Added Scala examples

Author: ZheniaTrochun

Scala/.gitignore

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+.idea/
+target/
+*.iml

Scala/1-functor.scala

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+/**
+  * Simple functor example
+  */
+
+case class Functor[A](x: A) {
+  def map[B](f: (A) => B): Functor[B] = Functor(f(x))
+}
+
+object Example {
+
+  def main(args: Array[String]): Unit = {
+    val functor = Functor(2)
+
+    println("Functor rules")
+
+    println("1. functor.map(x => x) = functor")
+    println(s"functor.map(x => x) = ${functor.map(x => x)}")
+    println(s"functor = $functor")
+
+    println("2. functor.map(x => f(g(x))) = functor.map(g).map(f)")
+    println(s"functor.map(x => f(g(x))) = ${functor.map(x => (x * 2) * 3)}")
+    println(s"functor.map(g).map(f) = ${functor.map(_ * 2).map(_ * 3)}")
+
+  }
+}

Scala/2-not-functor.scala

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+/**
+  * NOT a functor because map method returns just value, not ValueMapper
+  */
+
+case class ValueMapper[A](x: A) {
+  def map[B](f: (A) => B): B =
+    f(x)
+}
+
+object NotFunctorExample {
+
+  def main(args: Array[String]): Unit = {
+    val mapper = ValueMapper("Hello" -> 123)
+
+    println(mapper.map(_._1.toUpperCase))
+  }
+}

Scala/3-maybe.scala

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+case class Maybe[A](x: Option[A]) {
+  def map[B](f: (A) => B): Maybe[B] =
+    Maybe(x.map(f))
+
+  def isNothing = x.isEmpty
+
+  override def toString: String =
+    if (isNothing) "Maybe(Nothing)"
+    else s"Maybe(${x.get})"
+}
+
+object Maybe {
+  def apply[A](x: A): Maybe[A] = Maybe(Some(x))
+
+  def empty[A]: Maybe[A] = Maybe[A](None)
+}
+
+object ExampleMaybe {
+
+  def main(args: Array[String]): Unit = {
+    val empty = Maybe.empty[Int]
+    val notEmpty = Maybe(2)
+
+    println(s"Expect Nothing, actual = ${empty.map(_ => 3)}")
+    println(s"Expect Maybe(3), actual = ${notEmpty.map(_ => 3)}")
+  }
+}

Scala/README.md

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+## Scala examples of Functor
+Some great articles:
+1. [What is a functor?](https://medium.com/@dtinth/what-is-a-functor-dcf510b098b6)
+2. [What's NOT a functor](https://medium.com/@dtinth/what-s-not-a-functor-57a081131555)