Syntax
DEFINED symbol
The DEFINED operator returns a Boolean result which is true of the symbol is define at that point in the file, and false otherwise. Note that this operator only inquires whether the symbol is known to the assembler, not whether it has a known value: imported symbols are considered as defined even though the assembler does not know their value.
DEFINED cannot be used to detect whether a macro has been defined.
Example
The following show how defined works in a number of cases.
.IMPORT X Y EQU 10 B1 EQU DEFINED X ; true (1) B2 EQU DEFINED Y ; true (1) B3 EQU DEFINED Z ; false (0) not defined yet B4 EQU DEFINED U ; false (0) never defined Z EQU 100