I know it because (a) I read the article and (b) the combinators, brainfuck and so on have something magical to me: they show how unbelievably simple universal computation can be. When I was a kid I always imagined these layers underneath my code. BASIC, then the interpreter (written in assembly) then the machine code represenation of that read out by the CPU (in a way another interpreter, this time in hardware), and underneath that the logic gates. But there were so many logic gates, it still seemed quite complex. Adders, shifters, counters and so on.
What this does is it strips away that last layer and compresses it into the most simple abstractions. Just like the 'one instruction set computers', another favorite.
So did I. It was interesting, but didn’t really make me want to know more.
> the combinators, brainfuck and so on have something magical to me
Right, so in other words, it was because it’s interesting. Which is fine and something I said from from the start:
> Is It useful in any way? Is it just a curiosity? Does it develop your thinking? Any reason is fine (…)
I understand it can be interesting by itself (“Is it just a curiosity?”), I explicitly wanted to know if there’s something beyond that, which the article doesn’t say.
I think there is something beyond that, but possibly not for you.
Just like philosophy possibly isn't directly useful to you or men on the moon or a thousand other things that other people find fascinating, and useful to them.
What is useful to you is entirely yours, it is informed by your past and it is shaping your outlook of the future. So in that sense you could write that comment about anything that you find interesting but are not actually interested in, in the sense that you would pursue the thing for its own sake. It is probably better to approach such things in the same way that you would approach art: it may not be useful to you but if it is just interesting then that's enough.
The utility of a statue is very limited, though I guess technically you can hit someone over the head with a stone arm as a stand-in club. But that's not why statues are made. Sometimes the ability to wonder or observe is the utility and if you don't want to end up in a nihilistic place (nothing has ultimate utility on account of the heat death of the universe) then that may help you to appreciate the journey and the views rather than just the 'what's in it for me angle'.
For me the utility of these really low level computing abstractions lies in the fact that I have been wondering for a long time how I could compile a piece of software into a generic piece of hardware. These combinators are simple enough that they can be expressed with a gatecount that is low enough that I can make something more than just a counter (which I could do directly with fewer gates).
This is in turn related to cellular automata, computing fabrics and so on. If you aren't interested in any of those then there is zero utility here.
What this does is it strips away that last layer and compresses it into the most simple abstractions. Just like the 'one instruction set computers', another favorite.
https://esolangs.org/wiki/OISC
So the hardware all but evaporates, it is software until the very lowest level and then there is this very simple substrate.