Exception-Handling.html 6.9 KB

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  57. <a name="Exception-Handling-1"></a>
  58. <h3 class="subsection">2.7.15 Exception Handling</h3>
  59. <a name="index-exceptions-2"></a>
  60. <p>In quite a few cases, the properties given for the operator up to this
  61. point do not imply any particular result. A good example would be an
  62. expression such as [[<code>left</code>]] <code>nil</code>, which appears to
  63. represent the left side of an empty pair. It can be argued that
  64. expressions like this have no sensible interpretation and should never
  65. be used, so it would be appropriate to leave them undefined. On the
  66. other hand, attempts to evaluate such expressions occur frequently by
  67. mistake, and in any case, the virtual machine emulator should be
  68. designed to do something reasonable about them if only for the sake of
  69. reporting the error. The chosen remedy for this situation addresses the
  70. need for error reporting, and also turns out to be useful in other ways.
  71. </p>
  72. <table class="menu" border="0" cellspacing="0">
  73. <tr><td align="left" valign="top"><a href="A-Hierarchy-of-Sets.html#A-Hierarchy-of-Sets">2.7.15.1 A Hierarchy of Sets</a></td><td>&nbsp;&nbsp;</td><td align="left" valign="top">
  74. </td></tr>
  75. <tr><td align="left" valign="top"><a href="Operator-Generalization.html#Operator-Generalization">2.7.15.2 Operator Generalization</a></td><td>&nbsp;&nbsp;</td><td align="left" valign="top">
  76. </td></tr>
  77. <tr><td align="left" valign="top"><a href="Error-Messages.html#Error-Messages">2.7.15.3 Error Messages</a></td><td>&nbsp;&nbsp;</td><td align="left" valign="top">
  78. </td></tr>
  79. <tr><td align="left" valign="top"><a href="Expedient-Error-Messages.html#Expedient-Error-Messages">2.7.15.4 Expedient Error Messages</a></td><td>&nbsp;&nbsp;</td><td align="left" valign="top">
  80. </td></tr>
  81. <tr><td align="left" valign="top"><a href="Computable-Error-Messages.html#Computable-Error-Messages">2.7.15.5 Computable Error Messages</a></td><td>&nbsp;&nbsp;</td><td align="left" valign="top">
  82. </td></tr>
  83. <tr><td align="left" valign="top"><a href="Exception-Handler-Usage.html#Exception-Handler-Usage">2.7.15.6 Exception Handler Usage</a></td><td>&nbsp;&nbsp;</td><td align="left" valign="top">
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