Equality for Except

Stream: general

[Jonathan Reicher]

Is there a reason why the Except type doesn't have an instance for DecidableEq/BEq? It seems so trivial to me!

I just had to implement it myself for some code I am writing

[Robin Arnez]

Huh, well I guess Sum is an alternative

[Robin Arnez]

But the instance should probably exist

[Jonathan Reicher]

Right? I guess nobody needed it before :sweat_smile:
I would make a PR, but I'm not sure how to write the DecidableEq instance, and I have never done a PR before for an open source project

[Jonathan Reicher]

Unfotunently, of course, you can't use deriving for this because of the generic types

In general, if deriving delarations would work with generic types, like they do in rust it would be very convienent

[Aaron Liu]

Wait really?

[Jonathan Reicher]

Yeah I was shocked too, there is no instance
I tried the docs, tried inferInstance and tried loogle and no BEq and no DecidableEq

[Aaron Liu]

This works fine for me on the web server

deriving instance DecidableEq for Except

[Aaron Liu]

without any imports at all (except I guess import Init by default)

[Eric Wieser]

We should probably have the instance, but it's not obvious to me why you'd actually want to use it