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<a name="Iterators-In-Guile"></a>
<div class="header">
<p>
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</div>
<hr>
<a name="Iterators-In-Guile-1"></a>
<h4 class="subsubsection">23.3.3.25 Iterators In Guile</h4>

<a name="index-guile-iterators"></a>
<a name="index-_003cgdb_003aiterator_003e"></a>

<p>A simple iterator facility is provided to allow, for example,
iterating over the set of program symbols without having to first
construct a list of all of them.  A useful contribution would be
to add support for SRFI 41 and SRFI 45.
</p>
<dl>
<dt><a name="index-make_002diterator"></a>Scheme Procedure: <strong>make-iterator</strong> <em>object progress next!</em></dt>
<dd><p>A <code>&lt;gdb:iterator&gt;</code> object is constructed with the <code>make-iterator</code>
procedure.  It takes three arguments: the object to be iterated over,
an object to record the progress of the iteration, and a procedure to
return the next element in the iteration, or an implementation chosen value
to denote the end of iteration.
</p>
<p>By convention, end of iteration is marked with <code>(end-of-iteration)</code>,
and may be tested with the <code>end-of-iteration?</code> predicate.
The result of <code>(end-of-iteration)</code> is chosen so that it is not
otherwise used by the <code>(gdb)</code> module.  If you are using
<code>&lt;gdb:iterator&gt;</code> in your own code it is your responsibility to
maintain this invariant.
</p>
<p>A trivial example for illustration&rsquo;s sake:
</p>
<div class="smallexample">
<pre class="smallexample">(use-modules (gdb iterator))
(define my-list (list 1 2 3))
(define iter
  (make-iterator my-list my-list
                 (lambda (iter)
                   (let ((l (iterator-progress iter)))
                     (if (eq? l '())
                         (end-of-iteration)
                         (begin
                           (set-iterator-progress! iter (cdr l))
                           (car l)))))))
</pre></div>

<p>Here is a slightly more realistic example, which computes a list of all the
functions in <code>my-global-block</code>.
</p>
<div class="smallexample">
<pre class="smallexample">(use-modules (gdb iterator))
(define this-sal (find-pc-line (frame-pc (selected-frame))))
(define this-symtab (sal-symtab this-sal))
(define this-global-block (symtab-global-block this-symtab))
(define syms-iter (make-block-symbols-iterator this-global-block))
(define functions (iterator-filter symbol-function? syms-iter))
</pre></div>
</dd></dl>

<dl>
<dt><a name="index-iterator_003f"></a>Scheme Procedure: <strong>iterator?</strong> <em>object</em></dt>
<dd><p>Return <code>#t</code> if <var>object</var> is a <code>&lt;gdb:iterator&gt;</code> object.
Otherwise return <code>#f</code>.
</p></dd></dl>

<dl>
<dt><a name="index-iterator_002dobject"></a>Scheme Procedure: <strong>iterator-object</strong> <em>iterator</em></dt>
<dd><p>Return the first argument that was passed to <code>make-iterator</code>.
This is the object being iterated over.
</p></dd></dl>

<dl>
<dt><a name="index-iterator_002dprogress"></a>Scheme Procedure: <strong>iterator-progress</strong> <em>iterator</em></dt>
<dd><p>Return the object tracking iteration progress.
</p></dd></dl>

<dl>
<dt><a name="index-set_002diterator_002dprogress_0021"></a>Scheme Procedure: <strong>set-iterator-progress!</strong> <em>iterator new-value</em></dt>
<dd><p>Set the object tracking iteration progress.
</p></dd></dl>

<dl>
<dt><a name="index-iterator_002dnext_0021"></a>Scheme Procedure: <strong>iterator-next!</strong> <em>iterator</em></dt>
<dd><p>Invoke the procedure that was the third argument to <code>make-iterator</code>,
passing it one argument, the <code>&lt;gdb:iterator&gt;</code> object.
The result is either the next element in the iteration, or an end
marker as implemented by the <code>next!</code> procedure.
By convention the end marker is the result of <code>(end-of-iteration)</code>.
</p></dd></dl>

<dl>
<dt><a name="index-end_002dof_002diteration"></a>Scheme Procedure: <strong>end-of-iteration</strong></dt>
<dd><p>Return the Scheme object that denotes end of iteration.
</p></dd></dl>

<dl>
<dt><a name="index-end_002dof_002diteration_003f"></a>Scheme Procedure: <strong>end-of-iteration?</strong> <em>object</em></dt>
<dd><p>Return <code>#t</code> if <var>object</var> is the end of iteration marker.
Otherwise return <code>#f</code>.
</p></dd></dl>

<p>These functions are provided by the <code>(gdb iterator)</code> module to
assist in using iterators.
</p>
<dl>
<dt><a name="index-make_002dlist_002diterator"></a>Scheme Procedure: <strong>make-list-iterator</strong> <em>list</em></dt>
<dd><p>Return a <code>&lt;gdb:iterator&gt;</code> object that will iterate over <var>list</var>.
</p></dd></dl>

<dl>
<dt><a name="index-iterator_002d_003elist"></a>Scheme Procedure: <strong>iterator-&gt;list</strong> <em>iterator</em></dt>
<dd><p>Return the elements pointed to by <var>iterator</var> as a list.
</p></dd></dl>

<dl>
<dt><a name="index-iterator_002dmap"></a>Scheme Procedure: <strong>iterator-map</strong> <em>proc iterator</em></dt>
<dd><p>Return the list of objects obtained by applying <var>proc</var> to the object
pointed to by <var>iterator</var> and to each subsequent object.
</p></dd></dl>

<dl>
<dt><a name="index-iterator_002dfor_002deach"></a>Scheme Procedure: <strong>iterator-for-each</strong> <em>proc iterator</em></dt>
<dd><p>Apply <var>proc</var> to each element pointed to by <var>iterator</var>.
The result is unspecified.
</p></dd></dl>

<dl>
<dt><a name="index-iterator_002dfilter"></a>Scheme Procedure: <strong>iterator-filter</strong> <em>pred iterator</em></dt>
<dd><p>Return the list of elements pointed to by <var>iterator</var> that satisfy
<var>pred</var>.
</p></dd></dl>

<dl>
<dt><a name="index-iterator_002duntil"></a>Scheme Procedure: <strong>iterator-until</strong> <em>pred iterator</em></dt>
<dd><p>Run <var>iterator</var> until the result of <code>(pred element)</code> is true
and return that as the result.  Otherwise return <code>#f</code>.
</p></dd></dl>

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