The same day Cloudflare had its unwrap fiasco, I found a bug in my code because of a slice that in certain cases went past the end of a vector. Switched it to use iterators and will definitely be more careful with slices and array indexes in the future.
Was it a fiasco? Really? The rust unwrap call is the equivalent to C code like this:
int result = foo(…);
assert(result >= 0);
You can write buggy code in rust just like you can in any other language.
You might think that the Haskell behavior is “safer” in some sense, but there’s a huge gotcha: exceptions in pure code are the mortal enemy of lazy evaluation. Lazy evaluation means that an exception can occur after the catch block that surrounded the code in question has exited, so the exception isn’t guaranteed to get caught.
Exceptions can be ok in a monad like IO, which is what they’re intended for - the monad enforces an evaluation order. But if you use a partial function like fromJust in pure code, you have to be very careful about forcing evaluation if you want to be able to catch the exception it might generate. That’s antithetical to the goal of using exceptions - now you have to write to code carefully to make sure exceptions are catchable.
The bottom line is that for reliable code, you need to avoid fromJust and friends in Haskell as much you do in Rust.
The solution in both languages is to use a linter to warn about the use of partial functions: HLint for Haskell, Clippy for Rust. If Cloudflare had done that - and paid attention to the warning! - they would have caught that unwrap error of theirs at linting time. This is basically a learning curve issue.