What makes "FOCAL" FOCAL?

[mfleming]

(04-13-2020 09:29 PM)Orome Wrote:  Is there anything else that distinguishes the 41's programming semantics and features from those of earlier models? As near as I can tell, it's just a flavor of "keystroke programming", with some added usability features (mostly supplied by the alphanumeric capabilities) such as longer and more varied label names, textual display of operations (vs. key codes), etc. Anything else?

If you are looking for differences in the programming semantics (i.e. opcodes), then I would point to the soft END as a distinguishing feature of the HP41, compared to prior models. Early models treated program instruction space as a uniform array of keystroke steps (opcodes) that you could fill in. Later models added the GSB/RTN opcodes to modularly partition code, but it was still a uniform address space. For instance, the Voyager series (eg 15C) could have multiple programs in memory, each invoked by a GSB "label" keystroke. But you still had to think in terms of the 49 or 99 steps you had available to place code into, and where to place it.

Like a high level language, such as 71B BASIC, the 41 could support a structured programming approach to problem solving. You could decompose a program into separate functions, move functions between main memory, extended memory and external storage, and even collect them into function libraries (modules whose FAT served as linker global references). At this point you were starting to abstract the underlying hardware model and focus more on the problem to solve. I think that was an important step from just "what keys do I punch" to "how do I solve this problem."

Now, as to whether the 41 opcode set deserves its own name, you might as well ask why the Prime programming language is given the name PPL. Hey, why not