Scala : add scala/example

3 files changed, 206 insertions, 0 deletions

diff --git a/Scala/example/src/main/scala/common/package.scala b/Scala/example/src/main/scala/common/package.scala
new file mode 100644
index 0000000..f1c74c3
--- /dev/null
+++ b/Scala/example/src/main/scala/common/package.scala
@@ -0,0 +1,40 @@
+import java.io.File
+
+package object common {
+
+  /** An alias for the `Nothing` type.
+   *  Denotes that the type should be filled in.
+   */
+  type ??? = Nothing
+
+  /** An alias for the `Any` type.
+   *  Denotes that the type should be filled in.
+   */
+  type *** = Any
+
+  
+  /**
+   * Get a child of a file. For example,
+   * 
+   *   subFile(homeDir, "b", "c")
+   * 
+   * corresponds to ~/b/c
+   */
+  def subFile(file: File, children: String*) = {
+    children.foldLeft(file)((file, child) => new File(file, child))
+  }
+
+  /**
+   * Get a resource from the `src/main/resources` directory. Eclipse does not copy
+   * resources to the output directory, then the class loader cannot find them.
+   */
+  def resourceAsStreamFromSrc(resourcePath: List[String]): Option[java.io.InputStream] = {
+    val classesDir = new File(getClass.getResource(".").toURI)
+    val projectDir = classesDir.getParentFile.getParentFile.getParentFile.getParentFile
+    val resourceFile = subFile(projectDir, ("src" :: "main" :: "resources" :: resourcePath): _*)
+    if (resourceFile.exists)
+      Some(new java.io.FileInputStream(resourceFile))
+    else
+      None
+  }
+}
diff --git a/Scala/example/src/main/scala/example/Lists.scala b/Scala/example/src/main/scala/example/Lists.scala
new file mode 100644
index 0000000..4e5feee
--- /dev/null
+++ b/Scala/example/src/main/scala/example/Lists.scala
@@ -0,0 +1,42 @@
+package example
+
+import common._
+
+object Lists {
+  /**
+   * This method computes the sum of all elements in the list xs. There are
+   * multiple techniques that can be used for implementing this method, and
+   * you will learn during the class.
+   *
+   * For this example assignment you can use the following methods in class
+   * `List`:
+   *
+   *  - `xs.isEmpty: Boolean` returns `true` if the list `xs` is empty
+   *  - `xs.head: Int` returns the head element of the list `xs`. If the list
+   *    is empty an exception is thrown
+   *  - `xs.tail: List[Int]` returns the tail of the list `xs`, i.e. the the
+   *    list `xs` without its `head` element
+   *
+   *  ''Hint:'' instead of writing a `for` or `while` loop, think of a recursive
+   *  solution.
+   *
+   * @param xs A list of natural numbers
+   * @return The sum of all elements in `xs`
+   */
+  def sum(xs: List[Int]): Int = ???
+
+  /**
+   * This method returns the largest element in a list of integers. If the
+   * list `xs` is empty it throws a `java.util.NoSuchElementException`.
+   *
+   * You can use the same methods of the class `List` as mentioned above.
+   *
+   * ''Hint:'' Again, think of a recursive solution instead of using looping
+   * constructs. You might need to define an auxiliary method.
+   *
+   * @param xs A list of natural numbers
+   * @return The largest element in `xs`
+   * @throws java.util.NoSuchElementException if `xs` is an empty list
+   */
+  def max(xs: List[Int]): Int = ???
+}
diff --git a/Scala/example/src/test/scala/example/ListsSuite.scala b/Scala/example/src/test/scala/example/ListsSuite.scala
new file mode 100644
index 0000000..4a52667
--- /dev/null
+++ b/Scala/example/src/test/scala/example/ListsSuite.scala
@@ -0,0 +1,124 @@
+package example
+
+import org.scalatest.FunSuite
+
+import org.junit.runner.RunWith
+import org.scalatest.junit.JUnitRunner
+
+/**
+ * This class implements a ScalaTest test suite for the methods in object
+ * `Lists` that need to be implemented as part of this assignment. A test
+ * suite is simply a collection of individual tests for some specific
+ * component of a program.
