Post by Polansoft

When most people think of assembler, they imagine big sheet of code and a maze of jumps through this code that only the original programmer can decipher months later. But IBM High Level Assembler (HLASM) has a capability that changes the picture entirely: macros. The very same algorithm can be written in two very different styles: ◼️ Traditional assembler ▪️ Explicit labels (LOOP, SKIP, DECR) ▪️ Conditional branches (BL, BNL, BNH) ▪️ Manual subroutine setup and teardown ▪️ Control flow reconstructed mentally from branch targets ◼️ Macro-based HLASM ▪️ DO WHILE / ENDDO ▪️ IF / ENDIF ▪️ SUBIN / SUBOUT ▪️ Structured, readable flow that resembles a high-level language What's interesting is that these aren't two different languages. HLASM's macro facility expands structured constructs into the same assembler instructions during assembly. The resulting object code is effectively identical. That means: ✅ No runtime overhead ✅ Full access to low-level instructions when needed ✅ Ability to create reusable abstractions tailored to your environment There's also a maintainability benefit. Structured macros can eliminate entire classes of mistakes related to label management and control-flow logic. In some cases, they can even prevent subtle bugs that are easy to introduce in hand-written branch-and-label code. This is one of the reasons assembler on the mainframe often surprises people who haven't worked with it before. HLASM isn't just "raw assembly", it ranges from machine-level programming to highly structured, readable code. It doesn't provide the same level of abstraction as high-level programming languages, but it is a great compromise between code readability and efficiency. And that's one of the reasons why not every HLASM code needs to be re-written. So the next time someone says "assembler is unreadable", show them both versions: same language and machine code, but completely different developer experience. #HLASM #Assembler #ProgrammingLanguages #LegacyModernization #ProductDevelopment #SoftwareEngineering #EnterpriseSoftware #Mainframe #MainframeModernization #LegacySystems #zOS