Example of scalaz' WriterT for Atlassian (pure functional logging)

WriterTExample.scala

import scalaz.WriterT
import scalaz.NonEmptyList
import scalaz.syntax.id._

import scalaz.std.option._
import scalaz.syntax.std.option._

type OptionLogger[A] = WriterT[Option, NonEmptyList[String], A]

val two: OptionLogger[Int] = WriterT.put(2.some)("The number two".wrapNel)
val hundred: OptionLogger[Int] = WriterT.put(100.some)("One hundred".wrapNel)

val twoHundred = for {
  a <- two
  b <- hundred
} yield a * b

println(twoHundred.value)
// Some(200)

twoHundred.written map { _.list } getOrElse List() foreach { println _ }

// The number two
// One hundred
//