Scalaz Introduction

Motivation

I’ve been using Scalaz for a while now and I remember not having any guides that provide a gentle introduction. It was a lot of scouring around, reading source code, and watching tech talks that gave me the understanding that I have now. This series of posts is intended at filling that gap by providing simple, step-by-step tutorials that will help you get productive quickly without compromising on the functional programming concepts.

What is Scalaz?

The documentation for Scalaz (pronounced Scala-zee or Scala-zed) states:

Scalaz is a Scala library for functional programming.
It provides purely functional data structures to complement those from the Scala standard library. It defines a set of foundational type classes (e.g. Functor, Monad) and corresponding instances for a large number of data structures.

In a nutshell, Scalaz aims to do three things:

  • Provide new datatypes that are not present in the core Scala library
  • Provide new operations on existing types a.k.a. pimp the library
  • Provide general-purpose functions so that you don't have to re-write them

    • I’ll provide a quick example of each of these without going into any details.

    New Datatypes

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    scala> import scalaz._
    import scalaz._

    scala> import Scalaz._
    import Scalaz._

    scala> NonEmptyList.nels(1, 2, 3)
    res0: scalaz.NonEmptyList[Int] = NonEmpty[1,2,3]

    Here we are creating a NonEmptyList which is a list that is guaranteed to have atleast one element i.e. it’s never empty.

    New Operations on Existing Types

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    scala> import scalaz._
    import scalaz._

    scala> import Scalaz._
    import Scalaz._

    scala> val o = Option(3)
    o: Option[Int] = Some(3)

    // Scalaz way
    scala> o some { _ + 1 } none { 0 }
    res0: Int = 4

    // Scala way
    scala> o.fold(0)( _ + 1 )
    res1: Int = 4

    The first way of extracting value from an Option comes from Scalaz and is much more expressive compared to using fold from Scala standard library.

    General-Purpose Functions

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    scala> import scalaz._
    import scalaz._

    scala> import Scalaz._
    import Scalaz._

    scala> List(1, 2, 3) |+| List(4, 5, 6)
    res0: List[Int] = List(1, 2, 3, 4, 5, 6)

    The |+| operator from Scalaz conveniently concatenated the two Lists together.