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Don't call it `Either`, call it `data Result e a = Ok a | Err e` (like in Elm and Rust), and call the transformer `ResultT`.

Do NOT do this. It's an anti-pattern: it assumes the side you bind on is an "okay" result and the other is an error, which is not always the case.

berdario

@berdari0

The opposite can also be seen as an antipattern: Result is a Functor, but Either shouldn't be (Result could be a newtype wrapper around Either, though). If needed a different newtype wrapper could have a left biased Functor instance as well

Really? Why wouldn't Either be a Functor?

Brendan Zabarauskas

@brendanzab

It could be two functors, it's just very unclear which. 'Right' was chosen due to silly mnemonic reasons for error handling. An hypothetical lang might allow you to bind either path with equal ease, but it would still be of use to have a type that is marked for passing errors.

There's no "silly mnemonics" involved at all, and no arbitrary choices. Left a because a is on the left in Either a b, Right b as it's on the right.

12:58 AM · Nov 22, 2017Twitter Web Client

Nov 22, 2017

So what happens when you need to write a function to find and print the errors? Now ok and error are flipped.

Replying to

and

That's definitely an issue. That's why I'd suggest having a wrapper with instances biased to the error. It's the less common case.

Replying to

and

Can't say I agree with wrappers. Pointless and tiresome.