This assignment is a continuation of the previous one. You are to write the same library from Homework #2 but implement versions in Java and Standard ML. Readings: Read as many on-line tutorials or book chapters on Java and ML as is reasonable without seriously impacting your personal life.

The libraries for this assignment will be built as follows:

• A Java class called edu.lmu.cs.your_login_name.util.ListUtil with a private constructor, and static methods only.
• A Standard ML structure called ListUtil.

As in the previous homework assignment, a few sample test cases will tell you how the methods should work (in some cases, at least). Note that in no way is this list anywhere near a complete set of test cases. You will be expected to submit a much richer set of test cases.

ML

Wrap up your six ML functions in a structure, something like this:

structure ListUtil = struct
  fun rotate ...
  fun right_reduce ...
  fun descending_integer_squares ...
  fun partial_filter ...
  fun flatten ...
  fun histogram ...
end

I say "something like" because you may find it advantageous, as I did, to use local and val instead of fun in places.

ML doesn't really have a popular unit testing framework, so you'll want to write an assert method yourself:

assert (descending_integer_squares [4, 3, 2, 1, ~10] = [100, 16, 9, 4, 1]);

assert (partial_filter op>= 7 [] = 0);
assert (partial_filter op>= 7 [5, 8, 11, 20, 9, 1, 6, 10] = 3);
assert (partial_filter op<= 30 [5, 8, 11, 20, 9, 1, 6, 10] = 0);
assert (partial_filter op<= 19 [5, 8, 11, 20, 9, 1, 6, 10] = 1);
assert (partial_filter op= 5 [5, 8, 11, 5, 9, 1, 6, 10] = 2);

assert (histogram [4, 50, 6, 12, 4, 6, 12, 12, 12, 4]
  = [(4,3),(50,1),(6,2),(12,4)]);

assert (rotate 0 [] = []);
assert (rotate 7 [1, 2, 3, 4, 5, 6, 7, 8, 9] = [3, 4, 5, 6, 7, 8, 9, 1, 2]);
assert (rotate 900007 [1, 2, 3, 4, 5, 6, 7, 8, 9] = [3, 4, 5, 6, 7, 8, 9, 1, 2]);

assert (flatten [[1], [2, 3], [], [4, 5, 6, 7]] = [1, 2, 3, 4, 5, 6, 7]);

assert (right_reduce op+ [4, 5, 6, 2] = 17);
assert (right_reduce op- [4, 5, 6, 2] = 3);

Java

ListUtil.java should contain a utility class with a private constructor and the six methods all static. In the spirit of Java, we really should make all of the methods generic. In this case your class will look like this:

package ...
import ...
public class ListUtil {
    public static interface BinaryPredicate<S, T> {
        boolean evaluate(S x, T y);
    }
    public static interface BinaryFunction<S, T, U> {
        U evaluate(S x, T y);
    }
    private ListUtil() {}
    public static <S, T> int partialFilter(BinaryPredicate<S, T> p, S x, List<T> a) {...}
    public static List<?> flatten(List<?> a) {...}
    public static <T> Map<T, Integer> histogram(List<T> a) {...}
    public static <T> List<T> rotate(int n, List<T> a) {...}
    public static <T> T rightReduce(BinaryFunction<T, T, T> f, List<T> a) {...}
    public static List<Integer> descendingIntegerSquares(List<Integer> a) {...}
}

If you prefer, you could deal entirely with Objects and see how your Java code plays out.

Since Java is the language most everyone already knows, I'll leave it to you to come up with a good test suite. You must use JUnit here; it is an industry de facto standard.

Your sources should be organized as follows:

homework
  cmsi386
    src
      main
        java
          edu
            lmu
              cs
                ListUtil.java
        ml
          ListUtil.sml
      test
        java
          edu
            lmu
              cs
                ListUtilTest.java (JUnit test)
        ml
          ListUtilTest.sml

Submit your solutions on hardcopy, in a single stapled packet of 8.5" x 11" sheets.

• Submissions that are not exactly in the form above will be downgraded heavily. The directory structure must be exactly as shown above, and all files must be named exactly as shown above, etc.
• Code that does not compile will get a zero.