Add more exercises

Author: julienrf

src/main/scala/scalatutorial/sections/DefinitionsAndEvaluation.scala

@@ -204,7 +204,19 @@ object DefinitionsAndEvaluation extends ScalaTutorialSection {
     * corresponding parameter is unused in the evaluation of the function body.
     *
     * Scala normally uses call-by-value.
+    *
+    * = Exercise =
+    *
+    * Complete the following definition of the `triangleArea` function,
+    * which takes a triangle base and height as parameters and returns
+    * its area:
     */
-  def nothing(): Unit = ()
+  def triangleAreaExercise(res0: Double, res1: Double): Unit = {
+    def triangleArea(base: Double, height: Double): Double =
+      base * height / res0
+
+    triangleArea(3, 4) shouldBe 6
+    triangleArea(5, 6) shouldBe res1
+  }
 
 }

src/main/scala/scalatutorial/sections/ImperativeProgramming.scala

@@ -320,14 +320,33 @@ object ImperativeProgramming extends ScalaTutorialSection {
     * Example:
     *
     * {{{
-    *   for (i <- 1 until 3; j <- "abc") println(i + " " + j)
+    *   for (i <- 1 until 3; j <- "abc") println(s"$i $j")
     * }}}
     *
     * translates to:
     *
     * {{{
-    *   (1 until 3) foreach (i => "abc" foreach (j => println(i + " " + j)))
+    *   (1 until 3) foreach (i => "abc" foreach (j => println(s"$i $j")))
     * }}}
+    *
+    * = Exercise =
+    *
+    * Complete the following imperative implementation of `factorial`:
     */
-  def nothing(): Unit = ()
+  def factorialExercise(res0: Int, res1: Int, res2: Int): Unit = {
+    def factorial(n: Int): Int = {
+      var result = res0
+      var i = res1
+      while (i <= n) {
+        result = result * i
+        i = i + res2
+      }
+      result
+    }
+
+    factorial(2) shouldBe 2
+    factorial(3) shouldBe 6
+    factorial(4) shouldBe 24
+    factorial(5) shouldBe 120
+  }
 }

src/main/scala/scalatutorial/sections/LexicalScopes.scala

@@ -267,6 +267,22 @@ object LexicalScopes extends ScalaTutorialSection {
     * {{{
     *   $ scala Hello
     * }}}
+    *
+    * = Exercise =
+    *
     */
-  def nothing(): Unit = ()
+  def objectScopes(res0: Int): Unit = {
+    object Foo {
+      val x = 1
+    }
+    object Bar {
+      val x = 2
+    }
+    object Baz {
+      import Bar.x
+      val y = x + Foo.x
+    }
+
+    Baz.y shouldBe res0
+  }
 }

src/main/scala/scalatutorial/sections/ObjectOrientedProgramming.scala

@@ -304,7 +304,7 @@ object ObjectOrientedProgramming extends ScalaTutorialSection {
     * a computation model based on substitution. Now we extend this
     * model to classes and objects.
     *
-    * How is an instantiation of the class `new C(e1, …, en)` evaluted?
+    * How is an instantiation of the class `new C(e1, …, en)` evaluated?
     *
     * The expression arguments `e1, …, en`
     * are evaluated like the arguments of a normal function. That's it.
@@ -627,6 +627,35 @@ object ObjectOrientedProgramming extends ScalaTutorialSection {
   *   val y: String = null // y: String
   *   val z: Int = null    // error: type mismatch
   * }}}
+  *
+  * = Exercise =
+  *
+  * The following `Reducer` abstract class defines how to
+  * reduce a list of values into a single value by starting
+  * with an initial value and combining it with each element
+  * of the list:
   */
-  def nothing(): Unit = ()
+  def reducer(res0: Int, res1: Int): Unit = {
+    abstract class Reducer(init: Int) {
+      def combine(x: Int, y: Int): Int
+      def reduce(xs: List[Int]): Int =
+        xs match {
+          case Nil => init
+          case y :: ys => combine(y, reduce(ys))
+        }
+    }
+
+    object Product extends Reducer(1) {
+      def combine(x: Int, y: Int): Int = x * y
+    }
+
+    object Sum extends Reducer(0) {
+      def combine(x: Int, y: Int): Int = x + y
+    }
+
+    val nums = List(1, 2, 3, 4)
+
+    Product.reduce(nums) shouldBe res0
+    Sum.reduce(nums) shouldBe res1
+  }
 }

src/main/scala/scalatutorial/sections/PolymorphicTypes.scala

@@ -419,7 +419,21 @@ object PolymorphicTypes extends ScalaTutorialSection {
     *
     *  - covariant type parameters may appear in lower bounds of method type parameters
     *  - contravariant type parameters may appear in upper bounds of method
+    *
+    * = Exercise =
+    *
+    * Complete the following implementation of the `size` function that returns
+    * the size of a given list.
     */
-  def nothing(): Unit = ()
+  def sizeExercise(res0: Int, res1: Int): Unit = {
+    def size[A](xs: List[A]): Int =
+      xs match {
+        case Nil => res0
+        case y :: ys => res1 + size(ys)
+      }
+    size(Nil) shouldBe 0
+    size(List(1, 2)) shouldBe 2
+    size(List("a", "b", "c")) shouldBe 3
+  }
 
