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<H2><A NAME="sec:D.2"><SPAN class="sec-nr">D.2</SPAN> <SPAN class="sec-title">Additional 
interface libraries</SPAN></A></H2>

<P><A NAME="idx:autoloading:689"></A>This section describes Some of the 
predicates available from the
<font size=-1>XPCE</font>/Prolog library.

<H3><A NAME="sec:D.2.1"><SPAN class="sec-nr">D.2.1</SPAN> <SPAN class="sec-title">Library 
``pce_util''</SPAN></A></H3>

<P>The predicates in this section used to be <font size=-1>XPCE</font> 
principal predicates. Changes to <font size=-1>XPCE</font>, the 
interface and our current understanding about programming the <font size=-1>XPCE</font>/Prolog 
environment have made these predicates less important.

<DL>
<DT class="pubdef"><A NAME="send_list/2,3"><STRONG>send_list</STRONG>(<VAR>+Receiver, 
+Selector [, +Argument]</VAR>)</A></DT>
<DD class="defbody">
Invoke send-behaviour as <A NAME="idx:send212:690"></A><A class="pred" href="sec-7.1.html#send/[2-12]">send/[2-12]</A>. 
Each of the arguments is either as accepted by <A NAME="idx:send212:691"></A><A class="pred" href="sec-7.1.html#send/[2-12]">send/[2-12]</A> 
or a list of such arguments. The definition of <A NAME="idx:sendlist2:692"></A><SPAN class="pred-ext">send_list/2</SPAN> 
is below.

<PRE class="code">
send_list([], _) :- !.
send_list(_, []) :- !.
send_list([Object|Objects], Selectors) :- !, 
        send_list(Object, Selectors), 
        send_list(Objects, Selectors).
send_list(Object, [Selector|Selectors]) :- !, 
        send_list(Object, Selector), 
        send_list(Object, Selectors).
send_list(Object, Selector) :-
        send(Object, Selector).
</PRE>

<P>Note that, since <A NAME="idx:send2:693"></A><A class="pred" href="sec-D.1.html#send/2">send/2</A> 
accepts <CODE>Selector(Arg...)</CODE> the following is now valid code:

<PRE class="code">
        ...,
        send_list(Box,
                  [ colour(red),
                    fill_pattern(colour(greed))
                  ]),
</PRE>

</DD>
<DT class="pubdef"><A NAME="get_object/[3-13]"><STRONG>get_object</STRONG>(<VAR>+Receiver, 
+Selector, +Argument..., -Result</VAR>)</A></DT>
<DD class="defbody">
Equivalent to <A NAME="idx:get313:694"></A><A class="pred" href="sec-D.1.html#get/3">get/[3-13]</A>, 
but instead of unifying a variable with a reference the variable is 
unified with the term-description. The arguments are unified as in <A NAME="idx:get313:695"></A><A class="pred" href="sec-D.1.html#get/3">get/[3-13]</A>. 
Normally only used from the Prolog top level for debugging purposes.</DD>
<DT class="pubdef"><A NAME="chain_list/2"><STRONG>chain_list</STRONG>(<VAR>?Chain, 
?List</VAR>)</A></DT>
<DD class="defbody">
Converts between a <font size=-1>XPCE</font> chain and a Prolog list. 
This may be useful to exploit Prolog's list-processing primitives. Note 
however that <font size=-1>XPCE</font> chains define various operations 
that may be exploited to avoid the translation. Suppose `Pict' is a 
picture and `Pos' is a point object. We want to determine the topmost 
graphical object overlapping with `Pos'. The following two programs are 
identical:

<PRE class="code">
topmost_graphical(Pict, Pos, Gr) :-
        get(Pict, graphicals, Grs0),
        chain_list(Grs0, Grs1),
        topmost(Grs1, Pos, @nil, Gr),
        Gr \== @nil.

topmost([], _, Gr, Gr).
topmost([H|T], Pos, _, Gr) :-
        send(H, overlap, Pos), !,
        topmost(T, Pos, H, Gr).
topmost([_|T], Pos, Gr0, Gr) :-
        topmost(T, Pos, Gr0, Gr).
</PRE>

<P>Or, using <font size=-1>XPCE</font>'s list processing:

<PRE class="code">
topmost_graphical(Dev, Pos, Gr) :-
        get(Dev, graphicals, Grs),
        get(Grs, find_all,
            message(@arg1, overlap, Pos), O),
        get(O, tail, Gr),
        send(O, done).
</PRE>

<P>The second implementation is not only shorter, it also requires far 
less data conversions between Prolog and <font size=-1>XPCE</font> and 
is therefore much faster.</DD>
<DT class="pubdef"><A NAME="get_chain/3"><STRONG>get_chain</STRONG>(<VAR>+Receiver, 
+Selector, -List</VAR>)</A></DT>
<DD class="defbody">
Utility predicate implemented as:

<PRE class="code">
get_chain(Receiver, Selector, List) :-
        get(Receiver, Selector, Chain),
        chain_list(Chain, List).
</PRE>

<P>See comments with <A NAME="idx:chainlist2:696"></A><A class="pred" href="sec-D.2.html#chain_list/2">chain_list/2</A>.
</DD>
</DL>

<H3><A NAME="sec:D.2.2"><SPAN class="sec-nr">D.2.2</SPAN> <SPAN class="sec-title">Library 
``pce_debug''</SPAN></A></H3>

<P>The predicates in this section provide shorthands for common commands 
for debugging <font size=-1>XPCE</font> programs. See <A class="sec" href="debugging.html">section 
12</A> for more information on debugging <font size=-1>XPCE/P</font>rolog 
programs.

