[jammycakes]

> The unfortunately missing part of exceptions (in mainstream languages) is that they handle this invisibly. Figuring out, at compile time, what sort of exceptions can appear inside a given function is not obvious.

Figuring out, at compile time, what sort of exceptions appear inside a given function is a futile exercise in many contexts, and railway oriented programming does not fix it. Java tried this with checked exceptions and it fell out of favour because it became too unwieldy to manage properly.

In any significantly complex codebase, the number of possible failure modes can be significant, many of them are ones that you do not anticipate, and of those that you can anticipate, many of them are ones that you cannot meaningfully handle there and then on the spot. In these cases, the only thing that you can reasonably do is propagate the error condition up the call stack, performing any cleanup necessary on the way out.

"Handling this invisibly" is also known as "convention over configuration." In languages that use exceptions, everyone understands that this is what is going on and adjusts their assumptions accordingly.

[naasking]

> Java tried this with checked exceptions and it fell out of favour because it became too unwieldy to manage properly.

Because they did a half-assed job of it, and required the user to explicitly propagate error signatures. Inference and exception polymorphism are essential.

[Karunamon]

Checked exceptions always seemed to me to be an exercise of self-flagellation and enumerating badness; when most of the time there are a handful of specific errors that require special handling, with everything else logged/return error/possibly crash.

[layer8]

The problem is that the callee can’t decide for the caller which exceptions will require special handling. And for the caller to be able to make an informed decision about that, the possible exceptions need to be documented. Since this includes exceptions thrown from further down the call stack, checked exceptions are about the only practical way to ensure that all possible failure modes get documented, so that callers are able to properly take them into account in their program logic.