Meanwhile, apparently the Rust folks can't make up their minds, so they support lots of different functional styles of error handling.
In other words, there is no way to abstract over the case analysis in Go. It sounds like you're saying this is a good thing. I think it's bad.
> ... apparently the Rust folks can't make up their minds
Wow, I'd say the opposite. In Go, the only thing all `error` objects have in common is the `Error()` method, which returns a description. If you want to investigate the causal chain of an error (to achieve what stack-traces give you in languages with exceptions), there is no standard way, even for errors in the standard library. Some errors are basically just strings, others are structs with other fields that you can access by using runtime type assertions.
Rust, on the other hand, has the `Error` trait, which includes a `cause` method, returning the underlying error if one exists. This alone seems to me like an improvement in consistency over Go.
But I don't think abstracting over case analysis is a good idea when it hurts readability. The combinator stuff looks like it's adding layers of shortcut notations that obscure the control flow.
(It also abstracts over case analysis, among other things, but it's only one very simple form of case analysis, so the mental overhead is low. Combinators on the other hand abstract over many different types of case analysis, so the mental burden can be high, especially if you aren't already comfortable using them.)
The API signature is always the same regardless of how the caller handles errors: a function returning Result. The differences are never exposed in APIs (arguably even less than in Go, since you can't recover from a panic in Rust except at thread boundaries).
> Meanwhile, apparently the Rust folks can't make up their minds, so they support lots of different functional styles of error handling.
They all boil down to the same thing. There's no inability to make up our minds with error handling any more than supporting both for-loops and map represents inability to make up our minds. Nobody dings Python for supporting list comprehensions in addition to for loops. Sometimes functional programming is short and sweet, and you should be able to use it; other times, for loops are better. and_then() is just the functional syntax to "try!"'s imperative syntax.
It seems like having lots of trivial error combinators is less like Python's list comprehensions and more like what came before it. I'll point out that Guido has had second thoughts about lambda, reduce(), filter() and map(), though in the end he only dropped reduce. [1].