The summaries stress on describing what the class is commonly used 
for and what other classes are designed to cooperate with the class.
The classes are presented in alphabetical order. Some classes that 
are closely related and have symbol-names (>, +) are 
combined into one description, sometimes violating the alphabetical 
order.
- :=()
- 
Instances of this class are used to specify named arguments, see
section 2.4. Example:
...,
send(Editor, style,
     sensitive, style(underline := @on,
                      colour := dark_green)),
...,
- ==()
- 
- \==()
- 
Conditional code object that succeeds if both arguments evaluate to the 
same object. Normally used to specify the conditions of if 
or
while. The following 
example yields the names of all user-defined classes:
?- new(UDC, chain),
   send(@classes, for_all,
        if(@arg2?creator \== built_in,
           message(UDC, append, @arg1))).
- ?()
- 
Class ?, pronounced as 
`obtainer', represents a `dormant' get-operation. Obtainers are commonly 
used to `obtain' arguments for other code objects. For example:
...,
send(Dialog, append,
     new(TI, text_item(name))),
send(Dialog, append,
     button(ok, message(Dialog, return, TI?selection))),
- @=()
- 
Class @= assigns a symbolic 
reference name to the argument object. It is used to define global 
objects in the class-variable display.initialise. See the system 
defaults file
<pcehome>/Defaults. The following example 
fromDefaultscreates the objects @_dialog_bg 
and @_win_pen depending on whether 
or not the display is monochrome or colour.
display.initialise: \
        and(_dialog_bg @= when(@colour_display, \
                               grey80, white), \
            _win_pen   @= when(@colour_display, \
                               0, 1))
- and()
- 
Code object that executes its arguments one by one. It fails as soon as 
one of the arguments fails and succeeds otherwise. Commonly used to 
specify multiple actions for controllers. For example:
...,
get(Dialog, frame, Frame),
send(Dialog, append,
     new(Function, text_item(function))),
send(Dialog, append,
     button(switch_to,
            and(message(Frame, switch_to,
                        Function?selection),
                message(Function, clear)))),
...,
- application()
- 
An application object is a visual 
object used to combine multiple frames. 
See section 10.5 for a 
discussion on its usage.
- arc()
- 
Graphical primitive describing a section from a circle. It may be used 
to create a pie-chart segment.
?- new(A, arc(100, 20, 50)),
   send(A, close, pie_slice).
 
- area()
- 
Combination of X, Y, Width and Height 
used by
graphical to store 
the bounding box of the graphical. Also used to communicate with 
graphical objects and frames about their dimension.
...,
get(Box, area, area(X, Y, W, H)),
...,
 
- arrow()
- 
Arrow-head. Normally only used implicitly to attach arrows to a
line, arc 
or path, the subclasses 
of class
joint. See `joint->arrows'. arrow 
can be used directory to create fancy arrows.
?- new(L, line(0, 0, 100, 50, second))
 
- assign()
- 
Assign a value to an instance of class var, 
an XPCE variable. Used to realise variables in 
compound executable objects.
and(assign(new(C, var), @arg1?controller),
    message(C, ...),
    message(C, ...),
    ...)
- attribute()
- 
Attributes can be associated with any object to store data related to 
that object without the need to create a subclass. Normally attribute 
objects are used implicitly through the method
`object<->attribute'.
send(Frame, attribute, visualises, bicycle24)
 
- behaviour()
- 
Super class of method 
and variable, 
representing the two types of objects that can realise behaviour in 
classes. Not useful for the application programmer.
- bezier_curve()
- 
Create a Bezier curve from start to end using one 
or two control-points (quadradic or cubic Bezier curve). Bezier curves 
are nice smooth curves departing and arriving in a specified direction. 
See also path.
- binary_condition()
- 
- <()
- 
- =()
- 
- =<()
- 
- >()
- 
- >=()
- 
Arithmetic conditional code objects. These objects are normally used to 
specify the conditions of if 
or while. The following 
example creates a chain 
holding all graphicals on a device that either have <-width < 
5 or<-height < 5.
...,
get(Device?graphicals, find_all,
    or(@arg1?width < 5,
       @arg1?height < 5),
    SmallGraphicals),
...,
- binary_expression()
- 
- *()
- 
- +()
- 
- -()
- 
- /()
- 
Arithmetic functions, commonly used for computation of graphical 
dimensions or to specify spatial relations using class spatial 
or for simple functional computation from Prolog. For example:
...
send(Box, height, Text?height + 10),
...
 
- bitmap()
- 
A bitmap turns an image 
or pixmap into a 
graphical object that can be displayed on a device.
?- new(I, image('pce.bm')),
   new(B, bitmap(I)).
- block()
- 
A block is similar to and, 
but provides formal parameters.
?- send(block(new(A, var),
              new(B, var),
              message(@pce, write_ln, A, B)),
        forward, hello, world).
hello world
- bool()
- 
Class bool defines two 
instances: @on and @off, 
representing `true' and `false'. The use cannot create instances of this 
class.
...,
send(Image, transparent, @on)
...
 
- box()
- 
Graphical representing a rectangle. Corners can be rounded, the interior 
can be filled, the texture and thickness of the line can be controlled 
and a shadow can be defined.
?- new(B, box(100, 50)),
   send(B, radius, 10).
 
- browser()
- 
A browser is a window 
version of a list_browser. 
A browser visualises a list of dict_item 
objects. The items are organised in a dict, 
providing fast access to browser items, even if there are many items in 
the browser. Individual items may be coloured, underlined, etc. using 
the style mechanism also 
available for editor. 
Columns can be realised using tab_stops on the text_image 
object that displays the actual text of the browser.
?- new(B, browser),
   send_list(B, append, [gnu, gnat]).
 
- browser_select_gesture()
- 
Internal class dealing with selection handling in class
list_browser.
- button()
- 
A button is a push-button controller. It has an associated
message that is 
executed if the button is activated using the mouse. Inside a dialog, 
one button can be assigned as `default' button.
?- new(B, button(hello,
                 message(@pce, write_ln, hello))).
- c()
- 
Class c is a subclass of 
class host, providing 
communication to C and C++ code. It is not used directly by the 
application programmer.
- c_pointer()
- 
Class c_pointer 
encapsulates an anonymous C pointer (void *). It is used to 
register references to Prolog predicates with XPCE 
methods. See also chapter 7.
?- pce_predicate_reference(gnat:gnu(_,_), X).
X = @1190997/c_pointer
 
