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- <a name="Deconstruction-Functions"></a>
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- <a name="Deconstruction-Functions-1"></a>
- <h3 class="subsection">3.1.6 Deconstruction Functions</h3>
- <p>A fast native implementation of the deconstruction operation is provided
- <a name="index-deconstruction-3"></a>
- by the functions declared in ‘<tt>decons.h</tt>’.
- </p>
- <dl>
- <dt><a name="index-avm_005finitialize_005fdecons"></a><u>Function:</u> void <b>avm_initialize_decons</b><i> ()</i></dt>
- <dd><p>This should be called prior to the first call to
- <code>avm_deconstruction</code>, so as to initialize some necessary internal
- data structures. Results will be undefined if it is not.
- </p></dd></dl>
- <dl>
- <dt><a name="index-avm_005fcount_005fdecons"></a><u>Function:</u> void <b>avm_count_decons</b><i> ()</i></dt>
- <dd><p>For ecologically sound memory management, this function should be called
- at the end of a run to verify that there have been no leaks due to the
- deconstruction functions, which there won’t be unless the code in
- ‘<tt>decons.c</tt>’ has been ineptly modified. An error message to the
- effect of unreclaimed “points” could be the result otherwise.
- </p></dd></dl>
- <dl>
- <dt><a name="index-avm_005fdeconstruction"></a><u>Function:</u> list <b>avm_deconstruction</b><i> (list <var>pointer</var>, list <var>operand</var>, int *<var>fault</var>)</i></dt>
- <dd><p>Deconstructions are performed by this function, as described in
- <a href="Field.html#Field">Field</a>. In the <code>silly</code> program notation (<a href="A-Simple-Lisp-Like-Language.html#A-Simple-Lisp-Like-Language">A Simple Lisp Like Language</a>), this function computes the value
- of ([[<code>field</code>]] <code><var>pointer</var></code>) <code><var>operand</var></code>.
- </p>
- <p>For example, using the fixed list <code>avm_join(NULL,NULL)</code> as the
- <code><var>pointer</var></code> parameter will cause a copy of the operand itself
- to be returned as the result. A <code><var>pointer</var></code> equal to
- <code>avm_join(NULL,avm_join(NULL,NULL))</code> will cause a copy of
- <code>operand->tail</code> to be returned, and so on. A <code>NULL</code>
- <code><var>pointer</var></code> causes an internal error.
- </p>
- <p>If the deconstruction is invalid, as in the case of the tail of an empty
- list, the invalid deconstruction error message is returned as the
- result, and the <code>*<var>fault</var></code> parameter is set to a non-zero value.
- The <code>*<var>fault</var></code> parameter is also set to a non-zero value in the event
- of a memory overflow, and the memory overflow message is returned.
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