You also want an ePaper? Increase the reach of your titles
YUMPU automatically turns print PDFs into web optimized ePapers that Google loves.
62 CHAPTER 3. LANGUAGE<br />
The control types are only used within the generic <strong>HDevelop</strong> type tuple. A tuple of length 1<br />
is interpreted as an atomic value. A tuple may consist of several numerical data items with<br />
different types. The standard representation of a tuple is a listing of its elements included into<br />
brackets (see figure 3.1).<br />
Tuple constant<br />
Value<br />
Value<br />
string<br />
integer<br />
Value<br />
[ ]<br />
real<br />
,<br />
boolean<br />
Figure 3.1: The syntax of tuple constants.<br />
℄ specifies the empty tuple. A tuple with just one element is to be considered as a special case,<br />
because it can either be specified in the tuple notation or as an atomic value: ℄ defines the<br />
same constant as . Examples for tuples are:<br />
℄<br />
½½<br />
¼º½<br />
³ÌÜس<br />
½℄<br />
½¼¼º¼¸½¼¼º¼¸¾¼¼º¼¸¾¼¼º¼℄<br />
³ÐÆѳ¸³ÜØÒ×ÓÒ³℄<br />
½½¸¼º½¸³ÀÙÓ³℄<br />
The maximum length of a tuple is limited to 1000000.<br />
3.3 Variables<br />
Names of variables are built up as usual by composing letters, digits and the underscore ³ ³.<br />
The maximum length of a variable name is limited to 256 characters. The kind of a variable<br />
(iconic or control variable) depends on its position in the parameter list in which the variable<br />
identifier is used for the first time (see also chapter 3.1). The kind of the variable is determined<br />
during the input of the operator parameters: whenever a new identifier appears, a new variable<br />
with the same identifier is created. Control and iconic variables must have different names.<br />
The value of a variable (iconic or control) is undefined until the first assignment defines it (the<br />
variable hasn’t been instantiated yet). A read access to an undefined variable leads to a runtime<br />
error (ÎÖÐ Ü ÒÓØ Ò×ØÒØØ).<br />
Instantiated variables contain tuples of values. Depending on the kind of the variable the data<br />
items are either iconic objects or control data. The length of the tuple is determined dynamically<br />
by the performed operation. A variable can get new values any number of times, but once a value<br />
has been assigned the variable will always keep beeing instantiated, unless you select the menu<br />
<strong>HDevelop</strong> / 2000-11-16