+ *
+ * A test suite is created by defining a class which extends the type
+ * `org.scalatest.FunSuite`. When running ScalaTest, it will automatically
+ * find this class and execute all of its tests.
+ *
+ * Adding the `@RunWith` annotation enables the test suite to be executed
+ * inside eclipse using the built-in JUnit test runner.
+ *
+ * You have two options for running this test suite:
+ * 
+ * - Start the sbt console and run the "test" command
+ * - Right-click this file in eclipse and chose "Run As" - "JUnit Test"
+ */
+@RunWith(classOf[JUnitRunner])
+class ListsSuite extends FunSuite {
+
+  /**
+   * Tests are written using the `test` operator which takes two arguments:
+   *
+   * - A description of the test. This description has to be unique, no two
+   *   tests can have the same description.
+   * - The test body, a piece of Scala code that implements the test
+   *
+   * The most common way to implement a test body is using the method `assert`
+   * which tests that its argument evaluates to `true`. So one of the simplest
+   * successful tests is the following:
+   */
+  test("one plus one is two")(assert(1 + 1 == 2))
+
+
+  /**
+   * In Scala, it is allowed to pass an argument to a method using the block
+   * syntax, i.e. `{ argument }` instead of parentheses `(argument)`.
+   *
+   * This allows tests to be written in a more readable manner:
+   */
+  test("one plus one is three?") {
+    assert(1 + 1 == 3) // This assertion fails! Go ahead and fix it.
+  }
+
+
+  /**
+   * One problem with the previous (failing) test is that ScalaTest will
+   * only tell you that a test failed, but it will not tell you what was
+   * the reason for the failure. The output looks like this:
+   *
+   * {{{
+   *    [info] - one plus one is three? *** FAILED ***
+   * }}}
+   *
+   * This situation can be improved by using a special equality operator
+   * `===` instead of `==` (this is only possible in ScalaTest). So if you
+   * run the next test, ScalaTest will show the following output:
+   *
+   * {{{
+   *    [info] - details why one plus one is not three *** FAILED ***
+   *    [info]   2 did not equal 3 (ListsSuite.scala:67)
+   * }}}
+   *
+   * We recommend to always use the `===` equality operator when writing tests.
+   */
+  test("details why one plus one is not three") {
+    assert(1 + 1 === 3) // Fix me, please!
+  }
+
+
+  /**
+   * In order to test the exceptional behavior of a methods, ScalaTest offers
+   * the `intercept` operation.
+   *
+   * In the following example, we test the fact that the method `intNotZero`
+   * throws an `IllegalArgumentException` if its argument is `0`.
+   */
+  test("intNotZero throws an exception if its argument is 0") {
+    intercept[IllegalArgumentException] {
+      intNotZero(0)
+    }
+  }
+
+  def intNotZero(x: Int): Int = {
+    if (x == 0) throw new IllegalArgumentException("zero is not allowed")
+    else x
+  }
+
+
+  /**
+   * Now we finally write some tests for the list functions that have to be
+   * implemented for this assignment. We fist import all members of the
+   * `List` object.
+   */ 
+  import Lists._
+  
+
+  /**
+   * We only provide two very basic tests for you. Write more tests to make
+   * sure your `sum` and `max` methods work as expected.
+   *
+   * In particular, write tests for corner cases: negative numbers, zeros,
+   * empty lists, lists with repeated elements, etc.
+   *
+   * It is allowed to have multiple `assert` statements inside one test,
+   * however it is recommended to write an individual `test` statement for
+   * every tested aspect of a method.
+   */
+  test("sum of a few numbers") {
+    assert(sum(List(1,2,0)) === 3)
+  }
+  
+  test("max of a few numbers") {
+    assert(max(List(3, 7, 2)) === 7)
+  }
+}