CS 252

Homework 2

Part 1. For this assignment, you will use Bill Venners' ScalaTest to produce test cases for your solution to homework 1. Here is an example, a test class to check the freeVariables function. Most of you passed that. I give you a starting point for another test to check the renameAvoiding function. I added more test cases to my version that many of you failed.

I had to go back to Scala 2.7.6 to get ScalaTest to work. Bill said he'd try to get it working with the latest Scala 2.8.0, but it may be a few more days before he'll find the time. (Everyone's hw1 code compiled under 2.7.6.)

UPDATE: Bill just posted a fix that works under 2.8.0. See here. I was able to build it by running

svn checkout https://scalatest.dev.java.net/svn/scalatest/branches/app/trunk-for-scala-2.8f --username guest 
cd trunk-for-scala-2.8f
ant
mkdir ~/scalatest-1.0
cp target/dist/lib/scalatest.jar ~/scalatest-1.0

Try this first. The Scala plugin for 2.8 is a lot less flaky than the one for 2.7. (Let me know if you need directions for installing ant.)

Deliverables:

• RenameAvoidingTest.scala with more test cases. Due for first submission.
• SimplifyOnceTest.scala with good coverage of simplifyOnce
• A revised lambda.scala that passes your own test cases. If it also passes mine and gives the right results on fac, powtwo and firstmatches, I will regrade your homework #1 with it. Draft due for first submission.
• A plain text file scalatest.txt with a brief but precise explanation of how the test method uses closures. I want to know what parameters test consumes, which of them are closures, and when they are executed.

Part 2. One advantage of closures is that they allow you to build new control structures. One example is forEachProperty in Lab 8 part 3. Implement this in Scala.

Deliverables:

• A file props.scala with an object Props containing a forEachProperty function and a simple (not ScalaTest) test in main, printing all system properties.

Part 3. This program demonstrates how to animate the insertion sort algorithm. Note that the program has to deal with two challenges of Swing programming:

• An event handler cannot carry out a task of long duration on the event dispatch thread. For that reason, the sort method starts a new thread for animating the algorithm
• Another thread is not allowed to make changes to Swing because Swing is not threadsafe. For that reason, the setProperty method uses EventQueue.invokeLater to make a Runnable that Swing will execute on the event dispatch thread.

Your task is to improve the program in two ways.

a) Eliminate the unsightly anonymous Runnable objects by providing an implicit conversion from ()=>Unit to a Runnable, so that, for example, the sort method can be simplified to

  def sort(e : ActionEvent) {
    val t = new Thread(() => {
      val a = randomNumberArray(10, 100)
      insertionSort(a)
    })
    t.start()
  }

Due for first submission.

b) Write a function

doTogether(tasks : Iterable[()=>Unit])

that executes all tasks in parallel, using Executors.newCachedThreadPool.invokeAll. I could not find a way of converting a Scala Iterable into a java.util.Collection and had to copy the tasks into a Java ArrayList, as I converted them to callables (using Executors.callable).

Demonstrate this function by running the move(next, 0, 1) tasks in parallel, so that the entire slice from j + 1 to i moves together.

At first, I had an inelegant solution where I just added the tasks in the same loop that shifted the array, and it looked quite un-functional. Don't do that. Instead, use slice and map, passing the result to doTogether.

An attempt for doTogether is due for the first submission.

Deliverables:

• A file animate.scala, modified as described, with a function Animation.doTogether that I can test separately