- chain()
- 
Class chain represents a 
single-linked list of arbitrary objects. Chains are commonly used inside XPCE 
to represent collections. Chains have methods to find elements, sort the 
chain, delete elements, etc. The predicate chain_list/2 
converts between an XPCE chain and a Prolog list. 
It also provides methods to run code on all elements of the list, which 
is generally faster than translating the chain to a Prolog list and 
using Prolog iteration. In the example, `device<-graphicals' 
returns a chain holding the graphicals displayed on the device. The 
example changes the font of all objects of class text 
to `bold'.
...,
send(Device?graphicals, for_all,
     if(message(@arg1, instance_of, text),
        message(@arg1, font, bold))),
...
- chain_hyper()
- 
Link two objects with a `chain'. If either dies, the other will die with 
it. See also the library library(hyper)and section 
10.11.
- chain_table()
- 
Version of a hash_table 
that allows multiple values to be associated with the same key. The key 
can be any object. If the value for a key is requested, a chain of 
values associated with this key is returned.
- char_array()
- 
Class char_array is 
a super-class of the classes string, 
representing modifiable text and name, 
representing read-only unique textual constants. Class char_array 
defines most of the analysis methods for its two subclasses. Almost the 
only usage of this class for application programmers is as type 
specifier for methods in user-defined classes that do not modify textual 
arguments.
insert_bold_text(Editor, Text:char_array) :->
        "Insert text with fragment of bold text"::
        get(Editor, caret, Start),
        send(Editor, insert, Text),
        get(Editor, caret, End),
        Len is End-Start,
        new(_, fragment(Editor, Start, Len, bold)).
- circle()
- 
Equivalent to an ellipse with the same <-width 
and<-height. Not used frequently.
- class()
- 
All XPCE classes are represented by an instance of 
class class. A class is 
a normal object and can thus be manipulated using
send/[2-12], get/[3-13] 
and new/2. 
Classes are normally only created and modified through the user-defined 
class layer described in
chapter 7. Get methods on classes are 
used to extract meta-information about its instances, as exploited by 
the online manual tools.
?- get(@pce, convert, box, class, ClassBox),
   get(ClassBox, super_class, X).
X = @graphical_class/class.
 
- class_variable()
- 
A class_variable 
provides can be used to describe class properties as well as to provide 
access to the XPCE
Defaultsdatabase. Typically, class-variables are defined 
similar to instance-variables in the XPCE/Prolog 
class definition:
 
:- pce_begin_class(title_text, text).
class_variable(font, font, huge, "Default font for titles").
...
 
- click_gesture()
- 
Class click_gesture 
is a recogniser 
that parses button-events to a click. If the click is detected, it will 
execute the associated message. This class is normally used to make 
graphical objects sensitive to clicks.
...,
send(Bitmap, recogniser,
     click_gesture(left, double, message(Bitmap, open))),
...
- code()
- 
Class code is a 
super-class for all `executable' objects. An important sub-class is 
class function, 
representing executable objects that yield a value. The method `code->forward: 
any ...' pushes the var 
objects @arg1, ... and then executes 
the code object. Code objects are often associated with controllers to 
describe the action the controller should perform. They also serve the 
role of lambda functions. See also section 
10.2.
?- send(message(@prolog, format, 'Hello ~w.', @arg1),
        forward, world).
Hello world.
- code_vector()
- 
A code_vector is a 
subclass of class vector 
that can represent functions as well as normal objects. It is used for 
packing multiple arguments passed to a variable-argument method. Do not 
use this class directly. See section 
7.5.2.
- colour()
- 
A colour represents an 
`RGB' triple.21Colour 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 
Colours are used as attributes to graphicals, windows, styles 
and
pixmaps
- colour_map()
- 
Manipulate the colourmap. Colourmaps are normally left untouched, but 
using a 256 entries colour palette in MS-Windows they can be used to 
improve full-colour image rendering. See also section 
10.10.1.
- connect_gesture()
- 
A connect_gesture 
allows the user to connect two graphicals by dragging from the first to 
the second. This requires two graphicals with handless 
attached, a link that is 
compatible with the handles and a connect_gesture 
associated width the graphical at which the connection should start. The 
demo program PceDraw as well as the XPCE Dialog 
Editor described in chapter A 
exploit connections and connect_gestures.
- connection()
- 
A connection is a 
line between two graphical objects that automatically updates on 
geometry, device and displayed-status changes to either of the connected 
graphicals. Both of the graphicals must have one or more handles 
associated with them. The connection can be attached to a specific 
handle, or to any handle of the proper
`handle<-kind'. 
In the latter case, the system will automatically choose the 
`best-looking' handle.
- constant()
- 
A constant is a 
unique handle. XPCE predefines the following 
constants: @nil, @default, 
and from the subclass bool, @on 
and @off. The use can define additional 
constants and give them their own unique meaning. The most obvious usage 
is to indicate a slot that can hold arbitrary data including @nil 
and @default is in a special state.
?- new(@uninitialised,
       constant(uninitialised,
                'Not yet initialised slot')).
- constraint()
- 
A constraint is a relation between 2 objects that has to be maintained 
if either of the objects is changed. The `constraint<-relation' 
is a description of the relation maintained by the constrained. The 
system defines the relations identity 
(both objects have an attribute that has same value) and spatial 
(general purpose geometry-relation between two (graphical) objects. It 
is possible to define new relation 
classes. Constraints are getting out of fashion as XPCE 
lacks a good mechanism to detect when an object has been changed and 
therefore evaluates the relation far too often. User-defined classes, 
possibly combined with hyper 
objects form an attractive alternative. The following keeps a text 
centered in a box.
...,
new(_, constraint(Box, Text, identity(center))),
...
 
- create()
- 
Function that creates an instance of a class. It is often required if a 
code fragment executed by an `iterator' method such as `chain->for_all' 
has to create objects. The following code generates dict_items 
from all send_methods 
of the specified class and displays them to a browser.
send_methods_of_class(ClassName) :-
        new(B, browser(ClassName)),
        get(@pce, convert, ClassName, class, Class),
        get(Class, send_methods, SendMethods),
        send(SendMethods, for_all,
             message(B, append,
                     create(dict_item,
                            @arg1?name,
                            @default,
                            @arg1))),
        send(B, open).
- cursor()
- 
A cursor defines the 
shape that indicates the position of the
pointer (also called mouse). 
The system provides a large set of predefined cursors from X11. 
The Win32 version adds the standard Windows cursors to this set. Cursors 
can also be created from an image. 
The demo program Cursors displays all defined cursors.
Cursors can be associated with graphicals and windows using the ->cursor 
method. They are also associated to gestures, 
where they define the cursor that is visible while the gesture is active 
(i.e. while the mouse-button that activated the gesture is down).
 Type-conversion converts names into cursor objects. Explicit creation 
of cursors is rarely used.
 
...,
send(Box, cursor, gobbler),
...
 
