ISEQ instruction

The ISEQ instruction forces the assembler to check if the statements in a source module are in sequential order. In the ISEQ instruction, you specify the columns between which the assembler is to check for sequence numbers.


>>-+-----------------+--ISEQ--+------------+-------------------><
   '-sequence_symbol-'        '-left,right-'

sequence_symbol: Is a sequence symbol.
left: Specifies the first column of the field to be sequence-checked. If specified, left must be a decimal self-defining term with value 1 - 80.
right: Specifies the rightmost column of the field to be sequence checked. If specified, right must be a decimal self-defining term with value 1 - 80, and must be greater than or equal to left.

If left and right are omitted, sequence checking is ended. Sequence checking can be restarted with another ISEQ statement. An ISEQ statement that is used to end sequence checking is itself sequence-checked.

The assembler begins sequence checking with the first statement line following the ISEQ instruction. The assembler also checks continuation lines.

Sequence numbers on adjacent statements or lines are compared according to the 8 bit internal EBCDIC collating sequence. When the sequence number on one line is not greater than the sequence number on the preceding line, a sequence error is flagged, and a warning message is issued, but the assembly is not ended.

If the sequence field in the preceding line is spaces, the assembler uses the last preceding line with a non-space sequence field to make its comparison.

The assembler checks only those statements that are specified in the coding of a source module. This includes any COPY instruction statement or macro instruction. The assembler does not check:

Statements inserted by a COPY instruction
Statements generated from model statements inside macro definitions or from model statements in open code (statement generation is discussed in detail in How to specify macro definitions)
Statements in library macro definitions