Evolving the OCaml Programming Language (2025) [pdf]

For people using OCaml, there’s one thing that kinda discourages me in it, that is exceptions as part of the API in the standard library.

Because exceptions aren’t checked, this effectively means that a language designed for type safety has as much type safety as python, because it’s very easy to forget handling something, and get runtime errors.

How do you deal with this day to day? I assume it’s impossible to just believe that all the code you pull in doesn’t use exceptions?

> as much type safety as python

There's no type unsafety from unchecked exceptions, because uncaught exceptions are not unsound. Even Haskell has them (error and undefined), because from a theoretical standpoint they're equivalent to reaching an infinite loop. (Now, recovering from an exception isn't unsound either, but it might mess with your usual mutable invariants.)

In more practical terms, concerning overall correctness, OCaml has been adding option-returning variants of those functions, so most exceptions raised from the stdlib nowadays are much more likely to be intended by the author.

I don't think Haskell is a good language to model our idea of error handling off of. It's one of many bugbears I have with that language, that it uses the Maybe monad as an error type. It technically works, but doesn't provide a meaningful distinction between "This function might not return anything, and this is defined behavior" and "This function has a singularity". MonadError exists, but I can't think of anywhere it shows up without digging deep into dragon caves of the compiler. Everything a normal user is going to touch will deal exclusively in Maybes.

I'm not a fan of Rust as a language for many reasons, but I will give it credit for making proper usage of the Result monad. They could have abused Option the same way Haskell abuses Maybe, but they didn't.