#chapter Primitive Data

This chapter describes the elementary datatypes of XPCE:

	constant	Constants (@nil, @default, ...)
	bool		@on, @off
	char_array	String of characters (superclass)
	name		Constant char_array (identifier)
	string		Editable char_array
	number		Integer value
	real		Floating point value
	date		Point in time

THE DATA TYPE INT

Besides these, XPCE offers data of type `int'.  Int is the only datum
not represented as a true object, mainly for efficiency and storage
reasons.  A PCE int is a 30 bits signed integer ranging from `@pce
<-min_integer' to `@pce <-max_integer' (-536870912 ..  536870911).

NOTE:	Many symbolic languages use more tag bits than PCE and thus
	?- get(@pce, min_integer, I) will not produce the required
	result.  get(real(@pce?min_integer), value, I) will on most
	systems return the requested value (be aware of rounding
	problems though).

When a message is sent to an `int' datum, PCE's message passing
mechanism will create a number object with the same value and 
invoke the method on this object.  Thus:

	?- send(3, larger, 2).

will succeed.  The following succeeds, but is a useless call (why?):

	?- send(3, plus, 2).
#end chapter

#class constant
#end class

#class bool
#end class

#class char_array
#description group content
The manipulation methods of this section are designed to return an
instance of the same class as the receiver of the method.  This is
wired in for the class name and class string.  For any other class,
<-modify is invoked on the receiver.  The argument is a char_array
object holding the text to be returned.  See <-modify for the
default definition.
#end description
#end class

#class name
#end class

#class string
#end class

#class number
#end class

#class real
#end class

#class date
#end class