- date()
- 
A date objects represents 
a point in time. The underlying representation is the POSIX file 
time-stamp: seconds elapsed since 00.00, Jan 1-st, 1970. This limits the 
applicability of this class to time-stamps of computer resources 
(files), agenda systems and other domains that do not require a 
granularity below 1 second or have to represent time-stamps in far 
history or future. Class date 
can parse various textual representations into date objects.
?- send(@pce, format, 'It is now "%s"\n',
        new(date)?string).
It is now "Tue Jan 30 14:07:05 1996"
- device()
- 
A graphical device is a compound graphical. 
It is the super-class of class window. 
It is a sub-class of graphical, 
which implies devices can be used to create a consist-of structure of 
graphical objects, giving structure to a diagram. Devices are commonly 
refined to establish user-defined graphics, 
see section 10.12. See also 
class figure.
make_icon(Icon, Image, Label) :-
        new(Icon, device),
        send(Icon, display,
             new(BM, bitmap(Image))),
        send(Icon, display,
             new(T, text(Label, center))),
        send(T, y, BM?bottom_side),
        send(T, center_x, BM?center_x).
- dialog()
- 
A dialog is a window 
specialised for the layout and message handling required by dialog_items, 
the super-class of the XPCE controllers. 
In most cases, controller-windows are created by simply ->appending 
a number of controllers to a dialog window. The frame- 
and dialog-layout 
services take care of proper window sizes and layout of the controllers. 
Dialog windows are also involved in forwarding->report 
messages (see section 10.7) and 
keyboard accelerators, handling the default button.
:- pce_autoload(file_item, library(file_item)).
edit_file_dialog :-
        new(D, dialog('Edit File')),
        send(D, append,
             file_item(edit_file, '')),
        send(D, append,
             button(edit, message(@prolog, emacs, @arg1))),
        send(D, append,
             button(cancel, message(D, destroy))),
        send(D, open).
- dialog_group()
- 
A dialog_group is 
a collection of dialog_items. 
Dialog groups may be used to realise a (labeled) box around a group of 
controllers, or to combine multiple controllers into a compound one for 
technical or layout reasons. See also tab.
- dialog_item()
- 
Class dialog_item 
is a super-class of all XPCE controllers. It 
contains the code necessary to negotiate geometry with its neighbours 
and enclosing dialog 
window and provides default fonts for the label, etc. Class graphical 
defines similar methods to allow integration of raw graphical objects 
into dialog windows easily, but
graphical uses the 
more expensive object-level attributes for storing the necessary status. 
Open the class-hierarchy below class
dialog_item to 
find all available controllers.
- dict()
- 
A dict is an abbreviation 
of dictionary. Dicts map keywords to dict_item 
objects. Small dicts simply use a linear list (chain) 
of items. Large dicts will automatically built a
hash_table for 
quick lookup on the first request that profits from the availability of 
a table. A dict provides the storage for a
list_browser. See 
also class browser.
- dict_item()
- 
Item in a dict. The key 
is used for lookup. label is the text displayed by the browser 
(@default uses the key).
Object is an arbitrary object that can be associated to the 
dict. If a dict presents a set of XPCE objects, it 
is common practice to extract the key and or label from the object and 
store the object itself in the
`dict_item<->object' 
slot.A name is translated 
to a dict_item using the name as key, default label and @nil 
object. `dict_item<->style' 
can be used to give an item special attributes (colour, font, etc.).
 
- directory()
- 
A directory 
represents an node (folder) in the 
computer's file-system. Directories are most commonly used to enumerate 
the files and sub directories. Directory objects can also be used to 
create or delete directories from the file-system.
?- get(directory(.), files, Files).
 
- display()
- 
A display represents 
what X11 calls a screen, a desktop on which 
windows can be displayed with a mouse and keyboard attached to it.
XPCE support multiple display instances under X11 
and only the predefined default display @display 
under Win32. The display implements a number of global operations: 
getting the screen <-size, showing modal message 
boxes using->inform and->confirm, 
etc.
?- get(@display. size, size(W, H)).
W = 1024, H = 786
 
- display_manager()
- 
The object @display_manager 
is the only instance of this class. It represents the collection of 
available display 
objects and provides access to the system-wide event-dispatching 
services. It is the root of the consist-of hierarchy of visual 
objects as displayed by the Visual Hierarchy tool.
- edit_text_gesture()
- 
Used internally to handle selection inside a text 
object. See also the library library(pce_editable_text).
- editor()
- 
An editor is a 
general-purpose text editor. It is a graphical. Class view 
provides a window-based version of the editor. XPCE's 
editors have commands and key-bindings that are based on
GNU-Emacs. Editors are fully 
programmable. The associated
key_binding object 
parses key-strokes into commands that are defined as methods on the 
editor.
An editor is a compound object and a subclass of device. 
The other components are a text_image 
to form the actual display, a
text_buffer to 
provide the storage for the text, elementary operations on the text and undo, 
a text_cursor to 
indicate the location of the caret, and optionally a text_margin 
to visualise the presence of annotations.
 A single text_buffer 
can be associated with multiple
editor objects, 
providing shared editing.
 Editors can handle sensitive regions, different fonts, colours and 
attributes using fragment 
objects. All text windows in XPCE's demo programs 
(PceEmacs, cards from the online help, application help, etc.) either 
use class view or class editor to display the text. 
- elevation()
- 
An elevation object 
describes an elevated region on the screen. Elevations come in two 
flavours: as a shadow for monochrome displays and using light and dark 
edges on colour displays. The elevation object itself just contains the 
colour definitions. The actual painting is left to the graphical object 
the elevation is attached to.
Most controllers handle elevations. The only general purpose 
graphical supporting an elevation is figure. 
- ellipse()
- 
Elliptical shape. Class ellipse 
defines similar attributes as
box: pen, texture, 
fill_pattern and shadow. See also
circle.
- error()
- 
An error object 
represents a runtime message. Whenever an error is trapped or a message 
needs to be displayed, the system will invoke
`object->error: 
id, context ...' to the object that trapped the error. If this method is 
not redefined, the system will report the error using the `object->report' 
mechanism described in section 10.7. 
Errors can be prevented from being reported using pce_catch_error/2. 
The
Error Browser of the online manual shows all defined 
errors.The development system will report errors that are considered 
`programming errors' (undefined methods, type violations, invalid object 
references, etc.) to the terminal and start the tracer. See also
section 12. 
- event()
- 
An event represents an 
action from the application user: pressing a key, moving the mouse, 
pressing a mouse-button, or entering or leaving an area with the mouse. 
The main loop of XPCE will read window-system 
events from the computing environment (X11 or Win32). If the event 
concerns a repaint or similar system event, it will be handled 
appropriately. If it can be expressed as an XPCE 
event, an
event object will be 
created and send to the window for which the event was reported by the 
system using the method `event->post'.Graphical objects and windows can redefine their event handling using 
two mechanisms: by redefining the ->event method 
or by associating a recogniser 
object using `graphical->recogniser'.
 Normally, XPCE will read and dispatch events 
when `there is nothing else to do'. For processing events during 
computation, see `graphical
->synchronise' and `display->dispatch'.
 
