/usr/lib/swi-prolog/doc/Manual/guitracer.html

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<h2 id="sec:guitracer"><a id="sec:3.5"><span class="sec-nr">3.5</span> <span class="sec-title">The 
Graphical Debugger</span></a></h2>

<a id="sec:guitracer"></a>

<p>SWI-Prolog offers two debuggers. One is the traditional text 
console-based 4-port Prolog tracer and the other is a window-based 
source level debugger. The window-based debugger requires XPCE 
installed. It operates based on the <a id="idx:prologtraceinterception4:282"></a><a class="pred" href="tracehook.html#prolog_trace_interception/4">prolog_trace_interception/4</a> 
hook and other low-level functionality described in <a class="sec" href="hack.html">chapter 
B</a>.

<p>Window-based tracing provides a much better overview due to the 
eminent relation to your source code, a clear list of named variables 
and their bindings as well as a graphical overview of the call and 
choice point stack. There are some drawbacks though. Using a textual 
trace on the console, one can scroll back and examine the past, while 
the graphical debugger just presents a (much better) overview of the 
current state.

<p><h3 id="sec:start-guitracer"><a id="sec:3.5.1"><span class="sec-nr">3.5.1</span> <span class="sec-title">Invoking 
the window-based debugger</span></a></h3>

<a id="sec:start-guitracer"></a>

<p>Whether the text-based or window-based debugger is used is controlled 
using the predicates <a id="idx:guitracer0:283"></a><a class="pred" href="guitracer.html#guitracer/0">guitracer/0</a> 
and <a id="idx:noguitracer0:284"></a><a class="pred" href="guitracer.html#noguitracer/0">noguitracer/0</a>. 
Entering debug mode is controlled using the normal predicates for this: <a id="idx:trace0:285"></a><a class="pred" href="debugger.html#trace/0">trace/0</a> 
and
<a id="idx:spy1:286"></a><a class="pred" href="debugger.html#spy/1">spy/1</a>. 
In addition, PceEmacs prolog mode provides the command
<strong>Prolog/Break at</strong> (<code>Control-c b</code>) to insert a 
break-point at a specific location in the source code.

<p>The graphical tracer is particulary useful for debugging threads. The 
tracer must be loaded from the <code>main</code> thread before it can be 
used from a background thread.

<dl class="latex">
<dt class="pubdef"><a id="guitracer/0"><strong>guitracer</strong></a></dt>
<dd class="defbody">
This predicate installs the above-mentioned hooks that redirect tracing 
to the window-based environment. No window appears. The debugger window 
appears as actual tracing is started through <a id="idx:trace0:287"></a><a class="pred" href="debugger.html#trace/0">trace/0</a>, 
by hitting a spy point defined by <a id="idx:spy1:288"></a><a class="pred" href="debugger.html#spy/1">spy/1</a> 
or a break point defined using the PceEmacs command <strong>Prolog/Break 
at</strong> (<code>Control-c b</code>).</dd>
<dt class="pubdef"><a id="noguitracer/0"><strong>noguitracer</strong></a></dt>
<dd class="defbody">
Disable the hooks installed by <a id="idx:guitracer0:289"></a><a class="pred" href="guitracer.html#guitracer/0">guitracer/0</a>, 
reverting to normal text console-based tracing.</dd>
<dt class="pubdef"><a id="gtrace/0"><strong>gtrace</strong></a></dt>
<dd class="defbody">
Utility defined as <code>guitracer,trace</code>.</dd>
<dt class="pubdef"><a id="gdebug/0"><strong>gdebug</strong></a></dt>
<dd class="defbody">
Utility defined as <code>guitracer,debug</code>.</dd>
<dt class="pubdef"><a id="gspy/1"><strong>gspy</strong>(<var>+Predicate</var>)</a></dt>
<dd class="defbody">
Utility defined as <code>guitracer,spy(Predicate)</code>.
</dd>
</dl>

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swi-prolog-nox 6.6.4-2ubuntu1 / usr / lib / swi-prolog / doc / Manual / guitracer.html
