Merge pull request #45 from ldrygala/scala-37-currying

SCALA-37 currying intro

Author: lor6

core-scala/src/test/scala/com/baeldung/scala/currying/CurryingUnitTest.scala

@@ -0,0 +1,110 @@
+package com.baeldung.scala.currying
+
+import org.junit.Test
+import org.scalatest.Matchers
+
+class CurryingUnitTest extends Matchers {
+
+  @Test
+  def givenMultipleArgumentsFunction_whenCurried_thenReturnCurriedFunction() {
+    val sum: (Int, Int) => Int = (x, y) => x + y
+    val curriedSum: Int => Int => Int = sum.curried
+
+    sum(1, 2) shouldBe 3
+    curriedSum(1)(2) shouldBe 3
+  }
+
+  @Test
+  def givenMultipleArgumentsMethod_whenCurried_thenReturnCurriedFunction() {
+    def sum(x: Int, y: Int): Int = x + y
+
+    val curriedSum: Int => Int => Int = (sum _).curried
+
+    sum(1, 2) shouldBe 3
+    curriedSum(1)(2) shouldBe 3
+  }
+
+  @Test
+  def givenMultipleArgumentListsMethod_whenCurried_thenReturnCurriedFunction() {
+    def sum(x: Int)(y: Int): Int = x + y
+
+    val curriedSum: Int => Int => Int = sum
+
+    sum(1)(2) shouldBe 3
+    curriedSum(1)(2) shouldBe 3
+  }
+
+  @Test
+  def givenCurriedFunction_whenPartialApplied_thenReturnLowerArityFunction() {
+    val sum: Int => Int => Int = x => y => x + y
+    val increment: Int => Int = sum(1)
+
+    increment(1) shouldBe 2
+  }
+
+  @Test
+  def givenMultipleArgumentListsMethod_whenPartialApplied_thenReturnLowerArityMethod() {
+    def sum(x: Int)(y: Int): Int = x + y
+
+    val increment: Int => Int = sum(1)
+
+    increment(1) shouldBe 2
+  }
+
+  @Test
+  def givenMultipleArgumentsFindMethod_whenCalled_thenPredicateFunctionNeedsExplicitType() {
+    def find[A](xs: List[A], predicate: A => Boolean): Option[A] = {
+      xs match {
+        case Nil => None
+        case head :: tail =>
+          if (predicate(head)) Some(head) else find(tail, predicate)
+      }
+    }
+
+    find(List(1, 2, 3), (x: Int) => x % 2 == 0) shouldBe Some(2)
+  }
+
+  @Test
+  def givenMultipleArgumentListFindMethod_whenCalled_thenPredicateFunctionDoesNotNeedExplicitType() {
+    def find[A](xs: List[A])(predicate: A => Boolean): Option[A] = {
+      xs match {
+        case Nil => None
+        case head :: tail =>
+          if (predicate(head)) Some(head) else find(tail)(predicate)
+      }
+    }
+
+    find(List(1, 2, 3))(x => x % 2 == 0) shouldBe Some(2)
+  }
+
+  @Test
+  def givenGenericMultipleArgumentListSumMethod_whenPartialApplied_thenReturnSimpleMethods() {
+    def sumF(f: Int => Int)(x: Int, y: Int): Int = f(x) + f(y)
+    val sum: (Int, Int) => Int = sumF(identity)
+    val sumSquare: (Int, Int) => Int = sumF(x => x * x)
+    val increment: Int => Int = sum.curried(1)
+    val decrement: Int => Int = sum.curried(-1)
+
+    sum(1, 2) shouldBe 3
+    sumSquare(1, 2) shouldBe 5
+    increment(2) shouldBe 3
+    decrement(2) shouldBe 1
+  }
+
+  @Test
+  def givenMultipleArgumentsFunction_whenUseItAsOneArgumentFunction_thenNeedsExplicitArgumentPassing() {
+    val sum: (Int, Int) => Int = (x, y) => x + y
+    val numbers: List[Int] = List(1, 2, 3)
+
+    numbers.map(n => sum(1, n)) shouldBe List(2, 3, 4)
+  }
+
+  @Test
+  def givenCurriedFunction_whenUseItAsOneArgumentFunction_thenDoesNotNeedExplicitArgumentPassing() {
+    val curriedSum: Int => Int => Int = x => y => x + y
+    val numbers: List[Int] = List(1, 2, 3)
+
+    numbers.map(curriedSum(1)) shouldBe List(2, 3, 4)
+  }
+
+}