Collapse OS -- Why Forth?
Teckla writes:
It appears the leadership of Collapse OS have decided to switch from Z-80 to Forth. In this article, they explain their reasoning.
Collapse OS' first incarnation was written in Z80 assembler. One of the first feedbacks I had after it went viral was "why not Forth?". I briefly looked at it and it didn't seem such a great choice at first, so I first dismissed it. Then, I had what alcoholics refer to as a "Moment of clarity".
[...] The Z80 asm version of Collapse OS self-hosts on a RC2014 with a 5K shell on ROM, a 5K assembler binary loaded in RAM from SD card (but that could be in ROM, that's why I count it as ROM in my project's feature highlights) and 8K of RAM. That is, it can assemble itself from source within those resources.
[...] If I wanted to re-implement that assembler feature-for-feature in Forth, it would probably require much more resources to build. Even though higher level words are more compact, the base of the pyramid to get there couldn't compete with the straight assembler version. This was under this reasoning that I first dismissed Forth.
So, again, what makes Forth more compact than assembler? Simplicity. The particularity of Forth is that it begins "walking by itself", that is, implementing its own words from its base set, very, very early. This means that only a tiny part of it needs to be assembled into native code. This tiny part of native code requires much less tooling, and thus an assembler with much less features. This assembler requires less RAM.
What is more compact than something that doesn't exist? Even Z80 assembler can't beat the void.
That's how although Forth is not more compact that native code (duh!), a Forth Collapse OS achieves self-hosting with as much resources than its Z80 counterpart.
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