Either.chainLeft about fp-ts HOT 6 CLOSED

alt that gives access to the left value

@marcotoniut see orElse

from fp-ts.

Ah, sorry. I'm being stupid.

from fp-ts.

What I actually needed was the ability to chain a Validation. I see two ways of doing this:

• .fold
• convert validation to Either, perform chaining using .chain, and then convert back to a Validation.

const v = validation.failure<string, string>('foo')
v
  .fold(
    failure => validation.failure<string, string>(failure),
    success => validation.failure<string, string>(mapFn(success)),
  )

Does this sound like an anti pattern to you?

from fp-ts.

Here's what I ended up with:

export const chainValidation = <L, A, B>(
    leftSemigroup: semigroup.StaticSemigroup<L>,
    validationInstance: validation.Validation<L, A>,
    chainFn: (a: A) => validation.Validation<L, B>,
) => (
    validationInstance.fold(
        failure => validation.failure<L, B>(leftSemigroup, failure),
        chainFn,
    )
);

from fp-ts.

I arrived here actually seeking chainLeft, or a more robust alternative to Either, TaskEither and ReaderTaskEither's alt that gives access to the left value for the morphism. Is there a reason for why this shouldn't exist?

from fp-ts.

Well, that makes sense... Thank you.

from fp-ts.