Which is more idiomatic: Option<Result<T>> or Result<Option<T>>?

[juleskers]

I'm having a bit of a deja vu This might be interesting related reading:

Is there something more idiomatic than Option<Result<T, string>>?

Hello, I'm working on a parser and I'm scanning the input string using a (peekable) iterator. I have a function that consumes items from the iterator and should return three different things: a token if it manages to parse one an error message when something goes wrong something that tells me that I reached the end of the iteration on the input string. I have a working example using Option<Result<Token, string>>. It works fine but it doesn't feel very idiomatic. What do you think about it? …

The difference is in the nesting, and thus also which part of the operation the Err applies to.
I tried to write some more examples, but they all end up being basically what Vitaly already wrote...

The difference is indeed quite subtle, and I think there are some cases where Result<Option<>> is better, and other cases where Option<Result<>> is better.