[ribasushi]

A "maybe" type is logically incompatible with "subatomic I/O". When a sized-read() syscall results in a short read AND a raised error. The only sensible thing to do is to return both.

I am not familiar with Rust, but looking around the docs on Read [https://doc.rust-lang.org/std/io/trait.Read.html#errors] I see:

> If an error is returned then it must be guaranteed that no bytes were read.

Could someone elaborate how a system can satisfy this guarantee, seems impossible...?

[Measter]

That's an API choice. There's no technical reason at all why you couldn't return some kind of error AND read data if you wanted, you'd just have to make your Error type a product type.

[learc83]

That’s hardly a reason not to include a maybe type. In that particular case, instead of a maybe you can use a combination of sum and product types or just an additional ShortRead type.

NormalRead | ShortRead | Error

This case is also an example of why go’s idiom of using error value or return value doesn’t always work.

If you had a maybe type and a general sum type it would be clear when a function was going to return either or both.

[UK-Al05]

You could write sum type that handles multiple cases.

Value Error ValueAndError