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<title>Debugging with GDB: Iterators In Guile</title>
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<a name="Iterators-In-Guile"></a>
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<div class="header">
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<p>
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Previous: <a href="Memory-Ports-in-Guile.html#Memory-Ports-in-Guile" accesskey="p" rel="previous">Memory Ports in Guile</a>, Up: <a href="Guile-API.html#Guile-API" accesskey="u" rel="up">Guile API</a> [<a href="index.html#SEC_Contents" title="Table of contents" rel="contents">Contents</a>][<a href="Concept-Index.html#Concept-Index" title="Index" rel="index">Index</a>]</p>
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<hr>
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<a name="Iterators-In-Guile-1"></a>
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<h4 class="subsubsection">23.3.3.25 Iterators In Guile</h4>
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<a name="index-guile-iterators"></a>
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<a name="index-_003cgdb_003aiterator_003e"></a>
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<p>A simple iterator facility is provided to allow, for example,
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iterating over the set of program symbols without having to first
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construct a list of all of them. A useful contribution would be
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to add support for SRFI 41 and SRFI 45.
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</p>
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<dl>
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<dt><a name="index-make_002diterator"></a>Scheme Procedure: <strong>make-iterator</strong> <em>object progress next!</em></dt>
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<dd><p>A <code><gdb:iterator></code> object is constructed with the <code>make-iterator</code>
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procedure. It takes three arguments: the object to be iterated over,
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an object to record the progress of the iteration, and a procedure to
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return the next element in the iteration, or an implementation chosen value
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to denote the end of iteration.
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</p>
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<p>By convention, end of iteration is marked with <code>(end-of-iteration)</code>,
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and may be tested with the <code>end-of-iteration?</code> predicate.
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The result of <code>(end-of-iteration)</code> is chosen so that it is not
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otherwise used by the <code>(gdb)</code> module. If you are using
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<code><gdb:iterator></code> in your own code it is your responsibility to
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maintain this invariant.
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</p>
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<p>A trivial example for illustration’s sake:
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</p>
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<div class="smallexample">
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<pre class="smallexample">(use-modules (gdb iterator))
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(define my-list (list 1 2 3))
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(define iter
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(make-iterator my-list my-list
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(lambda (iter)
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(let ((l (iterator-progress iter)))
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(if (eq? l '())
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(end-of-iteration)
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(begin
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(set-iterator-progress! iter (cdr l))
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(car l)))))))
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</pre></div>
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<p>Here is a slightly more realistic example, which computes a list of all the
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functions in <code>my-global-block</code>.
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</p>
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<div class="smallexample">
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<pre class="smallexample">(use-modules (gdb iterator))
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(define this-sal (find-pc-line (frame-pc (selected-frame))))
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(define this-symtab (sal-symtab this-sal))
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(define this-global-block (symtab-global-block this-symtab))
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(define syms-iter (make-block-symbols-iterator this-global-block))
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(define functions (iterator-filter symbol-function? syms-iter))
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</pre></div>
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</dd></dl>
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<dl>
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<dt><a name="index-iterator_003f"></a>Scheme Procedure: <strong>iterator?</strong> <em>object</em></dt>
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<dd><p>Return <code>#t</code> if <var>object</var> is a <code><gdb:iterator></code> object.
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Otherwise return <code>#f</code>.
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</p></dd></dl>
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<dl>
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<dt><a name="index-iterator_002dobject"></a>Scheme Procedure: <strong>iterator-object</strong> <em>iterator</em></dt>
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<dd><p>Return the first argument that was passed to <code>make-iterator</code>.
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This is the object being iterated over.
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</p></dd></dl>
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<dl>
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<dt><a name="index-iterator_002dprogress"></a>Scheme Procedure: <strong>iterator-progress</strong> <em>iterator</em></dt>
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<dd><p>Return the object tracking iteration progress.
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</p></dd></dl>
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<dl>
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<dt><a name="index-set_002diterator_002dprogress_0021"></a>Scheme Procedure: <strong>set-iterator-progress!</strong> <em>iterator new-value</em></dt>
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<dd><p>Set the object tracking iteration progress.
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</p></dd></dl>
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<dl>
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<dt><a name="index-iterator_002dnext_0021"></a>Scheme Procedure: <strong>iterator-next!</strong> <em>iterator</em></dt>
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<dd><p>Invoke the procedure that was the third argument to <code>make-iterator</code>,
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passing it one argument, the <code><gdb:iterator></code> object.
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The result is either the next element in the iteration, or an end
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marker as implemented by the <code>next!</code> procedure.
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By convention the end marker is the result of <code>(end-of-iteration)</code>.
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</p></dd></dl>
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<dl>
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<dt><a name="index-end_002dof_002diteration"></a>Scheme Procedure: <strong>end-of-iteration</strong></dt>
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<dd><p>Return the Scheme object that denotes end of iteration.
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</p></dd></dl>
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<dl>
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<dt><a name="index-end_002dof_002diteration_003f"></a>Scheme Procedure: <strong>end-of-iteration?</strong> <em>object</em></dt>
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<dd><p>Return <code>#t</code> if <var>object</var> is the end of iteration marker.
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Otherwise return <code>#f</code>.
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</p></dd></dl>
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<p>These functions are provided by the <code>(gdb iterator)</code> module to
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assist in using iterators.
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</p>
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<dl>
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<dt><a name="index-make_002dlist_002diterator"></a>Scheme Procedure: <strong>make-list-iterator</strong> <em>list</em></dt>
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<dd><p>Return a <code><gdb:iterator></code> object that will iterate over <var>list</var>.
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</p></dd></dl>
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<dl>
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<dt><a name="index-iterator_002d_003elist"></a>Scheme Procedure: <strong>iterator->list</strong> <em>iterator</em></dt>
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<dd><p>Return the elements pointed to by <var>iterator</var> as a list.
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</p></dd></dl>
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<dl>
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<dt><a name="index-iterator_002dmap"></a>Scheme Procedure: <strong>iterator-map</strong> <em>proc iterator</em></dt>
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<dd><p>Return the list of objects obtained by applying <var>proc</var> to the object
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pointed to by <var>iterator</var> and to each subsequent object.
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</p></dd></dl>
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<dl>
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<dt><a name="index-iterator_002dfor_002deach"></a>Scheme Procedure: <strong>iterator-for-each</strong> <em>proc iterator</em></dt>
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<dd><p>Apply <var>proc</var> to each element pointed to by <var>iterator</var>.
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The result is unspecified.
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</p></dd></dl>
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<dl>
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<dt><a name="index-iterator_002dfilter"></a>Scheme Procedure: <strong>iterator-filter</strong> <em>pred iterator</em></dt>
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<dd><p>Return the list of elements pointed to by <var>iterator</var> that satisfy
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<var>pred</var>.
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</p></dd></dl>
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<dl>
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<dt><a name="index-iterator_002duntil"></a>Scheme Procedure: <strong>iterator-until</strong> <em>pred iterator</em></dt>
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<dd><p>Run <var>iterator</var> until the result of <code>(pred element)</code> is true
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and return that as the result. Otherwise return <code>#f</code>.
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</p></dd></dl>
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<div class="header">
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<p>
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Previous: <a href="Memory-Ports-in-Guile.html#Memory-Ports-in-Guile" accesskey="p" rel="previous">Memory Ports in Guile</a>, Up: <a href="Guile-API.html#Guile-API" accesskey="u" rel="up">Guile API</a> [<a href="index.html#SEC_Contents" title="Table of contents" rel="contents">Contents</a>][<a href="Concept-Index.html#Concept-Index" title="Index" rel="index">Index</a>]</p>
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