/interpreter/tags/at_build150307/src/edu/vub/at/objects/natives/grammar/AGSymbol.java

http://ambienttalk.googlecode.com/ · Java · 130 lines · 56 code · 21 blank · 53 comment · 3 complexity · 6fc33b02debdd0449dcbc9f9c7eac924 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.ATContext;
  31. import edu.vub.at.objects.ATObject;
  32. import edu.vub.at.objects.ATText;
  33. import edu.vub.at.objects.grammar.ATSymbol;
  34. import edu.vub.at.objects.natives.NATText;
  35. import java.util.HashMap;
  36. /**
  37. * @author tvcutsem
  38. *
  39. * The native implementation of a symbol AG element.
  40. * Symbols should only be created via a call to AGSymbol.alloc
  41. * This ensures that symbols remain unique within one AmbientTalk VM.
  42. */
  43. public class AGSymbol extends AGExpression implements ATSymbol {
  44. /** hashmap shared by ALL actors/VMs, hence, thread access should be explicitly synchronized */
  45. private static final HashMap _STRINGPOOL_ = new HashMap();
  46. private final String txt_;
  47. protected AGSymbol(String txt) {
  48. txt_ = txt;
  49. }
  50. public static final AGSymbol jAlloc(String name) {
  51. synchronized (_STRINGPOOL_) {
  52. AGSymbol existing = (AGSymbol) _STRINGPOOL_.get(name);
  53. if (existing == null) {
  54. existing = new AGSymbol(name);
  55. _STRINGPOOL_.put(name, existing);
  56. }
  57. return existing;
  58. }
  59. }
  60. public static final AGSymbol alloc(NATText txt) {
  61. return jAlloc(txt.javaValue);
  62. }
  63. public ATText base_getText() { return NATText.atValue(txt_); }
  64. /**
  65. * To evaluate a symbol reference, look up the symbol in the lexical scope.
  66. *
  67. * AGSYM(txt).eval(ctx) = ctx.scope.lookup(AGSYM(txt))
  68. *
  69. * @return the value bound to this symbol in the lexical environment
  70. */
  71. public ATObject meta_eval(ATContext ctx) throws InterpreterException {
  72. return ctx.base_getLexicalScope().meta_lookup(this);
  73. }
  74. /**
  75. * Quoting a symbol results in the same symbol.
  76. *
  77. * sym.quote(ctx) = sym
  78. */
  79. public ATObject meta_quote(ATContext ctx) throws InterpreterException {
  80. return this;
  81. }
  82. public NATText meta_print() throws InterpreterException {
  83. return NATText.atValue(txt_);
  84. }
  85. public boolean isSymbol() {
  86. return true;
  87. }
  88. public ATSymbol asSymbol() {
  89. return this;
  90. }
  91. // comparison and identity operations
  92. public boolean equals(Object other) {
  93. // pointer equality is valid for symbols as they are pooled
  94. return this == other;
  95. }
  96. // important as AGSymbols are often used as keys in hash tables
  97. public int hashCode() {
  98. return this.txt_.hashCode();
  99. }
  100. public String toString() {
  101. return txt_;
  102. }
  103. /**
  104. * After deserialization, ensure that the symbol remains unique.
  105. */
  106. public ATObject meta_resolve() throws InterpreterException {
  107. return jAlloc(txt_);
  108. }
  109. }