- event_node()
- 
An event_node is a 
node in the event `is_a' hierarchy. See the demo program Events. 
Event-types are normally tested using
`event->is_a'.
event(Dev, Ev:event) :->
        "Forward all keyboard events to the text"::
        (   send(Ev, is_a, keyboard)
        ->  get(Dev, member, text, Text),
            send(Ev, post, Text)
        ;   send(Dev, send_super, event, Ev)
        ).
- event_tree()
- 
Event `is_a' hierarchy. The only instance is @event_tree.
- figure()
- 
A figure is a 
refinement of a device. 
It is a compound graphical, but in addition can define a background, 
surrounding box with margin, possibly rounded corners and elevation 
and a
clipping region. Finally, figures may be 
used not only to display all member graphicals, but also to show `one 
of' the member graphicals only. See `figure->status'. 
An example of the usage of figures are the `object cards' of the Inspector 
tool.
- file()
- 
An XPCE file 
object represents a file on the computers file-system. It can be used to 
specify a file, query a file for various attributes, read a file, etc. 
See also directory.
?- get(file('summary.doc', size, Size).
Size = 30762
- font()
- 
A font is a reusable 
object that describes the typeface of text.
Section 10.9 documents the 
specification of physical and logical fonts.
...,
send(Text, font, bold),
...
 
- format()
- 
A format describes the layout of graphicals 
on a
device. It can specify 
`tabular' and `paragraph' 
style layout. A format itself just specifies the parameters, `device
->format' actually realises the format.
- fragment()
- 
A fragment defines a 
region of text in a text_buffer 
using a start-position and a length. Fragments are automatically updated 
if the contents of the text_buffer changes. A fragment can be assigned a 
logical `category', called `style'. The editor 
visualising the text_buffer maps the style-names of fragments into
style objects using `editor->style'.
...,
send(Editor, style, title, style(font := huge)),
new(_, fragment(Editor, Start, Len, title)),
...
 
- frame()
- 
A frame is a collection 
of tiled 
windows. Frames handle the layout, resizing, etc. of its member windows. 
Any XPCE window is enclosed in a frame, though it 
is often not necessary to specify a frame explicitly. Applications are 
often implemented as subclasses of frame. Section 
10.6 describes the layout of windows inside a frame.
...,
new(F, frame('My application')),
send(F, append, new(B, browser)),
send(new(P, picture), right, B),
...
send(F, open).
- function()
- 
A function is a code 
object that yields a value when executed. See section 
10.2.2.
- gesture()
- 
Class gesture is the 
super-class for the recogniser 
classes that deal with the sequence mouse-button-down ... dragging ... 
mouse-button-up. This super-class validates the various conditions, 
handles the cursor and focus and activates the ->initiate,->drag and->terminate 
methods that are redefined in its subclasses. This class is often 
sub-classed.
- get_method()
- 
Specification of get-behaviour that is associated with a class using
`class->get_method' 
or with an individual object using `object->get_method'. Normally specified through the 
preprocessor layer defined in chapter 7.
- graphical()
- 
The most generic graphical object. This class defines generic geometry 
management, display, update, event-handling, etc. This class can be 
sub-classed to defined specialised graphics. See section 
10.12.
- grbox()
- 
Embed a graphical in a parbox. 
Using leftorrightalignment, grbox 
can also be used to have text floating around graphical illustrations. 
See section 11.10.
- handle()
- 
A handle defines a 
typed and named position on a graphical used by connections to connect 
to. The positions are formulas expressed in the with and height of the 
graphical. The following definitions are encountered regularly:
:- pce_global(@north_handle,
              new(handle(w/2, 0, link, north))).
:- pce_global(@south_handle,
              new(handle(w/2, h, link, south))).
:- pce_global(@east_handle,
              new(handle(0, h/2, link, east))).
:- pce_global(@west_handle,
              new(handle(w, h/2, link, west))).
- handler()
- 
A handler is the most 
primitive recogniser, 
mapping an event-type to a message. Since the introduction of the more 
specialised
gesture and key_binding 
as well as the possibility to refine the `graphical->event' 
method, it is now rarely used.
...,
send(Graphical, recogniser,
     handler(area_enter,
             message(Graphical, report,
                     'Hi, I''m %s',
                     Graphical?name))),
...
- handler_group()
- 
A handler_group 
is a compound recogniser 
object. When asked to handle an event, it will try each of its members 
until one accepts the event, after which it will return success to its 
caller. The following defines a combined move- an resize-gesture. Note 
the order: resize gestures only activate close by the edges of the 
graphical, while move gestures do not have such a limitation.
:- pce_global(@move_resize_gesture,
      new(handler_group(new(resize_gesture),
                        new(move_gesture)))).
- hash_table()
- 
A hash_table is a 
fast association table between pairs of objects. For example, @classes 
is a hash_table mapping class-names into class objects. Names are often 
used as keys, but the implementation poses no limit on the type 
of the key.
?- new(@ht, hash_table),
   send(@ht, append, gnu, image('gnu.img')).
?- get(@ht, member, gnu, Image).
- hbox()
- 
Superclass of tbox and grbox 
dealing with document-rendering. Instances of hbox 
itself can be used to define `rubber'. See section 
11.10 for details.
- host()
- 
Class host represents the host-language, 
Prolog for this manual. It predefines a single instance called @prolog. 
Sending messages to @prolog calls 
predicates. See also section 6.
?- send(@prolog, write, hello).
hello
 
- host_data()
- 
Support class for passing data of the host-language natively around in
XPCE. The Prolog interface defines the subclass
prolog_term and the interface-type prolog. 
Details are discussed in the interface definition in section 
6.2.
- hyper()
- 
A hyper is a binary relation 
between two objects. The relation can be created, destroyed and 
inspected. It is automatically destroyed if either of the two connected 
objects is destroyed. The destruction can be trapped. Messages may be 
forwarded easily to all related objects. See also section 
10.11.
- identity()
- 
An identity is a relation 
that maintains the identify between an attribute on one object and an 
attribute on another object. Given a slider and a box, the following 
ensures the selection of the slider is the same as the width of the box, 
regardless of which of the two is changed. See also constraint.
new(_, constraint(Slider, Box,
                  identity(selection, width)))
- if()
- 
Code object implementing a branch. All 
three arguments are statements. Both `then' and `else' are optional, and 
when omitted, simply succeed. Class if 
is most commonly used in combination with the iteration methods such as `chain->for_all':
...,
send(Device?graphicals, for_all,
     if(message(@arg1, instance_of, device),
        ...)),
...
- image()
- 
An image is a 
two-dimensional array of pixels. Images come in two flavours: 
monochrome, where each pixel represents a boolean and colour, where each 
pixel represents a colour. XPCE can save and load 
both monochrome and colour images. Images are displayed on a graphical 
device using a bitmap. 
They are also used to specify
cursor objects and the 
icon associated with a `frame'. See section 
10.10.
- int_item()
- 
Subclass of text_item 
for entering integer values. Has stepper buttons for incrementing and 
decrementing the value.
- joint()
- 
Class joint is a 
super-class of the various line-types with a start- end end-point. It 
provides the code dealing with attached
arrow-heads at 
either end. As well as common code to reason about the start and end. 
See also line, path,
arc and connection.
- key_binding()
- 
A key_binding 
object parses events into messages or methods on the object for which it 
is handling events. Key-bindings are used by the classes text, text_item, editor 
and
list_browser. 
They can be used to defined
keyboard-accelerators, though `menu_item<->accelerator' 
is generally more suitable for this purpose.
- label()
- 
A label is a controller 
used to display read-only text or
image. Labels can handle ->report 
messages. See section 10.7. The 
code below is the typical way to associate a label that will catch 
report messages for all windows of the frame 
in which the
dialog is enclosed.
...,
send(Dialog, append, label(reporter)),
...
 
