Use the new Result type instead of Choice for Errors

[gusty]

We'll need to adjust to what would be the new standard for signaling errors.

The question is what do we do with the existing type Choice<'OK,'Error>.

I think we should keep if as much as possible for backwards compatibility, but not just between this library version, there might be a lot of source code that uses the Choice convention and needs to keep working without doing a big refactoring.

[wallymathieu]

Indeed.

• You could add a Compatibility namespace with Choice<'Ok,'Error>
• You could add a Next namespace with Result<,>
• Or go the YoLo path and have both in the same namespace (there might be some things that need to be fixed first though)

[gusty]

Or go the YoLo path and have both in the same namespace (there might be some things that need to be fixed first though)

I decided to use this approach when possible, ie for Functors, Applicatives and Monads. But there are other situations where only one should be the default to model computations.

See my comment on the commit for a summary of all these changes.

I'm happy to discuss further, or eventually re-open this issue and revert that commit.

[wallymathieu]

No, I think selecting one approach is good.