Added Result merge method

[brendanmaguire]

Also:

• is_ok and is_error use a comparison instead of a match as the comparison is faster
• Fixed a typo

[dbrattli]

Hi, thanks for the PR. Do you have any reference for the merge operator? Who else is using it? I would prefer operators like orElse and orElseWith, ref: https://demystifyfp.gitbook.io/fstoolkit-errorhandling/fstoolkit.errorhandling/result/orelsefunctions#result.orelsewith

[brendanmaguire]

Hi, thanks for the PR.

Happy to contribute 🙂

Do you have any reference for the merge operator? Who else is using it?

There is an Either#merge in Scala (docs). (Not sure of your familiarity with Scala but Either is pretty much the same as Result)

I would prefer operators like orElse and orElseWith, ref: https://demystifyfp.gitbook.io/fstoolkit-errorhandling/fstoolkit.errorhandling/result/orelsefunctions#result.orelsewith

merge is orthogonal to these imo. An example use of merge would be if you get a Result from your service layer and want to convert it to a HTTPResponse to return from the router layer.

Simple example:

def create(customer_id: str, email: str) -> HTTPResponse:
    service_result: Result[Customer, InvalidEmailAddress] = service.create_customer(customer_id, email)
    response: HTTPResponse = service_result.map(customer_to_response).map_error(invalid_email_to_response).merge()
    return response

I think the above code might also benefit from a Either#bimap (Scala cats docs) if you would be open to that addition? I tend to use bimap and merge together quite often in Scala.

Example (removing the extra variables from the above which I have included to highlight the types):

def create(customer_id: str, email: str) -> HTTPResponse:
    return (
        service.create_customer(customer_id, email)
        .bimap(customer_to_response, invalid_email_to_response)
        .merge()
    )

[brendanmaguire]

I've created a PR to add the or_else* methods too #226

[dbrattli]

Sorry I think I made a merge conflict with your PR. Anyways, I see that merge is the same as default_with(lambda x: x)

[dbrattli]

Nice, thanks for contributing this

[brendanmaguire]

Nice catch on the default_with. Pretty succinct now 🙂