- label_box()
- 
Subclass of dialog_group 
for the definition of compound controllers with a properly aligned label 
at their left-hand side.
- layout_manager()
- 
- layout_interface()
- 
A layout_manager 
may be attached to a graphical device 
(including a window) to 
manage the layout of graphicals displayed on the device, as well as 
painting the background of the device. See table 
for a typical example. 
- lbox()
- 
Class of the document-rendering system to render a list environment, a 
sequence of labels and text. See section 
11.10 for details.
- line()
- 
A line is a straight 
line-segment with optional arrows, thickness and texture. Class path 
implements a `multi-line'.
- link()
- 
A link is a reusable 
specification for a connection. 
Links are used for defining connections and connect_gesture 
objects. A connection knows about the link used to instantiate it. The 
example defines the handles, link 
and
connect_gesture 
and shapes that allows the user to create links with an error from `out' 
ports to `in' ports.
:- pce_global(@in_handle,
              new(handle(0, h/2, in, in))).
:- pce_global(@out_handle,
              new(handle(w, h/2, out, out))).
:- pce_global(@inout_link,
              new(link(out, in,
                       line(arrows := second)))).
:- pce_global(@link_in_out_gesture,
              new(connect_gesture(left, '',
                                  @inout_link))).
make_shape(S) :-
        new(S, box(50,50)),
        send_list(S, handle,
                  [@in_handle, @out_handle]),
        send(S, recogniser, @link_in_out_gesture).
- list_browser()
- 
A list_browser is 
a graphical version of a browser, 
the visualisation of a list of items (dict_item) 
stored in a
dict. The graphical 
version is sometimes displayed with other controllers on a dialog 
window. The example created a
list_browser 
holding all current Prolog source files. Double-clicking a file will 
start PceEmacs on the file. Selecting a file and 
pressing Consult will (re)consult the file.
show_source_files :-
        new(D, dialog('Prolog Source Files')),
        send(D, append, new(B, list_browser)),
        forall(source_file(X), send(B, append, X)),
        send(B, open_message,
             message(@prolog, emacs, @arg1?key)),
        send(D, append,
             button(consult,
                    message(@prolog, consult,
                            B?selection?key))),
        send(D, open).
- menu()
- 
Class menu realises 
various different styles of menus and is the super-class for popup. 
Basically, a menu presents multiple values, allows the user to choose 
one or more items (`menu
->multiple_selection') and defines a `look'. The `menu->kind' 
set the various attributes to often-used combinations. The other 
`look-and-feel' attributes may be used to fine-tune the result 
afterwards.Menu-items can have a textual or image 
label. Labels can be coloured and specify a different font.
 
...,
new(M, menu(gender, choice)),
send_list(M, append, [male, female]),
send(M, layout, horizontal),
...,
 
- menu_bar()
- 
A menu-bar is a row of pull-down menus. Many applications define a 
single menu-bar at the top of the frame presenting the various commands 
in the application.
:- pce_begin_class(my_application, frame).
initialise(F) :->
        send(F, send_super, initialise,
             'My Application'),
        send(F, append, new(MBD, dialog)),
        new(V, view),
        send(new(B, browser, left, V)),
        send(B, below, MBD),
        send(MBD, append, new(MB, menu_bar)),
        send(MB, append, new(F, popup(file))),
        send(MB, append, new(E, popup(edit))),
        send_list(F, append,
                  [ menu_item(load,
                              message(F, load)),
                    ...
- menu_item()
- 
Item of a menu or popup. 
For popup menus, the 
items are normally created explicitly as each item often defines a 
unique command. For menus, 
it is common practice to simply append the alternatives as menu_item 
will translate a
name into a menu_item 
with this <-value,<-message @default 
and a<-label created by `capitalising' the 
value.
- message()
- 
A message is a dormant 
`send-operation'. When executed using
->execute or->forward, a 
message is sent to the receiver. Message are the most popular code 
objects. See section 10.2 and 
many examples in this chapter.
- method()
- 
Class method is the 
super-class of send_method 
and
get_method. 
Instances of this class itself are useless.
- modifier()
- 
A modifier is a 
reusable object that defines a condition on the status of the three 
`modifier keys' shift, control 
and
meta/alt. Modifiers 
are used by class gesture 
and its sub-classes. They are normally specified through their 
conversion method, which translates a name 
consisting of the letters
s,candminto a modifier that 
requires the shift, control and/or meta-key to be down an the other 
modifier keys to be up. The example specifies a `shift-click' 
gesture.
...,
click_gesture(left, 's', single,
              message(...)),
...
- move_gesture()
- 
If a move_gesture 
is attached to a graphical, 
the graphical can be moved by dragging it using the specified 
mouse-button. See also move_outline_gesture.
...,
send(Box, gesture, new(move_gesture)),
...
 
- move_outline_gesture()
- 
Similar to a move_gesture, 
but while the gesture is active, it is not the graphical itself that is 
moved, but a dotted box indicating the outline of the graphical. If the 
button is released, the graphical is moved to the location of the 
outline. Should be used for complicated objects with many constraints or 
connections as a direct move_gesture would be too slow.
- name()
- 
A name is a unique 
textual constant, similar to an atom in 
Prolog. Whenever an atom is handed to XPCE, the 
interface will automatically create a name 
for it. There is no limit to the number of characters that can be stored 
in a name, but some Prolog implementations may limit the number of 
characters in an atom. On these platforms, it is 
implementation-dependent what will happen to long names that are handed 
to the Prolog interface.
- node()
- 
A node is a node in a tree 
of graphical 
objects.
...,
new(T, tree(new(Root, node(text(shapes))))),
send(Root, son, node(circle(50))),
send(Root, son, node(box(50, 50))),
...
 
