Definitely a fun alternative-history! It's a nice take to see `Option`s or `Result`s as a step towards logic programming. Typically once you introduce loops you need to have a way to combine `E`s; the way to represent an ordered set of things e.g. to be combined is to return a list of things, and then you're in logic programming world. [1]

[1]: https://wiki.haskell.org/Logic_programming_example

It's a bit weird to me that the result `not` discards the content of the value rather than just swapping its truthiness (not A?E : E?A).

> The closest thing I’ve seen is fallible expressions in Verse, but those are pretty different because they (i) don’t assign a value to an if without an else, and (ii) involve speculative execution.

Traditional ifs, and the ifs here, also involve speculative execution :) (i.e. execution that happens regardless of which branch you end up on). It's just delimited by the brackets of the if condition (a ‘failure context’ in Verseland). It's true that traditionally logic languages don't assign a value to failure. I guess algebraic effects (of which `Result` can be an example) can be seen as a generalization of failure in that way.

Amr Sabry &a. also have an interesting notion of ‘failure with value’ as the semantics of their negative types: https://dl.acm.org/doi/abs/10.1145/3434290 , http://lambda-the-ultimate.org/node/4964 (LtU for an older paper from the programme).