Is there a built in way of converting Option to a scalaz validation?

Question

I've been looking but I can't find an implicit converter. Obviously it would be trivial to write one but I'm wondering if I've missed one in the scalaz library somehow!

score 12 · Accepted Answer · answered Jan 19 '12 at 17:09

12

Scalaz has a implicit conversion of Option to OptionW, which declares the toFailure and toSuccess methods.

answered Jan 19 '12 at 17:09

Jean-Philippe Pellet

59,296
21
173
234

Any chance you could provide an example? I tried this with both scalaz._ and Scalaz._ imported, and I still get "error: value toValidationNel is not a member of Option" – Raymond Barlow Jul 09 '14 at 15:09
Doesn't OptionOps convert for you? – Toby Sep 29 '14 at 10:26
1

`toValidationNel` is a method usable on validation, not on option. – Daenyth Oct 03 '14 at 20:51
1

```import scalaz.syntax.std.option._; myOption.toSuccessNel(myError)``` – Tim Sep 16 '16 at 11:56

score 0 · Answer 2 · answered May 12 '19 at 12:57

Basically you have methods that transform "Some" into the "happy path" (in case of Validation -> Success, in case of Disjunction \/-) and then you need to define an error description for the None.

I use this when I receive an Optional parameter and I want to raise an error if is not provided.

Example:

scala> import scalaz.Scalaz._
import scalaz.Scalaz._

scala> import scalaz._
import scalaz._

scala> Some("clientId123").toSuccessNel("Client id is mandatory")
res0: scalaz.ValidationNel[String,String] = Success(clientId123)

scala> None.toSuccessNel("Client id is mandatory")
res1: scalaz.ValidationNel[String,Nothing] = Failure(NonEmpty[Client id is mandatory])

If you accumulate the errors using applicatives you can give a comprehensive error message to the final user, something like:

Client id is mandatory, country is mandatory, etc

Is there a built in way of converting Option to a scalaz validation?

2 Answers2