Add error accumulating function to RefType

[fthomas]

Add a function to RefType that is similar to refine but instead of returning an Either it should return a type that can accumulate errors (something like cats.Validated). bond has this as can be seen here: https://github.com/fthomas/refined/blob/v0.8.2/modules/docs/feature_comparison_bond.md#what-bond-has-but-refined-not

[fthomas]

https://meta.plasm.us/posts/2015/12/17/error-accumulating-decoders-in-circe/ might be interesting here.

[ysusuk]

hi @fthomas, i'll be glad to work on this issue) can you give me some hints on where to start?

[fthomas]

That would be great @ysusuk. The easiest way right now to accumulate errors is by using cats' toValidatedNel enhancement for the Either. That way we can write something like this:

(refineV[Positive](x).toValidatedNel |@| refineV[NonEmpty](y).toValidatedNel).map2 {
  (x1, y1) => ???
}

with nice error accumulation. I think my idea was to have a variant of refineV that returns directly a ValidatedNel[String, F[T, P]] instead of an Either[String, F[T, P]]. The easiest way to accomplish this is to copy refineV to the cats module and replace Either with ValidatedNel. If it would have a better name than refineV, that would be nice too. :-)

[ysusuk]

hi @fthomas
do you mean as well to create another RefinePartiallyApplie in cats package, that will return ValidatedNel instead of Either?

[fthomas]

@ysusuk Yes. :-)

[ysusuk]

@fthomas can you pls assign this issue on me)

[fthomas]

It seems that I only can assign it to myself.

[fthomas]

I'm closing this in favor of #382.