/interpreter/tags/at2dist130208/src/edu/vub/at/objects/natives/grammar/AGBegin.java

http://ambienttalk.googlecode.com/ · Java · 97 lines · 38 code · 10 blank · 49 comment · 3 complexity · 9f25f400414855dbb1f0fee8d849156d MD5 · raw file

  1. /**
  2. * AmbientTalk/2 Project
  3. * AGBegin.java created on 26-jul-2006 at 12:26:48
  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.eval.Evaluator;
  30. import edu.vub.at.exceptions.InterpreterException;
  31. import edu.vub.at.exceptions.XTypeMismatch;
  32. import edu.vub.at.objects.ATContext;
  33. import edu.vub.at.objects.ATObject;
  34. import edu.vub.at.objects.ATTable;
  35. import edu.vub.at.objects.grammar.ATBegin;
  36. import edu.vub.at.objects.natives.NATNumber;
  37. import edu.vub.at.objects.natives.NATText;
  38. import edu.vub.at.objects.natives.OBJNil;
  39. /**
  40. * AGBegin represents the abstract grammar element of a list of statements.
  41. * Examples:
  42. * <tt>a ; b ; c</tt>
  43. *
  44. * @author tvcutsem
  45. */
  46. public final class AGBegin extends NATAbstractGrammar implements ATBegin {
  47. private final ATTable statements_;
  48. public AGBegin(ATTable statements) {
  49. statements_ = statements;
  50. }
  51. /**
  52. * AGBEGIN encapsulates a sequence of statements and evaluates each of these statements in turn.
  53. * The return value is the value of the last statement.
  54. *
  55. * AGBEGIN([statement | statements]).eval(ctx) = statement.eval(ctx) ; BEGIN(statements).eval(ctx)
  56. * AGBEGIN([statement]).eval(ctx) = statement.eval(ctx)
  57. *
  58. * Note that this implementation of begin is *not* tail-recursive.
  59. * Tail-recursion is made impossible because Java will not allow a return
  60. * to the caller until the last expression is also evaluated. Tail-recursion optimalisation
  61. * requires a minimal form of explicit continuations.
  62. */
  63. public ATObject meta_eval(ATContext ctx) throws InterpreterException {
  64. NATNumber siz = statements_.base_length().asNativeNumber();
  65. int lastIdx = siz.javaValue;
  66. if (lastIdx == 0) {
  67. return OBJNil._INSTANCE_;
  68. }
  69. for (int i = 1; i < lastIdx; i++) {
  70. statements_.base_at(NATNumber.atValue(i)).meta_eval(ctx);
  71. }
  72. return statements_.base_at(NATNumber.atValue(lastIdx)).meta_eval(ctx);
  73. }
  74. /**
  75. * AGBEGIN(statements*).quote(ctx) = AGBEGIN((statements*).quote(ctx))
  76. */
  77. public ATObject meta_quote(ATContext ctx) throws InterpreterException {
  78. return new AGBegin(statements_.meta_quote(ctx).asTable());
  79. }
  80. public ATTable base_statements() { return statements_; }
  81. public NATText meta_print() throws InterpreterException {
  82. return Evaluator.printAsStatements(statements_);
  83. }
  84. public ATBegin asBegin() throws XTypeMismatch {
  85. return this;
  86. }
  87. }