added some scala examples

Author: ZheniaTrochun

Scala/.gitignore

@@ -0,0 +1,3 @@
+.idea/
+target/
+*.iml

Scala/1-callback.scala

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+object Callback {
+
+  def func(data: Option[String], callback: (Either[Exception, String]) => Int): Int =
+    data map {d =>
+      callback(Right(s"Data: $d"))
+    } getOrElse {
+      callback(Left(new Exception("Exception occurred!")))
+    }
+
+  def simpleCallback(input: Either[Exception, String]): Int =
+    input map { s: String =>
+      println(s)
+      1 // ok, status 1
+    } getOrElse {
+      println(s"Data is not present!\n${input.left.get.getMessage}")
+      -1 // NOT ok, status -1
+    }
+
+  def main(args: Array[String]): Unit = {
+    println(s"None status = ${func(None, simpleCallback)}")
+
+    println(s"Some status = ${func(Some("123"), simpleCallback)}")
+  }
+}

Scala/2-closure.scala

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+object Closure {
+  def func(a: String): String => Unit = {
+    val b = "Closure variable"
+
+    (c: String) =>
+      println(s"$a\t$b\t$c")
+  }
+
+  def main(args: Array[String]): Unit = {
+    val f1 = func("Number 1")
+    f1("Number 2")
+
+    val f2 = func("Parameter X")
+    f2("Parameter Y")
+  }
+}

Scala/3-chain.scala

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+object Chain {
+
+  def sum(a: Int) =
+    (b: Int) =>
+      (c: Int) =>
+        a + b + c
+
+  def main(args: Array[String]): Unit = {
+    val f1 = sum(1)(1)
+    val s1 = f1(1)
+    val s2 = f1(2)
+
+    println(s"$s1\t$s2")
+  }
+}

Scala/4-cache.scala

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+object Cache {
+
+//  acts like functor
+  def cached() = {
+    println("Generate cache")
+    var cache: Int Map String = Map.empty[Int, String]
+
+    (a: Int) =>
+      cache.get(a) map { value =>
+        println("Found in cache")
+        value
+      } getOrElse {
+        println("Not found in cache, calculating and saving")
+        val res = a -> s"value $a"
+        cache += res
+        res
+      }
+  }
+
+  def main(args: Array[String]): Unit = {
+    val f1 = cached()
+    f1(1)
+    f1(2)
+    f1(1)
+    f1(2)
+
+    val f2 = cached()
+    f2(1)
+    f2(2)
+    f2(1)
+    f2(2)
+  }
+}

Scala/5-complex.scala

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+/**
+  * Some more complex examples of higher order functions usage
+  * there are `sum` and `product` functions with regular and tail recursive examples
+  * and some generalized functions which can be used for creating `sum` and `product`
+  */
+
+object ComplexExample {
+
+  def sum(f: (Int) => Int)(a: Int, b: Int): Int =
+    if (a > b) 0
+    else f(a) + sum(f)(a + 1, b)
+
+
+  def product(f: (Int) => Int)(a: Int, b: Int): Int =
+    if (a > b) 1
+    else f(a) * product(f)(a + 1, b)
+
+//  tail recursive sum
+  def sum1(f: (Int) => Int)(a: Int, b: Int): Int = {
+    def loop(buf: Int)(curr: Int): Int =
+      if (curr > b) buf
+      else loop(buf + f(curr))(curr + 1)
+
+    loop(0)(a)
+  }
+
+//  tail recursive product
+  def product1(f: (Int) => Int)(a: Int, b: Int): Int = {
+    def loop(buf: Int)(curr: Int): Int =
+      if (curr > b) buf
+      else loop(buf * f(curr))(curr + 1)
+
+    loop(1)(a)
+  }
+
+  def generalized(zero: Int)(combine: (Int, Int) => Int): (Int => Int) => (Int, Int) => Int = {
+    def innerFunc(f: (Int) => Int)(a: Int, b: Int): Int = {
+      if (a > b) zero
+      else combine(f(a), innerFunc(f)(a + 1, b))
+    }
+    innerFunc
+  }
+
+//  tail recursive generalized function
+  def generalized1(zero: Int)(combine: (Int, Int) => Int): (Int => Int) => (Int, Int) => Int = {
+    (f: (Int) => Int) => (a: Int, b: Int) => {
+      def loop(buf: Int)(curr: Int): Int =
+        if (curr > b) buf
+        else loop(combine(buf, f(curr)))(curr + 1)
+
+      loop(zero)(a)
+    }
+  }
+
+  def main(args: Array[String]): Unit = {
+    val identity = (x: Int) => x
+    val square = (x: Int) => x * x
+
+    val generalizedSum = generalized(0)(_ + _)
+    val generalizedSum1 = generalized1(0)(_ + _)
+    println("sum of squares")
+    println(s"sum(x => x * x)(1, 5) = ${sum(square)(1, 5)}")
+    println(s"sum1(x => x * x)(1, 5) = ${sum1(square)(1, 5)}")
+    println(s"generalizedSum(x => x * x)(1, 5) = ${generalizedSum(square)(1, 5)}")
+    println(s"generalizedSum1(x => x * x)(1, 5) = ${generalizedSum1(square)(1, 5)}")
+
+    val generalizedProduct = generalized(1)(_ * _)
+    val generalizedProduct1 = generalized1(1)(_ * _)
+    println("factorial")
+    println(s"product(x => x)(1, 5) = ${product(identity)(1, 5)}")
+    println(s"product1(x => x)(1, 5) = ${product1(identity)(1, 5)}")
+    println(s"generalizedProduct(x => x)(1, 5) = ${generalizedProduct(identity)(1, 5)}")
+    println(s"generalizedProduct1(x => x)(1, 5) = ${generalizedProduct1(identity)(1, 5)}")
+  }
+}