- not()
- 
Code object that inverses the success/failure of its argument statement. 
Often used for code objects that represent conditions.
primitives(Device, Primitives) :-
        get(Device?graphicals, find_all,
            not(message(@arg1, instance_of, device)),
            Primitives).
- number()
- 
A number is the object 
version of an integer (int). If may be as a 
storage bin. To compute the widest graphical of a device:
widest_graphical(Device, Width) :-
        new(N, number(0)),
        send(Device, for_all,
             message(N, maximum, @arg1?width)),
        get(N, value, Width),
        send(N, done).
- object()
- 
Class object is the 
root of XPCE's class-inheritance hierarchy. It 
defines methods for general object-management, comparison, hypers, 
attributes, etc. It is possible to create instances of class
object, but generally 
not very useful.
- operator()
- 
Part of XPCE's object parser. Not (yet) available 
to the application programmer.
- or()
- 
Disjunctive code object. 
An or starts executing its argument statements left-to-right and 
terminates successfully as soon as one succeeds. The empty or 
fails immediately.
- parbox()
- 
Class to render text with mixed fonts and colours together with 
graphics. Class parbox 
is the heart of the document-rendering primitives described in section 
11.10.
- parser()
- 
Part of XPCE's object parser. Not (yet) available 
to the application programmer.
- path()
- 
A path is a multi-segment line. 
It comes in two flavours:
poly as a number of straight connected line-segments and
smooth as an interpolated 
line through a number of `control-points'. Its line attributes can be 
defined and the interior can be filled. Paths are used both to define 
new graphicals, for example a triangle, 
or to defines curves.
draw_sine :-
        send(new(Pict, picture), open),
        send(Pict, display, new(P, path)),
        (   between(0, 360, X),
                Y is sin((X * 6.283185)/360) * 100,
                send(P, append, point(X, Y)),
            fail
        ;   true
        ).
- pce()
- 
Class pce defines a single 
instance called @pce. Actions that 
cannot sensibly be related to a particular object are often defined on 
class pce.
?- get(@pce, user, User).
User = jan
 
- pen()
- 
Reserved for future usage.
- picture()
- 
A picture is a window 
with scrollbars, normally used for application graphics. If a graphical 
window without scrollbars is required, window 
should be considered.
- pixmap()
- 
A pixmap is a subclass 
of image that is 
reserved for colour images. All functionality of this class is in class
image. The main reason 
for its existence is that some graphical operations require a 
colour image and the introduction of a class for it is the only way to 
allow this to be specified using XPCE's type 
system. The ->initialise method is specialised 
for handling colour images.
- point()
- 
Position in a two-dimensional plane. Together with size 
and
area used to communicate 
with graphicals about geometry.
...
get(Box, center, Point),
get(Point, mirror, Mirrored),
send(Box, center, Mirrored),
...
 
- popup()
- 
A popup menu is a menu 
that is shown after pressing a button on the object the menu is attached 
to. Popups are used in two different contexts, as pulldown 
menus attached to a menu_bar 
and as popup-menus associated with windows or individual graphical 
objects.
Popups are ->appended to menu_bars. Various 
classes define the method->popup to associate popup menus. Finally, class popup_gesture 
provides a gesture that operates popup menus.
 A popup consists of menu_items, 
each of which normally defines a message to be executed if the 
corresponding item is activated. Pull-right sub-menus are realised by 
appending a popup to a popup.
 
...,
new(P, popup(options)),
send(P, append,
     new(L, popup(layout, message(Tree, layout, @arg1)))),
send_list(L, append, [horizontal, vertical, list]),
send(P, append,
     menu_item(quit, message(Tree, destroy))),
...
- popup_gesture()
- 
A popup_gesture 
parses events and activates a popup 
menu. Popup gestures are explicitly addressed by the application 
programmer to define compound gestures involving a popup:
:- pce_global(@graph_node_gesture,
              make_graph_node_gesture).
make_graph_node_gesture(G) :-
        new(P, popup),
        send_list(P, append, [...]),
        new(G, handler_group(connect_gesture(...),
                             move_gesture(middle),
                             popup_gesture(P))).
- process()
- 
A process encapsulates 
a stream- or terminal program to get its input from a graphical program 
and redirect its output to the same graphical program. Various of the XPCE 
tools and demo programs exploit processes: The M-x shell, M-x 
grep and other shell commands of PceEmacs, the ispell 
program and the chess front-end. See also socket.
- progn()
- 
Code object with semantics like the LISP progn function. A progn 
executes its statements. If all statements are successfully executed and 
the last argument is a function, 
execute the function and return the result of it or, if the last 
argument is not a function, simply return it. Used infrequently in the XPCE/Prolog 
context.
- program_object()
- 
The super-class of almost the entire `meta-word' of XPCE: classes, 
behaviour, attributes, types, etc. Class program_object 
defines the XPCE tracer. See tracepce/1 
and breakpce/1.
- quote_function()
- 
Most of XPCE is defined to evaluate function 
objects at the appropriate time without the user having to worry about 
this. Sometimes however, type-checking or execution of a statement will 
enforce the execution of a function where this is not desired. In this 
case class
quote_function 
can help. As a direct sub-class of
object, it will 
generally be passed unchanged, but type-conversion will translate 
extract the function itself if appropriate, while delegation allows the 
quote_function to be treated as a function.
In the example, ChainOfChains is a chain holding chains as 
its elements. The task is to sort each of the member chains, using the
function ?(@arg1, 
compare, @arg2) for sorting. If 
not enclosed in a quote_function, 
the message will try to evaluate the function. Now it passes the 
quote_function unchanged. The `chain->sort' 
method requires a code 
argument and therefore the function will be extracted from the 
quote_function.
 
...,
send(ChainOfChains, for_all,
     message(@arg1, sort,
         quote_function(?(@arg1, compare, @arg2)))),
...
- real()
- 
A real is XPCE's 
notion of a floating-point number. Reals are represented using a C 
single-precision `float'. Reals define the 
same operation as class number, 
its integer equivalent.
- recogniser()
- 
Class recogniser is 
the super-class of all event-parsing classes. The sub-tree gesture 
handles mouse-button related events, key_binding 
handles typing and handler 
may be used for all events. The main purpose of this class itself is to 
provide a type for all its sub-classes.
- regex()
- 
A regex is XPCE's 
encapsulation of the (GNU) Regular Expression 
library. Regular expression form a powerful mechanism for the analysis 
of text. Class regex can 
be used to search both char_array 
(name and string) 
text and text from a text_buffer 
as used by editor. It 
is possible to access the `registers' of the regular expression.
?- new(S, string('Hello World')),
   new(R, regex('Hello\s +\(\w+\)')),
   send(R, match, S),
   get(R, register_value, S, 1, name, W).
W = 'World'
- region()
- 
A region defines a 
sub-region of a graphical. They are used to restrict handler 
objects to a sub-area of a graphical. Backward compatibility only.
- relation()
- 
Class relation is the 
super-class of identity 
and
spatial. Relations 
form the reusable part of
constraints. Class relation 
may be sub-classed to define new relation-types.
- resize_gesture()
- 
A resize_gesture 
handles mouse-drag events to resize a graphical object on the corners or 
edges. See also move_gesture 
and
resize_outline_gesture.
...,
send(Box, recogniser, new(resize_gesture)),
...
 
