// CS111 Lab 13 Spring 2000
public class ListOfListsLab {

  // hack for being able to refer to IntList and IntListList methods
  // by abbreviations IL and ILL respectively
  private static IntListOps IL;
  private static IntListListOps ILL;
  
  public static IntList mapSum (IntListList nss) {
    if (ILL.isEmpty(nss)) {
      return IL.empty();
    } else {
      return IL.prepend(IL.sum(ILL.head(nss)), mapSum(ILL.tail(nss)));
    }
  }
  
  public static IntListList mapMapDouble (IntListList nss) {
    if (ILL.isEmpty(nss)) {
      return ILL.empty();
    } else {
      return ILL.prepend(IL.mapDouble(ILL.head(nss)), mapMapDouble(ILL.tail(nss)));
    }
  }

  public static IntListList subsequences (IntList ns) {
    if (IL.isEmpty(ns)) {
      return ILL.prepend(IL.empty(),ILL.empty());
    } else {
      IntListList partialSubsequences = subsequences(IL.tail(ns));
      return ILL.append(mapPrepend(IL.head(ns), partialSubsequences),
                         partialSubsequences);
    }
  }
  
  public static IntListList combination (IntListList nss) {
    if (ILL.isEmpty(nss)) {
      return ILL.prepend(IL.empty(), ILL.empty());
    } else {
      return mapMapPrepend(ILL.head(nss), combination(ILL.tail(nss)));
    }
  }
  
  public static IntListList mapMapPrepend (IntList ns, IntListList nss) {
    if (IL.isEmpty(ns)) {
      return ILL.empty();
    } else {
      return ILL.append(mapPrepend(IL.head(ns), nss),
                         mapMapPrepend(IL.tail(ns), nss));
    }
  }
  
  public static IntListList mapPrepend (int n, IntListList nss) {
    if (ILL.isEmpty(nss)) {
      return ILL.empty();
    } else {
      return ILL.prepend(IL.prepend(n, ILL.head(nss)),
                          mapPrepend(n, ILL.tail(nss)));
    }
  }

}