That's interesting. Having learned Haskell long before Rust (and having been programming in C++ for a long time) I found Rust's ?-notation to be annoyingly limited due to the reasons you gave, and also annoying syntactically. I saw in many Rust sources it's often tucked away at the end of lines, flush against the last character, a single character which changes the meaning of the line, well, the whole function, but is often lost to me visually, and I have to scan the line to see it. But I guess people got used to it or just don't bother parsing all characters in a line of code like I do.
When you say "They’re still trying to get the migration done today... " you mean Rust's core developers, right? Is there anywhere I can read up on it?
Ah no the migration I was referring to is `Applicative`: I just upgraded our "primary" Nix `devShell` to use `9.2.4` (`RecordDotSyntax` is finally here, may the thousand-year reign of the Glorious Glasgow Haskell Compiler commence! /s) and it's hitting me with deprecation notices about `return = ...` rather than `return = pure` and/or omitting and explicit `return`. Which makes sense, the rationale is at https://gitlab.haskell.org/ghc/ghc/-/wikis/proposal/monad-of....
I remember when I was working on `Haxl` at FB in like, 2015 or 2016, it needed `ApplicativeDo` and that was like, quite the novelty in industrial Haskell (I think it was already a no-brainer to the research/OSS/etc. crowd). So mainstreaming `Applicative` into the effects hierarchy has been going on for 6 or 7 years that I know about, and I bet a lot longer than that (the paper introducing `Applicative` is from 2008: https://www.staff.city.ac.uk/~ross/papers/Applicative.html).
At the risk of inviting an old-fashioned HN brigade gang-tackle: I think it indirectly illustrates why Rust is going to end up going all-in and ditching the ?-notation. Please don't hurt me.
When you say "They’re still trying to get the migration done today... " you mean Rust's core developers, right? Is there anywhere I can read up on it?