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79 lines
3.4 KiB
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79 lines
3.4 KiB
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<title>Logtalk built-in predicate: threaded_peek/1-2</title>
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<div class="top-left">Logtalk reference manual</div>
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<div class="top-right">Built-in predicate: threaded_peek/1-2</div>
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<div class="bottom-left"><span class="page"/></div>
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<div class="bottom-right"><span class="page"/></div>
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<div class="navtop"><a href="../../index.html">contents</a> > <a href="../index.html">reference manual</a> > <a href="../index.html#builtins">built-in predicates</a></div>
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<h2 id="builtins_threaded_peek1_2" class="codenp">threaded_peek/1-2</h2>
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<h4>Description</h4>
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<pre>threaded_peek(Goal)
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threaded_peek(Goal, Tag)</pre>
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<p>
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Checks if the result of proving <code>Goal</code> in a new thread is already available. This call succeeds or fails without blocking execution waiting for a reply to be available.
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</p>
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<p>
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The argument of this predicate should be a <em>variant</em> of the argument of the corresponding <a href="threaded_call1_2.html">threaded_call/1</a> call. When the predicate argument is subsumed by the <a href="threaded_call1_2.html">threaded_call/1</a> call argument, the <code>threaded_peek/1</code> call will succeed iff its argument unifies with an already available solution of the (more general) goal.
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</p>
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<p>
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The variant <code>threaded_peek/2</code> accepts a threaded call identifier tag generated by the calls to the <a title="Consult reference manual" href="threaded_call1_2.html"><code>threaded_call/2</code></a> and <a title="Consult reference manual" href="threaded_once1_2.html"><code>threaded_once/2</code></a> predicates. Tags shall be considered as an opaque term; users shall not rely on its type.
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</p>
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<h4>Template and modes</h4>
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<pre>threaded_peek(+callable)
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threaded_peek(+callable, +nonvar)</pre>
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<h4>Errors</h4>
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<dl>
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<dt>Goal is a variable:</dt>
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<dd><code>instantiation_error</code></dd>
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<dt>Goal is neither a variable nor a callable term:</dt>
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<dd><code>type_error(callable, Goal)</code></dd>
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<dt>Tag is a variable:</dt>
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<dd><code>instantiation_error</code></dd>
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</dl>
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<h4>Examples</h4>
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<dl>
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<dt>To check for an asynchronous goal proof result:</dt>
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<dd><code>threaded_peek(Goal)</code></dd>
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<dt>To check for an asynchronous message to <em>self</em> result:</dt>
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<dd><code>threaded_peek(::Goal)</code></dd>
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<dt>To check for an asynchronous message result:</dt>
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<dd><code>threaded_peek(Object::Goal)</code></dd>
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</dl>
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<div class="footer">
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<div class="copyright">
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<span>Copyright © <a href="mailto:pmoura@logtalk.org">Paulo Moura</a> — <a href="http://logtalk.org">Logtalk.org</a></span><br/>
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<span>Last updated on: September 15, 2007</span>
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