either

Suppose I want to write a method with the following signature: def parse(input: List[(String, String)]): ValidationNel[Throwable, List[(Int, Int)]] For each pair of strings in the input, it needs to verify that both members can be parsed as integers and that the first is smaller than the second. It then needs to return the integers, accumulating any errors that turn up. First I'll define an error type: import scalaz._, Scalaz._ case class InvalidSizes(x: Int, y: Int) extends Exception( s"Error: $x is not smaller than $y!" ) Now I can implement my method as follows: def checkParses(p: (String,

I'm following the Scala course on Coursera. I've started to read the Scala book of Odersky as well. What I often hear is that it's not a good idea to throw exceptions in functional languages, because it breaks the control flow and we usually return an Either with the Failure or Success. It seems also that Scala 2.10 will provide the Try which goes in that direction. But in the book and the course, Martin Odersky doesn't seem to say (at least for now) that exceptions are bad, and he uses them a lot. I also noticed the methods assert / require... Finally I'm a bit confused because I'd like to

Option monad is a great expressive way to deal with something-or-nothing things in Scala. But what if one needs to log a message when "nothing" occurs? According to the Scala API documentation, The Either type is often used as an alternative to scala.Option where Left represents failure (by convention) and Right is akin to Some. However, I had no luck to find best practices using Either or good real-world examples involving Either for processing failures. Finally I've come up with the following code for my own project: def logs: Array[String] = { def props: Option[Map[String, Any]] =

I'm trying to validate the parameters of a method for nullity but i don't find the solution... Can someone tell me how to do? I'm trying something like this: def buildNormalCategory(user: User, parent: Category, name: String, description: String): Either[Error,Category] = { val errors: Option[String] = for { _ <- Option(user).toRight("User is mandatory for a normal category").right _ <- Option(parent).toRight("Parent category is mandatory for a normal category").right _ <- Option(name).toRight("Name is mandatory for a normal category").right errors : Option[String] <- Option(description)