Expression Substitution

Variables are dereferenced implicitly when used in the SETVAR, IF, WHILE, and CALC commands. Variables within an expression are also implicitly dereferenced. A variable can be implicitly dereferenced in any command, therefore, by including it in an expression.

The result of an expression, however, must be dereferenced explicitly. To do this, the expression is enclosed in brackets and preceded by an exclamation point. By explicitly dereferencing the expression and using implicit dereferencing of variables within the expression, the expression is more readable. The following examples demonstrate the use of explicit and implicit dereferencing when using expressions.

   :BUILD X;REC=![-2*40]



   :BUILD Y;DISC=![FINFO(FILE1,'EOF')*110]



   :ECHO ![UPS(FILE1)] does not exist.

Expressions are evaluated from left to right within the operator hierarchy. This sequence can be altered, however, by including parentheses in the expression. Parentheses can be nested to provide a specific sequence for evaluation.

The following example shows the expression that centers the variable TEXT on an 80-character line. Note that TEXT is implicitly dereferenced within the brackets and explicitly dereferenced outside the brackets.

   :ECHO ![RPT(" ",(80-LEN(TEXT))/2)]!string

In this example, a string is centered on an 80-character line by repeating the spacing character a number of times and concatenating the original string to it. Note the use of parentheses to override operator hierarchy and compute results in the proper sequence.