Watch the video of me presenting this at Scala Exchange 2014 : https://skillsmatter.com/skillscasts/5835-bootstrapping-a-scala-mindset The aim of this session was to map out the key stages involved in moving productively from a Java to a Scala mindset. As Scala gains increasing traction in OO developer communities, more and more Java developers are in the progress of making the move from being Imperative-comfortable to FP-fluent. Many are lured by the terser syntax, others by the promise of powerful high-level constructs, and more still by the thrill of challenging themselves and learning something almost entirely new to them. The problem however, is that for many their initial enthusiasm soon wears off and the realization of how much a mind-shift this really is sinks in. In this session I discussed in some detail the key steps along a path which via much trial-and-error, has proved for me to be effective in undertaking this transition. We began at the base-camp of understanding (Java-concepts to let go of, the initially-unfamiliar syntax, the equally-unfamiliar maths idiom) and from there up into the lower foothills (the basics of the type system, infix notation, ""everything is an expression"" and referential transparency) before progressing on to the lower peaks of the language (Pattern-matching with case classes and partial functions) and ending at one significant Monadic taster (Option, map/flatMap and the for-comprehension). For maximum benefit I also pointed out the pain points I encountered, techniques and resources I used to overcome these, and we ended by mentioning next steps and further inroads into the language.

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17. val v = Vector(1, 2, 3, 4)
v.foreach( print("> " + n) )
// from: Atomic Scala v1.1

18. def show(n: Int): Unit = {
print("> " + n)
}
val v = Vector(1, 2, 3, 4)
v.foreach(show)
// from: Atomic Scala v1.1

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20. // Everything is an expression
// including "statements"
if(1 > 0) {
"It's true!“
} else {
"It’s false!"
}
// adapted from: Atomic Scala v1.1

21. // Everything is an expression
// including "statements"
val result =
if(1 > 0) {
"It's true!"
} else {
"It's false!"
}
println(result) // “It’s true!”
// adapted from: Atomic Scala v1.1

22. // Everything is an expression,
// including “blocks“
val calc =
{
val i1 = 2
val j1 = 4/i1
i1 * j1
}
println(calc)
// from: Atomic Scala v1.1

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24. // Infix Notation means that
// this...
a.method(b)
// ... can be written like this...
a method b
// from: Atomic Scala v1.1

25. // And Infix Notation also means
// that this...
a.method()
// ... can be written like this...
a method
// from: Atomic Scala v1.1

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27. class Simple(val s:String) {
def getA() = s
val getB = s + "ya"
}
val simple = new Simple("Hi")
// from: Atomic Scala v1.1

28. class Simple(val s:String) {
def getA() = s
val getB = s + "ya"
}
val simple = new Simple("Hi")
simple.getA() // res0: String = Hi
// from: Atomic Scala v1.1

29. class Simple(val s:String) {
def getA() = s
val getB = s + "ya"
}
val simple = new Simple("Hi")
simple getA // res4: String = Hi
// from: Atomic Scala v1.1

30. class Simple(val s:String) {
def getA() = s
val getB = s + "ya"
}
val simple = new Simple("Hi")
simple getB // res5: String = Hiya
// from: Atomic Scala v1.1

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34. def inc: (i:Int) = i + 1
// this is a TOTAL function
// from: "Programming in Scala
// (2nd Ed.)", pp 332-333

35. def inc (i:Int) = i + 1
// this is a TOTAL function
def fraction (d:Int) = 42 / d
// this is a PARTIAL function
// It is not defined for d == 0
// E.g. It’ll throw an exception
// if called with 0
// from: "Programming in Scala
// (2nd Ed.)", pp 332-333

36. import scala.collection.immutable._
val second: List[Int] => Int = {
case x :: y :: _ => y
}
// from: "Programming in Scala
// (2nd Ed.)", pp 332-333

37. import scala.collection.immutable._
val second:
PartialFunction[List[Int],Int] = {
case x :: y :: _ => y
}
// from: "Programming in Scala
// (2nd Ed.)", pp 332-333

38. import scala.collection.immutable._
val second:
PartialFunction[List[Int],Int] = {
case x :: y :: _ => y
}
second.isDefinedAt(List(5,6,7))
res30: Boolean = true
// from: "Programming in Scala
// (2nd Ed.)", pp 332-333

39. import scala.collection.immutable._
val second:
PartialFunction[List[Int],Int] = {
case x :: y :: _ => y
}
second.isDefinedAt(List())
res30: Boolean = false
// from: "Programming in Scala
// (2nd Ed.)", pp 332-333

40. class Problem(val msg:String)
extends Exception
def test(n:Int) =
try {
f(n)
} catch {
case err:Problem
=> s"Failed: ${err.msg}"
}
// from: Atomic Scala v1.1

41. class Problem(val msg:String)
extends Exception
def test(n:Int) =
try {
f(n)
} catch {
case err:Problem => s“whoops“
case err:Disaster => s“BOOM!“
}
// from: Atomic Scala v1.1

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43. case class Cat (name:String,
age:Int)
// from: Atomic Scala v1.1

