\chapter{Introduction}

This document provides course-notes and exercises for programming in
XPCE/Prolog.  Some basic knowledge of Prolog is assumed.  XPCE
provides the following subsystems.

\begin{itemize}
\tick{Primitives for building a GUI}  Graphical user interfaces are
complicated systems.  They potentionally consist of a large number of
different (visual) entities, possibly with complicated interrelations.
XPCE provides high-level building blocks for building dialog windows
and interactive graphical representations as well as the dynamics
thereof.

\tick{The Object System} The object system of XPCE allows the user to create,
manipulate, query and destroy objects.  XPCE objects represent, in
addition to GUI components, various data representation primitives,
classes (for defining and extending XPCE) and executable objects for
relating GUI components to each other and the application.

\tick{The Unix process and filesystem} These building blocks allow
the user to communicate to the rest of the computing environment.

\tick{Debugging and statistics} Tools allow the user to analyse
the GUI as well as tracing the dynamic behaviour of GUI's.
\end{itemize}


XPCE is both a very large library and a programming environment in its
own right.  XPCE has similar problems as other big systems such as
SmallTalk, CommonLisp, GNU-Emacs and the Unix Tool Kit.  All of these
environments are hard to master, just because they provide a virtually
enless collection of built-in behaviour together with an elegant
mechanism to combine behaviour.  Novice users have little problems
typing `ls' to get a listing of the current directory.  Putting all
files modified after STAMP onto a tape is harder.%
 \footnote{{\tt tar cf /dev/rst0 `find .  -newer STAMP -type f -print`}}

This course only deals with the basic building blocks of the XPCE
environment.  In addition to the building blocks we will learn the
`glue' of XPCE: XPCE's executable objects that allow for elegant
connections between GUI components and the application.  Handling
the manual and debugging tools is another subject in this course.

Besides knowing the theory, practice and looking at examples are 
obligatory ingredients for learning a language.  


\section{Organisation of the PCE documentation}

Currently, the following documents are available for learning XPCE.  In
addition tothese documents, the demo programs, libraries and the sources
of the online manual may be examined as a source of examples.


\begin{itemize}
    \tick{Programming in PCE/Prolog} \cite{PCE:prolog}
Explains the basics of programming the PCE/Prolog environment.  It should
be the first document to read.
    \tick{PCE-4 Functional Overview \cite{PCE:overview}}
This document provides an overview of the functionality provided by PCE.
It may be used to find relevant PCE material to satisfy a particular
functionality in your program.
    \tick{PCE-4 User Defined Classes Manual \cite{PCE:udc}}
This document describes the definition of PCE classes from Prolog.
    \tick{PceDraw: An example of using PCE-4 \cite{PCE:draw}}
This document contains the annotated sources of the drawing tool PceDraw.
It illustrates the (graphical) functionality of PCE.  Useful as
a source of examples.
    \tick{The online PCE Reference Manual}
The paper documents are intended to provide an overview of the
functionality and architecture of PCE.  The online manual provides
detailed descriptions of classes, methods, etc.\ which may be accessed
from various viewpoints.
\end{itemize}