<DL>
<DT class="pubdef"><A NAME="tracepce/1"><STRONG>tracepce</STRONG>(<VAR>+Class <TT>&lt;-|-&gt;|-</TT> 
Selector</VAR>)</A></DT>
<DD class="defbody">
Find send- (<CODE>-&gt;</CODE>), get- (<CODE>&lt;-</CODE>) method or 
variable (<CODE>-</CODE>) and cause invocations thereof to be printed on 
the console.

<P>Syntax note: (<CODE>-&gt;</CODE>) is a standard Prolog operator with
<VAR>priority &gt; 1000</VAR>. Therefore many Prolog systems require 
additional brackets:

<PRE class="code">
1 ?- tracepce((graphical -&gt;selected)).
</PRE>

<P>In SWI-Prolog this is not necessary. To be able to trace get-methods 
with this predicate (<CODE>&lt;-</CODE>) must be declared as an infix 
operator.</DD>
<DT class="pubdef"><A NAME="notracepce/1"><STRONG>notracepce</STRONG>(<VAR>+Class <TT>&lt;-|-&gt;|-</TT> 
Selector</VAR>)</A></DT>
<DD class="defbody">
Disables trace-point set with <A NAME="idx:tracepce1:697"></A><A class="pred" href="sec-D.2.html#tracepce/1">tracepce/1</A>.</DD>
<DT class="pubdef"><A NAME="checkpce/0"><STRONG>checkpce</STRONG></A></DT>
<DD class="defbody">
Collect all global (named-) objects and run <A NAME="idx:objectsendcheck:698"></A>`<B>object<CODE>-&gt;</CODE>_check</B>' 
on them. This performs various consistency checks on the objects and 
prints diagnostic messages if something is wrong. <A NAME="idx:objectsendcheck:699"></A>`<B>object<CODE>-&gt;</CODE>_check</B>' 
checks all objects it can (recursively) find through slot-references, 
chains, vectors and hash-tables and deals properly with loops in the 
data-structure.
</DD>
<DT class="pubdef"><A NAME="show_slots/1"><STRONG>show_slots</STRONG>(<VAR>+Reference</VAR>)</A></DT>
<DD class="defbody">
Prints the values of all instance variables of <VAR>Reference</VAR>:

<PRE class="code">
1 ?- new(@move_gesture, move_gesture).
2 ?- show_slots(@move_gesture).
@move_gesture/move_gesture
        active                @on/bool
        button                middle
        modifier              @810918/modifier
        condition             @nil/constant
        status                inactive
        cursor                @default/constant
        offset                @548249/point
</PRE>

<P>A graphical tool for inspecting instance variables is described in
<A class="sec" href="inspector.html">section 12.5</A>.
</DD>
</DL>

<H3><A NAME="sec:D.2.3"><SPAN class="sec-nr">D.2.3</SPAN> <SPAN class="sec-title">Accessing 
the <font size=-1>XPCE</font> manual</SPAN></A></H3>

<A NAME="sec:manpce"></A>

<DL>
<DT class="pubdef"><A NAME="manpce/0"><STRONG>manpce</STRONG></A></DT>
<DD class="defbody">
Start the <font size=-1>XPCE</font> online manual tools. This opens a 
small GUI console at the top-left of the screen, providing access to the 
manual, demo programs and tools described in this manual. See <A class="sec" href="online.html">chapter 
3</A>.</DD>
<DT class="pubdef"><A NAME="manpce/1"><STRONG>manpce</STRONG>(<VAR>+Spec</VAR>)</A></DT>
<DD class="defbody">
As <A NAME="idx:manpce0:700"></A><A class="pred" href="sec-D.2.html#manpce/0">manpce/0</A>, 
but immediately opens the the manual from <VAR>Spec</VAR>.
<VAR>Spec</VAR> is either a class-name, opening the ClassBrowser, or a 
term Class <TT>&lt;-|-&gt;|-</TT> Selector (see <A NAME="idx:tracepce1:701"></A><A class="pred" href="sec-D.2.html#tracepce/1">tracepce/1</A>) 
to open the manual-card of the specified behaviour. Examples:

<PRE class="code">
1 ?- manpce(box).
2 ?- manpce((view-&gt;caret)).
</PRE>

<P></DD>
</DL>

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