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45. def acceptAnything(x:Any):String = {
x match {
case "Exactly" => "An exact match!"
case s:String => "A String: " + s
case i:Int if (i < 20)
=> s"Int < 20: $i"
case p:Person => s"A person ${p.name}"
case _ => "I don't know what!"
}
}
// from: Atomic Scala v1.1

46. def findCatsCalledBob(x:Cat):String = {
x match {
case Cat("Bob", age)
=> s"Got $age y/o cat called Bob"
case _ => "I don't know what"
}
}
// from: My own Brain

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54. val maybeFirstName : Option[String] =
Some("Mark")
val maybeSurname : Option[String] = None
// from: http://www.markhneedham.com/blog/2011/09/15/scala-for-
// comprehensions-with-options/

55. case class Person(firstName:String,
surname:String)
val maybeFirstName : Option[String] =
Some("Mark")
val maybeSurname : Option[String] = None
for { firstName <- maybeFirstName;
surname <- maybeSurname }
yield Person(firstName, surname)
// res01: Option[Person] = None
// from: http://www.markhneedham.com/blog/2011/09/15/scala-for-
// comprehensions-with-options/

56. case class Person(firstName:String,
surname:String)
val maybeFirstName : Option[String] =
Some("Mark")
val maybeSurname : Option[String] =
Some("Needham")
for { firstName <- maybeFirstName;
surname <- maybeSurname }
yield Person(firstName, surname)
// res01: Option[Person] =
Some(Person(Mark,Needham)
// from: http://www.markhneedham.com/blog/2011/09/15/scala-for-
// comprehensions-with-options/

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59. val maybeFirstName : Option[String] =
Some("me")
val maybeSurname : Option[String] = None
val result = maybeFirstName.map(_.toUpperCase)
// result : Option[String] = Some(ME)
val result = maybeSurame.map(_.toUpperCase)
// result: Option[String] = None
// from: http://alvinalexander.com/
// scala/collection-scala-flatmap-examples-
// map-flatten

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61. val strings = Seq("1", "2", "foo", "3", "bar")
strings: Seq[java.lang.String]
= List(1, 2, foo, 3, bar)
strings.map(toInt)
res0: Seq[Option[Int]] = List(Some(1),
Some(2), None, Some(3), None)
strings.flatMap(toInt)
res1: Seq[Int] = List(1, 2, 3)
// from: http://alvinalexander.com/
// scala/collection-scala-flatmap-examples-
// map-flatten

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63. case class Person(name: String,
isMale : Boolean, children: Person*)
val lara = Person("Lara", false)
val bob = Person("Bob", true)
val julie = Person("Julie", false, lara, bob)
val persons = List(lara, bob, julie)
persons filter (p => !p.isMale)
res0: List[worksheet2.Person] =
List(Person(Lara,false,WrappedArray()),
Person(Julie,false,WrappedArray(...)))
// from: Programming in Scala (2nd Ed.)

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65. val result = for {
n <- v // GENERATOR
if n < 10
valueToYield = n
} yield valueToYield
// from: Atomic Scala v.1.1

66. val result = for {
n <- v
if n < 10 // FILTER
valueToYield = n
} yield valueToYield
// from: Atomic Scala v.1.1

67. val result = for {
n <- v
if n < 10
valueToYield = n // DEFINITION
} yield valueToYield
// from: Atomic Scala v.1.1

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69. // Single Generator plus filter?
val v = Vector(1,2,3,5,6,7,8,10,13,14,17)
val result = for {
n <- v
if n % 2 == 0
} yield n * 2
// Desugars to:
val resultMap =
v.withFilter(n => n % 2 == 0)
.map(n => n * 2)
// res1: Vector(4,12,16,20,28)
// from: My Own Brain

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71. // Multiple Generators
val v = Vector(1,2,3,5,6,7,8,10,13,14,17)
val w = Vector(1)
val result = for {
x <- v
y <- w
} yield x == y
// Desugars to:
val resultMap2 =
v.flatMap{ x => w.map{ y => x == y } }
// res2: Vector(true, false, false, false,…)
// from: My Own Brain

72. // Multiple Generators
val v = Vector(1,2,3,5,6,7,8,10,13,14,17)
val w = Vector(1)
val result = for {
x <- v
y <- w
} yield x == y
// Desugars to:
val resultMap2 =
v.map{ x => w.map{ y => x == y } }
// res2: Vector(Vector(true), Vector(false),…)
// from: My Own Brain

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75. Tips:
• Read closely. (Slowly)
• Beware your Java-sense
• But don’t ignore it
• Unlearning is HARD,
and it HURTS
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76. • Atomic Scala (Eckel & Marsh)
• The Scala Koans
• Scala for the Impatient (Horstmann)
• Twitter’s Scala School
• Introduction to Functional Programming
(Coursera)
• Programming in Scala (2nd Ed.) (Odersky,
Venners, Spoon)
• The Scala Language Specification
(Seriously)
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77. • Implicits
• Type Classes
• Learn you a Haskell
• Revisit
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