Are there any common examples that show how to use...

# arrow

[kushalp]

Are there any common examples that show how to use Valid, Invalid and Either seamlessly? I'm thinking that this must be a fairly common pattern and would like to understand how others have done this in a simple way:

1. Make request to remote API that returns Either<ErrorException, ResponseData> where ResponseData is some data class
2. Validate all of the fields in ResponseData such that they can be converted into Invalid or Valid
3. Operate on the happy/sad paths

[stojan]

Maybe this helps https://arrow-kt.io/docs/0.10/patterns/error_handling/

[kushalp]

It's definitely a step in the right direction

[kushalp]

In my head it feels like it should be possible to do something like:

API call fails
1. Call external API using IO, returning Either<A, B>
2. API errors Left<A> so return a data class with all fields set to Invalid
API call successfully completes, validation fails
1. Call external API using IO, returning Either<A, B>
2. API succeeds with Right<B>, so validate all fields
3. Validation fails, so return a data class with all fields set to Invalid
4. This could be extended for partial validation, etc.
API completes, Validation completes
1. API returns Right<B>
2. Validation passes
3. data class is returned with all fields set to Valid

[kushalp]

And make that really clean

[kushalp]

Using IO, Either, and Validated together feels a bit clunky

[thanerian]

you could think that Validaded is a especialization of Either with extra utilities to accumulate error if you want to and other things.

you could go from IO<Either<A,B>> to IO<Validated<A,B>> back and forth without loosing information (they are Isomorph)

you don’t return data class with field set as invalid, you usually model with to branches, one correct and validated, and the other with error/or validation fails.

you usually return Valid<Model> or Invalid<ReasonError>