- resize_outline_gesture()
- 
Outline version of the resize_gesture, 
often used to resize objects that are expensive to resize, such as editor 
or
list_browser.
- resize_table_slice_gesture()
- 
Gesture that can be used together with class table 
to allow the user dragging the boundaries between columns and rows in a 
table. See also section 11.5.
- resource()
- 
A resource is data 
associated with the application. It is most commonly used to get access 
to image-data. Example:
 
resource(splash, image, image('splash.gif')).
show_splash_screen :-
        new(W, window),
        send(W, kind, popup),           % don't show border
        new(I, image(resource(splash))),
        get(I, size, size(W, H)),
        send(W, size, size(W, H)),
        send(W, display, bitmap(I)),
        send(W, open_centered),
        send(timer(2), delay),
        send(W, destroy).
        
- rubber()
- 
Defines how elastic objects in the document-rendering system such as
hbox and its subclasses 
are. Used by parbox to 
realise layout. See section 11.10 
for a full description of the rendering primitives.
- scroll_bar()
- 
A scroll_bar is 
used to indicate and control the visible part of a large object viewed 
through a window. Though possible, scroll_bars are rarely used outside 
the context of the predefined scrollbars associated with list_browser, editor 
and window.
...,
send(Window, scrollbars, vertical),
...
 
- send_method()
- 
A send_method maps 
the name of a method selector onto an implementation and 
defines various attributes of the method, such as the required 
arguments, the source-location, etc. Send-methods are normally specified 
through user-defined classes preprocessor as described in chapter 
7.
- sheet()
- 
A sheet is a dynamic set 
of attribute/value pairs. The introduction of object-level attributes 
implemented by `object
<->attribute' and user-defined classes have 
made sheets obsolete.
- size()
- 
Combination of <-width and<-height 
used to communicate with graphical objects about dimension. See also point 
and area.
- slider()
- 
Controller for a numeric value inside a range that does not require 
exact values. Specifying volume or speed are good examples of the use of 
sliders. They can also be used to realise a percent-done 
gauge.
...,
new(Done, slider(done, 0, 100, 0)),
send(Done, show_label, @off),
send(Done, show_value, @off),
...
send(Done, selection, N),
send(Done, synchronise),
...
 
- socket()
- 
Communication end-point for a TCP/IP or 
Unix-domain interprocess communication stream. XPCE 
supports both `server' and `client' sockets. On the Win32 platform, only 
TCP/IP sockets are provided and only Windows-NT supports server sockets. 
The library(pce_server)provides a good starting point for 
defining server sockets. The support executable xpce-client 
may be used to communicate with XPCE server 
sockets. See also PceEmacs server mode as defined inlibrary('emacs/server').
- source_location()
- 
Specifies the location in a source file. Used by method 
objects to register the location they are defined.
- source_sink()
- 
Abstract super-class of file, resource 
and
text_buffer for 
type-checking purposes. All source_sink 
objects may be used for storing and retrieving image-data. Notably a resource 
can be used for creating images (see
section 9 and text_buffer 
can be used to communicate images over network connections (see section 
11.9).
- spatial()
- 
A spatial defines a 
geometry relation 
between two objects. The first two equations express the reference 
point of the 1st graphical in terms of its x, y, w and h. The second 
pair does the same for the second graphical, while the remaining two 
equations relate the mutual widths and heights. The example defines the 
second graphical to be 10 pixels wider and higher than the first, to 
share the same lower edge and be centered horizontally.
new(_, constraint(Gr1, Gr2,
                  spatial(xref=x+w/2, yref=y+h,
                          xref=x+w/w, yref=y+h,
                          w2=w+2, h2=h+2)))
- stream()
- 
Class stream is the 
super-class of socket 
and
process, defining the 
stream-communication. It handles both synchronous and asynchronous input 
from the socket or process. It is not possible to created instances of 
this class.
- string()
- 
A string represents a 
string of characters that may be modified. This class defines a large 
number of methods to analyse the text that are inherited from char_array 
and a large number of methods to manipulate the text. Class regex 
can analyse and modify string objects. There is no limit to the number 
of characters in a string. Storage is (re)allocated dynamically and 
always is `just enough' to hold the text. For large texts that need many 
manipulations, consider the usage of text_buffer 
that implement more efficient manipulation.
Strings are commonly used to hold descriptions, text entered by the 
user, etc. 
- style()
- 
A style defines 
attributes for a text fragment 
as handled by a editor/classtext_buffer 
or a dict_item as 
handled by a list_browser/dict. 
It defines the font, fore- and background colours as well as 
underlining, etc. The example defines a browser that displays files 
using normal and directories using bold font.
make_browser(B) :-
        new(B, browser),
        send(B, style, file, style(font := normal)),
        send(B, style, directory, style(font := bold)),
        send(B, open).
append_file(B, Name) :-
        send(B, append,
             dict_item(Name, style := file)).
append_dir(B, Name) :-
        send(B, append,
             dict_item(Name, style := directory)).
- syntax_table()
- 
Syntax tables are used by class text_buffer 
to describe the syntax of the text. They describe the various 
syntactical categories of characters (word-characters, 
digit-characters), the syntax for quoted text, for comments as well as a 
definition for the end of a sentence and paragraph. Syntax tables are 
introduced to support the implementation of modes 
in PceEmacs. See also the
emacs_begin_mode/5 
directive as defined in library(emacs_extend).
- tab()
- 
A tab is a subclass of dialog_group, 
rendering as a collection of dialog_items 
with a `tag' associated. Tabs are normally displayed on a tab_stack, 
which in turn is displayed on a dialog. 
Skeleton:
        new(D, dialog(settings)),
        send(D, append, new(TS, tab_stack)),
        send(TS, append, new(G, tab(global))),
        send(TS, append, new(U, tab(user))),
        ...,
        <fill G and U>
        ...,
        send(D, append, button(ok)),
        send(D, append, button(cancel)).
- tab_stack()
- 
Defines a stack of tagged sub-dialogs (tab 
objects) that can be displayed on a dialog. 
See tab for an example.
- table()
- 
A table defines a 
two-dimensional tabular layout of graphical objects on a graphical device. 
The functionality of XPCE tables is modelled after 
HTML-3. Example:
simple_table :-
        new(P, picture),
        send(P, layout_manager, new(T, table)),
        send(T, border, 1),
        send(T, frame, box),
        send(T, append, text('row1/col1')),
        send(T, append, text('row1/col2')),
        send(T, next_row),
        send(T, append,
             new(C, table_cell(text(spanned, font := bold)))),
        send(C, col_span, 2),
        send(C, halign, center),
        send(P, open).
- table_cell()
- 
Provides the layout_interface 
to a table. Table cells 
are automatically created if a graphical is appended to a table. 
Explicit creation can be used to manipulate spanning, background and 
other parameters of the cell. 
- table_column()
- 
- table_row()
- 
- table_slice()
- 
These classes are used for storing row- and column information in
table objects. They are 
normally created implicitly by the table. References to these objects 
can be used to change attributes or delete rows or columns from the 
table. Example:
 
