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Debugging messages
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<H3 CLASS="subsection"><A NAME="htoc26">4.4</A> Debugging messages</H3>
We here described which information is displayed by the debugger when it
shows a goal. The basic format is as follows:
<DL CLASS="list" COMPACT="compact"><DT CLASS="dt-list"><DD CLASS="dd-list"><TT><I>S N M Port</I>: <I>Goal</I> ?</TT></DL><I><TT>
S</TT></I> is a spy-point indicator: if there is a spy-point on the
current goal the <TT>+</TT> symbol is displayed else a space is displayed.
<I><TT>N</TT></I> is the invocation number. This unique number can be used
to correlate the trace messages for the various ports, since it is unique
for every invocation. <I><TT>M</TT></I> is an index number which
represents the number of direct ancestors of the goal (i.e. the current
depth of the goal). <I><TT>Port</TT></I> specifies the particular port
(<TT>call</TT>, <TT>exit</TT>, <TT>fail</TT>, <TT>redo</TT>,
<TT>exception</TT>). <I><TT>Goal</TT></I> is the current goal (it is then
possible to inspect its current instantiation) which is displayed using
<TT>write_term/3</TT> with <TT>quoted(true)</TT> and
<TT>max_depth(<I>D</I>)</TT> options (section <A HREF="gprolog037.html#write-term/3">7.14.6</A>). Initially
<I><TT>D</TT></I> (the print depth) is set to 10 but can be redefined
using the <TT><</TT> debugger command (section <A HREF="gprolog014.html#Debugger-commands">4.5</A>). The
<TT>?</TT> symbol is displayed when the debugger is waiting a command from
the user. (i.e. <TT>Port</TT> is a leashed port). If the port is unleashed,
this symbol is not displayed and the debugger continues the execution
displaying the next goal.<BR>
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Copyright (C) 1999-2007 Daniel Diaz
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