STRINGPOOL_ = new HashMap();
  50. private final String txt_;
  51. protected AGSymbol(String txt) {
  52. txt_ = txt;
  53. }
  54. /**
  55. * Allocate and return a unique symbol object denoting the given
  56. * text string.
  57. */
  58. public static AGSymbol jAlloc(String name) {
  59. synchronized (_STRINGPOOL_) {
  60. AGSymbol existing = (AGSymbol) _STRINGPOOL_.get(name);
  61. if (existing == null) {
  62. existing = new AGSymbol(name);
  63. _STRINGPOOL_.put(name, existing);
  64. }
  65. return existing;
  66. }
  67. }
  68. /**
  69. * Allocate and return a unique symbol denoting the given native text.
  70. */
  71. public static final AGSymbol alloc(NATText txt) {
  72. return jAlloc(txt.javaValue);
  73. }
  74. public ATText base_text() { return NATText.atValue(txt_); }
  75. /**
  76. * To evaluate a symbol reference, look up the symbol in the lexical scope.
  77. *
  78. * AGSYM(txt).eval(ctx) = ctx.scope.lookup(AGSYM(txt))
  79. *
  80. * @return the value bound to this symbol in the lexical environment
  81. */
  82. public ATObject meta_eval(ATContext ctx) throws InterpreterException {
  83. return ctx.base_lexicalScope().impl_callField(this);
  84. }
  85. /**
  86. * Quoting a symbol results in the same symbol.
  87. *
  88. * sym.quote(ctx) = sym
  89. */
  90. public ATObject meta_quote(ATContext ctx) throws InterpreterException {
  91. return this;
  92. }
  93. public NATText meta_print() throws InterpreterException {
  94. return NATText.atValue(txt_);
  95. }
  96. public boolean isSymbol() {
  97. return true;
  98. }
  99. public ATSymbol asSymbol() {
  100. return this;
  101. }
  102. public boolean isAssignmentSymbol() {
  103. return false;
  104. }
  105. public AGAssignmentSymbol asAssignmentSymbol() {
  106. return (AGAssignmentSymbol) AGAssignmentSymbol.jAlloc(txt_+":=");
  107. }
  108. // comparison and identity operations
  109. public boolean equals(Object other) {
  110. // pointer equality is valid for symbols as they are pooled
  111. return this == other;
  112. }
  113. public ATBoolean base__opeql__opeql_(ATObject comparand) throws InterpreterException {
  114. return NATBoolean.atValue(this == comparand);
  115. }
  116. // important as AGSymbols are often used as keys in hash tables
  117. public int hashCode() {
  118. return this.txt_.hashCode();
  119. }
  120. public String toString() {
  121. return txt_;
  122. }
  123. /**
  124. * After deserialization, ensure that the symbol remains unique.
  125. */
  126. public ATObject meta_resolve() throws InterpreterException {
  127. return jAlloc(txt_);
  128. }
  129. /**
  130. * FV(nam) = { nam }
  131. */
  132. public Set impl_freeVariables() throws InterpreterException {
  133. HashSet singleton = new HashSet();
  134. singleton.add(this);
  135. return singleton;
  136. }
  137. /**
  138. * Within a quoted expression, a variable reference is not considered
  139. * a free variable, e.g. `(x)
  140. */
  141. public Set impl_quotedFreeVariables() throws InterpreterException {
  142. return new HashSet();
  143. }
  144. }