Fix empty exercises

Author: AdrianRaFo

src/main/scala/scalatutorial/sections/LazyEvaluation.scala

@@ -209,6 +209,18 @@ object LazyEvaluation extends ScalaTutorialSection {
    *   lazy val x = expr
    * }}}
    *
+   * = Lazy Vals and Streams =
+   *
+   * Using a lazy value for `tail`, `Stream.cons` can be implemented more efficiently:
+   *
+   * {{{
+   *   def cons[T](hd: T, tl: => Stream[T]) = new Stream[T] {
+   *     def head = hd
+   *     lazy val tail = tl
+   *     …
+   *   }
+   * }}}
+   *
    * == Exercise ==
    */
   def lazyVal(res0: String): Unit = {
@@ -223,18 +235,4 @@ object LazyEvaluation extends ScalaTutorialSection {
     builder.result() shouldBe res0
   }
 
-  /**
-   * = Lazy Vals and Streams =
-   *
-   * Using a lazy value for `tail`, `Stream.cons` can be implemented more efficiently:
-   *
-   * {{{
-   *   def cons[T](hd: T, tl: => Stream[T]) = new Stream[T] {
-   *     def head = hd
-   *     lazy val tail = tl
-   *     …
-   *   }
-   * }}}
-   */
-  def nothing(): Unit = ()
 }

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

@@ -141,19 +141,19 @@ object StructuringInformation extends ScalaTutorialSection {
    * the possible case of symbols is fixed. The compiler can leverage this
    * knowledge to warn us if we write code that does not handle ''all''
    * the cases:
-   */
-  def unexhaustive(): Unit = {
-    sealed trait Symbol
-    case class Note(name: String, duration: String, octave: Int) extends Symbol
-    case class Rest(duration: String)                            extends Symbol
-
-    def nonExhaustiveDuration(symbol: Symbol): String =
-      symbol match {
-        case Rest(duration) => duration
-      }
-  }
-
-  /**
+   * {{{
+   * def unexhaustive(): Unit = {
+   * sealed trait Symbol
+   * case class Note(name: String, duration: String, octave: Int) extends Symbol
+   * case class Rest(duration: String)                            extends Symbol
+   *
+   * def nonExhaustiveDuration(symbol: Symbol): String =
+   *   symbol match {
+   *     case Rest(duration) => duration
+   *   }
+   * }
+   *}}}
+   *
    * Try to run the above code to see how the compiler informs us that
    * we don’t handle all the cases in `nonExhaustiveDuration`.
    *