HLASM Language Reference

Terms, Literals, and Expressions
An ordinary symbol is not defined when:
It is used in the name field of an OPSYN or TITLE instruction. It can,
therefore, be used in the name field of any other statement in a source module.
It is used as the operand of a V-type address constant.
It is only used in the name field of a macro instruction and does not appear in
the name field of a macro-generated assembler statement. It can, therefore, be
used in the name field of any other statement in a source module.
It is only used in the name field of an ALIAS instruction and does not appear in
one of the following:
– The name field of a START, CSECT, RSECT, COM, or DXD instruction.
– The name field of a DSECT instruction and the nominal value of a Q-type
address constant.
– The operand of an ENTRY, EXTRN or WXTRN instruction.
Previously Defined Symbols: An ordinary symbol is previously defined if the
statement that defines it is processed before the statement in which the symbol
| appears in an operand.
An ordinary symbol must be defined by the time the END statement is reached,
however, it need not be previously defined when it is used as follows:
In operand expressions of certain instructions such as CNOP instructions and
some ORG instructions
In modifier expressions of DC, DS, and DXD instructions
In the first operand of an EQU instruction
In Q-type constants
When using the forward-reference capability of the assembler, avoid the following
types of errors:
Circular definition of symbols, such as:
X EQU Y
Y EQU X
Circular location-counter dependency, as in this example:
A DS (B-A)C
B LR 1,2
The first statement in this example cannot be resolved because the value of the
duplication factor is dependent on the location of B, which is, in turn, dependent
upon the length and duplication factor of A.
Literals may contain symbolic expressions in modifiers, but any ordinary symbols
used must have been previously defined.
Chapter 2. Coding and Structure 33