How to combine two Validation<Error, Unit>?

[davidyu2023]

I am not sure if I am heading the right direction. If both are Success, then combining the two would return Success. Otherwise return Fail with all Errors from both. How do I do this?

[louthy]

Use the 'coalescing' operator:

    Validation<Error, Unit> mx = ...;
    Validation<Error, Unit> my = ...;

    var mr = mx | my;

I kinda wish I'd used the & operator, but there it is.

You can also use Apply (which is the applicative-functor operator), it allows you to get at the values of the validation if they all succeed, and returns all the errors if any fail.

   var mr = (mx, my).Apply((x, y) => unit);

Finally, if you only care about getting the first error and not all errors:

    var mr = from x in mx
             from y in my
             select unit;

Definitely finally, there's a nice ValidateCreditCard example in the unit-tests that visits all the different approaches to using the Validation type, it's worth a look.

[davidyu2023]

Thanks a lot @louthy!

[louthy]

No problem @davidyu2023 and thanks for the donation, it's very much appreciated :-)

[BrunoJuchli]

@louthy
Is there also something like an Apply function to be applied to an IEnumerable<Validation<FAIL,SUCCESS>> instead of a tuple?
So that in the end I get something like Validation<FAIL,SEQ<SUCCESS>>?
Well actually, I would convert the SEQ<SUCCESS> to another type R, but whether I do that inside the Apply or with a followup Map doesn't matter that much to me.

Thank you

[harrhp]

validations.Sequence().Map(f)