HLASM Language Reference

Language Compatibility
Language Compatibility
The assembler language supported by High Level Assembler has functional
extensions to the languages supported by Assembler H Version 2 and DOS/VSE
Assembler. High Level Assembler uses the same language syntax, function,
operation, and structure as Assembler H Version 2. Similarly, the functions
provided by the Assembler H Version 2 macro facility are all provided by High Level
Assembler.
Migration from Assembler H Version 2 or DOS/VSE Assembler to High Level
Assembler requires an analysis of existing assembler language programs to ensure
that they do not contain:
Macro instructions with names that conflict with High Level Assembler symbolic
operation codes
SET symbols with names that conflict with the names of High Level Assembler
system variable symbols
Dependencies on the type attribute values of certain variable symbols or macro
instruction operands
With the exception of these possible conflicts, and with the appropriate High Level
Assembler option values, source language source programs written for Assembler
H Version 2 or DOS/VSE Assembler, that assemble without warning or error
diagnostic messages, should assemble correctly using High Level Assembler.
An E-Deck refers to a macro source book of type E that can be used as
the name of a macro definition to process in a macro instruction. E-Decks are
stored in edited format, and High Level Assembler requires that library macros be
stored in source statement format. A library input exit can be used to analyze a
macro definition, and, in the case of an E-Deck, call the VSE/ESA ESERV program
to change, the E-Deck definition, line by line, back into source format required by
the assembler, without modifying the original library file.
See the section titled Using the High Level Assembler Library Exit for Processing
E-Decks in the IBM VSE/ESA Guide to System Functions manual. This section
describes how to set up the exit and how to use it.
Assembler Language
The assembler language is the symbolic programming language that lies closest to
the machine language in form and content. You will, therefore, find the assembler
language useful when:
You need to control your program closely, down to the byte and even the bit
level.
You must write subroutines for functions that are not provided by other
symbolic programming languages, such as COBOL, FORTRAN, or PL/I.
The assembler language is made up of statements that represent either instructions
or comments. The instruction statements are the working part of the language and
are divided into the following three groups:
Machine instructions
Assembler instructions
4 HLASM V1R5 Language Reference