        ...,
        get(Table, column, 2, @on, Column),
        send(Column, halign, center),
        ...
- tbox()
- 
Add text using a defined style 
to a parbox. Part of 
the document-rendering infra-structure. See section 
11.10.
- relation_table()
- 
A relation_table 
defines a multi-column table data object that can have one or more 
indexed key fields. They are (infrequently) used for storing 
complex relational data as XPCE objects.
- text()
- 
Graphical representing a string in a specified font. Class text defines 
various multi-line and wrapping/scrolling options. It also implements 
methods for editing. Class editable_text as defined in library(pce_editable_text)exploits these methods to arrive at a flexible editable text object.
- text_buffer()
- 
A text_buffer 
provides the storage for an editor. 
Multiple editors may be attached to the same text_buffer, 
realising shared editing on the same text. A text_buffer has an 
associated syntax_table 
that describes the character categories and other properties of the text 
contained. It can have fragment 
objects associated that describe the properties of regions in the text.
See class editor for 
an overview of the other objects involved in editing text. 
- text_cursor()
- 
Cursor as displayed by an editor. 
Not intended for public usage. The example hides the caret from an 
editor.
...,
send(Editor?text_cursor, displayed, @off),
...
 
- text_image()
- 
A text_image object 
is used by the classes editor 
and
list_browser to 
actually display the text. It defines the tab-stops 
and line-wrapping properties. It also 
provides methods to translate coordinates into character indices and 
vise-versa. The user sometimes associates recogniser 
objects with the text_image 
to redefine event-processing.
- text_item()
- 
A text_item is a 
controller for entering one-line textual values. Text items (text-entry-field) 
can have an associated
type and/or value-set. 
If a value-set is present or can be extracted from the type using `type<-value_set', 
the item will perform completion, which 
is by default bound to the space-bar. If a type is specified, the typed 
value will be converted to the type and an error will be raised if this 
fails. The following text-item is suitable for entering integers:
...,
new(T, text_item(height, 0)),
send(T, type, int),
send(T, length, 8),
...
 
- text_margin()
- 
A text_margin can 
be associated with an editor 
using
`editor->margin_width' > 
0. If the text_buffer 
defines fragments, and the style 
objects define `style<-icon', 
the margin will show an icon near the start of the fragment. After the 
introduction of multiple fonts, attributes and colour this mechanism has 
become obsolete.
- tile()
- 
Tiles are used to realise the `tile-layout' of windows in a
frame. Section 
10.6 explains this in detail. Tiles can also be used to realise 
tabular layout of other re-sizable graphical objects.
- tile_adjuster()
- 
Small window displayed on top of a frame 
at the right/bottom of a user-adjustable window. Dragging this window 
allows the user the adjust the subwindow layout.
- timer()
- 
Timers are used to initiate messages at regular intervals, schedule a 
single message in the future or delay execution for a specified time. 
The example realises a blinking 
graphical. Note that prior to destruction of the graphical, the timer 
must be destroyed to avoid it sending messages to a non-existing object.
...,
new(T, timer(0.5, message(Gr, inverted,
                          Gr?inverted?negate))),
...
- tokeniser()
- 
A tokeniser returns 
tokens from the input source according to the syntax specified. It is 
part of the XPCE object parser and its 
specification is not (yet) public.
- tree()
- 
Trees realise hierarchical layout for graphical 
objects. Class
tree itself is a subclass 
of figure. The 
hierarchy is built from node 
objects, each of which encapsulates a graphical. Trees trap changes to 
the geometry of the displayed graphicals and will automatically update 
the layout. For an example, see node.
- tuple()
- 
Anonymous tuple of two objects. Commonly used by get-methods that have 
to return two values.
- type()
- 
A type defines, 
implicitly or explicitly, a set of object that satisfy the type, as well 
as optional conversion rules to translate certain other object to an 
object that satisfies the type. The basic set consists of a type for 
each class, defining the set of all instances of the class or any of its 
sub-classes, a few `primitive' types (int, char and event_id are 
examples). Disjunctive types can be created. See also
section 3.2.1 and section 
7.5.1.
?- get(type(int), check, '42', X). X = 42
 
- var()
- 
A var object is a function 
that yields the stored value when evaluated. Vars in XPCE 
have global existence (like any object), but local, dynamically scoped, 
binding. Scopes are started/ended with the execution of (user-defined) 
methods, `code->forward' 
and the execution of a block.The system predefines a number of var 
objects providing context for messages, methods, etc: @arg1, 
... @arg10 for argument forwarding,
@event for the current event, @receiver 
for the receiver of an event or message and @class 
for the class under construction are the most popular ones. Class block 
and and give examples of 
using these objects. 
- variable()
- 
A variable is a 
class' instance-variable. They are, like
send_method and get_method, 
normally defined through the user-defined classes preprocessor described 
in chapter 7.
- vector()
- 
Vector of arbitrary objects. Vectors can be dynamically expanded by 
adding objects at arbitrary indices. Vectors are used at various places 
of XPCE's programming world: specifying the types 
of methods, the instance variables of a class, to pack the arguments for 
variable-argument methods, etc. They share a lot of behaviour with
chain can sometimes be 
an attractive alternative.
- view()
- 
A view is a window 
displaying an editor. 
View itself implements a reasonable powerful set of built-in commands 
conforming the GNU-Emacs key-bindings. See also PceEmacs 
and
show_key_bindings/1.
- visual()
- 
Visual is the super-class of anything in XPCE that 
can `visualise' things. The class itself defines no storage. Each 
subclass must implement the `visual<-contains' 
and `visual<-contained_in' 
methods that define the visual consists-of hierarchy as shown by the
Visual Hierarchy. Class visual itself plays a role in 
the->report mechanism as described in section 
10.7 and defines
`visual->destroy' 
to ensure destruction of a sub-tree of the visual consists-of hierarchy.
- when()
- 
Class when realises a 
function version of if. It 
evaluates the condition and then returns the return-value of 
either of the two functions. It is commonly used to define conditional 
class-variable values.
editor.selection_style: \
        when(@colour_display, \
             style(background := yellow), \
             style(highlight := @on))
- while()
- 
Code statement executing body as long as condition 
executes successfully. Not used frequently. Most iteration in XPCE 
uses the
->for_all,->for_some,<-find 
and<-find_all methods defines on most collection 
classes.
- window()
- 
The most generic XPCE window class. A window 
is a sub-class of
device and thus capable 
of displaying graphical objects. One or more windows are normally 
combined in a frame as 
described in section 10.6. 
The four main specialisations of window are dialog 
for windows holding controllers, view 
for windows holding text, browser 
for windows displaying a list of items and finally, picture 
for displaying graphics.
Class window can be 
used as a graphics window if no scrollbars are needed. 
- window_decorator()
- 
A window_decorator 
is a window that displays another window and its `decorations': 
scrollbars and label. A picture 
for example is actually a window displayed on a window-decorator 
displaying the scrollbars. Almost never used directly by the application 
programmer.