 }

src/main/scala/scalatutorial/sections/StandardLibrary.scala

@@ -261,21 +261,32 @@ object StandardLibrary extends ScalaTutorialSection {
     *
     * === Manipulating `Either[A, B]` Values ===
     *
-    * `Either` has `map` and `flatMap`. These methods transform the `Right`
-    * case only. Way say that `Either` is “right biased”:
+    * Since Scala 2.12, `Either` has `map` and `flatMap`. These methods
+    * transform the `Right` case only. Way say that `Either` is “right biased”:
     *
     * {{{
     *   Right(1).map((x: Int) => x + 1) shouldBe Right(2)
     *   Left("foo").map((x: Int) => x + 1) shouldBe Left("foo")
     * }}}
     *
-    * `Either` also has a `filterOrElse` method that turn a `Right` value
+    * `Either` also has a `filterOrElse` method that turns a `Right` value
     * into a `Left` value if it does not satisfy a given predicate:
     *
     * {{{
     *   Right(1).filterOrElse(x => x % 2 == 0, "Odd value") shouldBe Left("Odd value")
     * }}}
+    *
+    * However, prior to Scala 2.12, `Either` was “unbiased”. You had to explicitly
+    * specify which “side” (`Left` or `Right`) you wanted to `map`:
     */
-  def nothing(): Unit = ()
+  def either(res0: Either[String, Int], res1: Either[String, Int]): Unit = {
+    def triple(x: Int): Int = 3 * x
+
+    def tripleEither(x: Either[String, Int]): Either[String, Int] =
+      x.right.map(triple)
+
+    tripleEither(Right(1)) shouldBe res0
+    tripleEither(Left("not a number")) shouldBe res1
+  }
 
 }

src/main/scala/scalatutorial/sections/StructuringInformation.scala

@@ -42,6 +42,9 @@ object StructuringInformation extends ScalaTutorialSection {
     *   val c3 = Note("C", "Quarter", 3)
     * }}}
     *
+    * `c3` is a value that aggregates the arguments passed to the `Note`
+    * constructor.
+    *
     * Then, you can retrieve the information carried by each ''member'' (`name`,
     * `duration` and `octave`) by using the dot notation:
     */
@@ -221,6 +224,28 @@ object StructuringInformation extends ScalaTutorialSection {
     * {{{
     *   case class Note(name: String, duration: String, octave: Int) extends Symbol
     * }}}
+    *
+    * = Exercise =
+    *
+    * Consider the following algebraic data type that models note durations.
+    * Complete the implementation of the function `fractionOfWhole`, which
+    * takes as parameter a duration and returns the corresponding fraction
+    * of the `Whole` duration.
     */
-  def nothing(): Unit = ()
+  def adts(res0: Double, res1: Double): Unit = {
+    sealed trait Duration
+    case object Whole extends Duration
+    case object Half extends Duration
+    case object Quarter extends Duration
+
+    def fractionOfWhole(duration: Duration): Double =
+      duration match {
+        case Whole => 1.0
+        case Half => res0
+        case Quarter => res1
+      }
+
+    fractionOfWhole(Half) shouldBe 0.5
+    fractionOfWhole(Quarter) shouldBe 0.25
+  }
 }

src/main/scala/scalatutorial/sections/TermsAndTypes.scala

@@ -164,13 +164,23 @@ object TermsAndTypes extends ScalaTutorialSection {
   /**
     * = Common Types =
     *
-    *  - `Int`: 32-bit integers
-    *  - `Double`: 64-bit floating point numbers
-    *  - `Boolean`: boolean values
-    *  - `String`: text
+    *  - `Int`: 32-bit integers (e.g. `1`, `23`, `456`)
+    *  - `Double`: 64-bit floating point numbers (e.g. `1.0`, `2.3`, `4.56`)
+    *  - `Boolean`: boolean values (`true` and `false`)
+    *  - `String`: text (e.g. `"foo"`, `"bar"`)
     *
-    *  Note that type names always begin with an upper case.
+    * Note that type names always begin with an upper case letter.
+    *
+    * = Exercise =
+    *
+    * Here are some more methods of standard types. Can you guess what they do?
     */
-  def nothing(): Unit = ()
+  def moreMethods(res0: String, res1: Boolean, res2: String): Unit = {
+    16.toHexString shouldBe res0
+    (0 to 10).contains(10) shouldBe true
+    (0 until 10).contains(10) shouldBe res1
+    "foo".drop(1) shouldBe "oo"
+    "bar".take(2) shouldBe res2
+  }
 
 }

src/test/scala/scalatutorial/sections/DefinitionsAndEvaluationSpec.scala

@@ -16,4 +16,8 @@ class DefinitionsAndEvaluationSpec extends Spec with Checkers {
     check(Test.testSuccess(DefinitionsAndEvaluation.areaExercise _, 314.159 :: HNil))
   }
 
+  def `check triangle area`: Unit = {
+    check(Test.testSuccess(DefinitionsAndEvaluation.triangleAreaExercise _, 2.0 :: 15.0 :: HNil))
+  }
+
 }

src/test/scala/scalatutorial/sections/HigherOrderFunctionsSpec.scala

@@ -8,8 +8,8 @@ import shapeless.HNil
 
 class HigherOrderFunctionsSpec extends Spec with Checkers {
 
-  def `check tail rec sum`: Unit = {
-    check(Test.testSuccess(HigherOrderFunctions.tailRecSum _, 1 :: 0 :: HNil))
-  }
+//  def `check tail rec sum`: Unit = {
+//    check(Test.testSuccess(HigherOrderFunctions.tailRecSum _, 1 :: 0 :: HNil))
+//  }
 
 }