I read this with pleasure, right up until the bit about the ants. Then I saw the note from myself at the end, which I had totally forgot writing seven years ago. I probably first encountered the article via HN back then as well. Thanks for publishing my thoughts!
Thanks! I'm glad to see I'm not the only one who went down this rabbit hole. :)
I considered parallelizing my solution as well, but the problem is that it only gives a linear speedup, while the problem space increases exponentially. I decided to focus on pruning the search tree instead, and that seemed to work pretty well (after much thinking).
As an F# developer with just enough category theory to follow along, I think this is really great.
I find the workaround for existential types in .NET particularly interesting, but it seems so verbose. Is there no way to do it with plain functions in order to avoid all the explicit type signatures?