How APPX Uses T/F Status Indicators
As a part of the ILF (Integrated Language Facility), APPX incorporates a unique condition testing facility that allows you to perform complex logic checking operations. As the basis of this facility, the system maintains a set of five internal true/false status indicators. These indicators provide you with a method to control the logic flow within an ILF routine, depending on the result of conditions encountered at runtime.
ILF statements (except for those with keywords *, **, and LABEL) incorporate within their syntax the ability to enter values for comparison against the current status of the internal true/false status indicators. The first five positions of most statements are reserved for this purpose; hence, these five positions are known as true/false execution conditions. From left to right, they correspond to the five true/false status indicators, levels 1 through 5, respectively. Based on the result of the comparison between the execution conditions and the internal status indicators, APPX either executes or bypasses a statement.
For example, the following is an example of a SET statement used to modify the value of the field WORK ALREADY POSTED:
As coded, this statement would only be executed if the current status of the five internal indicators is TTFTF, to agree with the execution condition values specified in the statement.
By the same token, several statements set the values of the true/false status indicators. As each of these statements operates, if it finds a true or met condition, it sets the value of the next true/false status indicator to T. If the statement encounters a false or unmet condition, it sets the next indicator to F. For example, consider the following statement:
If the IF statement determines that the value of the field named COUNT is 6, the first true/false status indicator is set to T. If the value of the field is not equal to 6, the indicator is set to F.
Both the true/false status indicators and the true/false execution conditions will be discussed more completely further in this chapter.