<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 3.2//EN"> <HTML> <HEAD> <TITLE>Programming in XPCE/Prolog</TITLE><LINK REL=home HREF="index.html"> <LINK REL=contents HREF="Contents.html"> <LINK REL=index HREF="DocIndex.html"> <LINK REL=summary HREF="summary.html"> <LINK REL=previous HREF="summary.html"> <LINK REL=next HREF="DocIndex.html"> </HEAD> <BODY BGCOLOR="white"> <HR> <CENTER> <A HREF="index.html"><IMG SRC="home.gif" BORDER=0 ALT="Home"></A> <A HREF="Contents.html"><IMG SRC="index.gif" BORDER=0 ALT="Contents"></A> <A HREF="DocIndex.html"><IMG SRC="yellow_pages.gif" BORDER=0 ALT="Index"></A> <A HREF="summary.html"><IMG SRC="info.gif" BORDER=0 ALT="Summary"></A> <A HREF="summary.html"><IMG SRC="prev.gif" BORDER=0 ALT="Previous"></A> <A HREF="DocIndex.html"><IMG SRC="next.gif" BORDER=0 ALT="Next"></A> </CENTER> <HR> <H1><A NAME="document-notes">Footnotes</A></H1> <DL> <P> <DT><A NAME=note-1 HREF="sec-2.2.html#back-to-note-1">note-1</A><DD> Normal applications use almost exclusively <font size=-1>XPCE</font> generated references. Many of the examples in this manual are typed from the terminal and Prolog specified references are easier to type. <DT><A NAME=note-2 HREF="sec-2.2.html#back-to-note-2">note-2</A><DD> The attributes of an object state are called slots. In other languages they may be called <EM>instance variables</EM> or fields. <DT><A NAME=note-3 HREF="sec-2.2.html#back-to-note-3">note-3</A><DD> Prolog would normally print `<A NAME="idx:display:875"></A><B>@display</B>'. The <CODE>library(pce_portray)</CODE> defines a clause for the Prolog predicate <A NAME="idx:portray1:876"></A><B>portray/1</B> that prints object references as `<A NAME="idx:Reference:877"></A><B>@Reference</B>/Class'. This library is used throughout all the examples of this manual. <DT><A NAME=note-4 HREF="fileviewer.html#back-to-note-4">note-4</A><DD> Initial versions of <font size=-1>XPCE</font> lacked the obtainer. In this case the browser <EM>B</EM> would be passed to the predicate <A NAME="idx:view1:878"></A><B>view/1</B>, which would extract the current filename from the browser. Obtainers improve the readability and avoid the need to mix UI related code with application code. <DT><A NAME=note-5 HREF="fileviewer.html#back-to-note-5">note-5</A><DD> This conversion is implemented with class <A HREF="summary.html#class:dict_item">dict_item</A>. In fact, the browser just specifies the desired type and the message passing kernel invokes the conversion method of class <A HREF="summary.html#class:dict_item">dict_item</A>. <DT><A NAME=note-6 HREF="sec-3.3.html#back-to-note-6">note-6</A><DD> Given the dynamic nature of delegation, the system cannot possibly determine all methods available through delegation. Consider a slot specified with type <A HREF="summary.html#class:graphical">graphical</A>. The system can infer it will surely be able to use behaviour defined at class <A HREF="summary.html#class:graphical">graphical</A>. If at runtime, the slot is filled with a <A HREF="summary.html#class:box">box</A>, all methods defined at class box will be available too. <DT><A NAME=note-7 HREF="notprolog.html#back-to-note-7">note-7</A><DD> This example uses <font size=-1>XPCE</font> user-defined classes. The details of this mechanism do not matter for the argument in this section. User-defined classes are described in <A HREF="udc.html">chapter 7</A>. <DT><A NAME=note-8 HREF="udc.html#back-to-note-8">note-8</A><DD> <font size=-1>XPCE</font> defines four implementation techniques for methods. <EM>C-function pointers</EM> are used for almost all the built-in behaviour. <EM>C++-function pointers</EM> are used when classes are defined in C++ (<CITE><A HREF="Bibliography.html#XPCE:cpp">Wielemaker & Anjewierden, 1994</A></CITE>) . Instances of <A HREF="summary.html#class:c_pointer">c_pointer</A> are left to the host object for interpretation and finally, <A HREF="summary.html#class:code">code</A> objects are executed. <DT><A NAME=note-9 HREF="sec-7.1.html#back-to-note-9">note-9</A><DD> Value must be an int, name or <A HREF="summary.html#class:constant">constant</A> in the current implementation. <DT><A NAME=note-10 HREF="sec-7.5.html#back-to-note-10">note-10</A><DD> To facilitate the translation of old code, the construct <TT>:- send(<A NAME="idx:class:879"></A><B>@class</B>, ...</TT> is treated automatically as if it was embedded using <A NAME="idx:pceclassdirective1:880"></A><A HREF="sec-7.1.html#pce_class_directive/1">pce_class_directive/1</A> <DT><A NAME=note-11 HREF="classvar.html#back-to-note-11">note-11</A><DD> On Windows systems, <CODE>~</CODE> expands to <CODE>\%HOME\%</CODE>, <CODE>\%USERPROFILE\%</CODE>, <CODE>\%HOMEDRIVE\%/\%HOMEPATH\%</CODE> or the root of the current drive. See <A NAME="idx:expandfilename2:881"></A><B>expand_file_name/2</B> of the SWI-Prolog manual. <DT><A NAME=note-12 HREF="font.html#back-to-note-12">note-12</A><DD> See <A HREF="classvar.html">section 8</A> for the default syntax. <DT><A NAME=note-13 HREF="dragdrop.html#back-to-note-13">note-13</A><DD> Attach a <B>drag_and_drop_dict_item_gesture</B> to a <A HREF="summary.html#class:list_browser">list_browser</A> to enable dragging the items in the dictionary <DT><A NAME=note-14 HREF="httpd.html#back-to-note-14">note-14</A><DD> Using the Unix/X11 version <font size=-1>XPCE</font> can manage windows on multiple desktops. For MS-Windows users this is not supported. <DT><A NAME=note-15 HREF="vishierarchy.html#back-to-note-15">note-15</A><DD> To remember this sequence: <B>V</B> for Visual and all defined modifiers to avoid a conflict with application defined key-bindings. <DT><A NAME=note-16 HREF="sec-C.2.html#back-to-note-16">note-16</A><DD> We will mix the terms <EM>instance</EM> and <EM>object</EM> freely in this document. They are considered synonyms. <DT><A NAME=note-17 HREF="sec-C.2.html#back-to-note-17">note-17</A><DD> Class class is an instance of itself. In other systems (SmallTalk, <CITE><A HREF="Bibliography.html#Goldberg:83a">Goldberg & Robson, 1983</A></CITE>), classes are instances of a <EM>meta-class</EM>. Yet in other systems, classes have a completely different status (for example widgets in the X11 Intrinsics) <DT><A NAME=note-18 HREF="sec-C.2.html#back-to-note-18">note-18</A><DD> Multiple inheritance introduces various technical and conceptual problems. <font size=-1>XPCE</font> uses delegation and templates to achieve similar results. This is explained in <A HREF="delegation.html">section C.4</A> and <A HREF="sec-7.5.html">section 7.5.2.1</A>. <DT><A NAME=note-19 HREF="sec-E.1.html#back-to-note-19">note-19</A><DD> PCE assumes the object has become a <EM>support</EM> object. This is generally not correct for code objects. Class <A HREF="summary.html#class:code">code</A> therefore has <A NAME="idx:classgetunanswer:882"></A>`<B>class<CODE><-</CODE>un_answer</B>: <A NAME="idx:off:883"></A><B>@off</B>', which implies that objects that fill a slot of a code object will not loose their `answer' status. <DT><A NAME=note-20 HREF="trouble.html#back-to-note-20">note-20</A><DD> A `ground' term is a Prolog term that has no unbound variables. <DT><A NAME=note-21 HREF="summary.html#back-to-note-21">note-21</A><DD> Colour screens create their colour by mixing the `primary' colours `red', `green' and `blue'. With an `RBG' triple, we refer to a triple of three numeric values representing the intensities of the three primary colours </DL> </BODY></HTML>
