Hello, I have a set of functions that validate som...

# arrow

[Oliver Eisenbarth]

Hello,
I have a set of functions that validate some object. I zip those to get a Validated and use them in an either block. Now I am wondering,
what the most idiomatic way to enabling 1-n of those functions via a configuration file would be.
In the end, I need to get from a list of Booleans (validationX enabled?) to a list of validation functions,
that need to get zipped for a result ...writing it in pseudocode...Either<InvalidFoo(reasons: Nel<Plausibility>>, ValidFoo>. Any ideas?

[simon.vergauwen]

1-n of those functions via a configuration file would be.

You mean generating Validated.zip for more than 9 parameters?
It's probably quite easy to write a little KScript that generates it, that is sadly the annoying thing about zip and n-arity functions like this in Kotlin.

There is however another way of composing zip to achieve higher arities that is quite simple.

validatedA.zip(
  validatedB,
  validatedC.zip(vaidatedD, ::Pair)
) { a, b, (c, d) -> ... }

By nesting zip2 inside another zip2 and using an intermediate Tuple you can compose 2x zip2 to achieve zip4.

Same is applicable for zip9 + zip9 to get arity-18.

[Oliver Eisenbarth]

Thank you for the good tip, but the arity is not a problem...at least atm. 🙂 🙌
What I am trying to achieve, is to write a function / or use one from Arrow if there is one,
that takes some Booleans from a config file - e.g. doValidateFoo: true, doValidateBar: true, doValidateBaz: false -
and zips only the corresponding functions:
If doValidateBar and doValidateBaz in the config file would be true, I want to run
validateBar().zip(validateBaz()) {ValidSomething(this)}.mapLeft{InvalidSomething(errors=it)} in the code.
I guess I need to fold a list of validateX functions, but I wanted to check if there's like an Arrow idiomatic way to do this.

[simon.vergauwen]

If you just need to run a bunch of validations in a list maybe you could do something like this, but I'm not sure how you're loading the data / functions.
If you have a List<() -> Validated<E, A>> than you can turn it into Validated<E, List<A>> by using traverse, an extension on Iterable.

Depending on how you load the booleans/functions from the config you could perhaps do something like.

val config: List<Pair<Boolean, () -> Validated<E, A>>> = ....

val validationsToRun: List<() -> Validated<E, A>> =
  config.mapNotNull { (boolean, function) -> function.takeIf { boolean } }

val result = validationsToRun.traverse { f -> f() }

[stojan]

Might wanna take a look at https://github.com/sksamuel/hoplite

[Oliver Eisenbarth]

Thank you @simon.vergauwen!
List<Pair<Boolean, () -> Validated<E,A>> and accumulating the functions to run seems perfect. I've defined validations as extensions on A but that doesn't matter. I will try where traversing the functions get's me, thanks a lot.

[Oliver Eisenbarth]

I am kinda stuck on this... 😨
Started with val config: List<Pair<Boolean, (Thing) -> ValidatedNel<E, Thing>>> and when I traverse those functions like in the example above, I get a List<Thing> where I would like to have a Thing. Zip does not work on lists of functions with arbitrary length...I must be missing something. 🤔
I also don't get why @simon.vergauwen chose validations functions to be () -> Validated<E,A>? Does that mean my approach with passing or extending from the thing to validate is wrong?

[simon.vergauwen]

Hey @Oliver Eisenbarth,
The reason for my types, and signatures is because I don't know a lot about your use-case. So that was based on a lot of assumptions. If you can share some snippets, or functions with signatures I could give you a more precise answer ☺️

[Oliver Eisenbarth]

Hi Simon, thanks for helping out. Unfortunately I can't copy paste code because of NDA, but I'll try to set up a personal project that shows the problem asap - who knows, maybe I can make a first blog article from it. 🙂
May I ping you again then or is that annoying? I really don't know how to behave here, please excuse. 😊

[simon.vergauwen]

No worries Oliver! ☺️ Yes, of course you can ping me. If you can share the function signatures, that would also be sufficient I think. You can replace any details with an unrelated domain.