--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/src/main/java/fj/data/List.java	Fri Mar 20 21:04:03 2015 +0900
@@ -0,0 +1,2016 @@
+package fj.data;
+
+import static fj.Bottom.error;
+import fj.F2Functions;
+import fj.Equal;
+import fj.F;
+import fj.F2;
+import fj.F3;
+import fj.Function;
+import fj.Hash;
+import fj.Monoid;
+import fj.Ord;
+import fj.P;
+import fj.P1;
+import fj.P2;
+import fj.Show;
+import fj.Unit;
+import static fj.Function.curry;
+import static fj.Function.constant;
+import static fj.Function.identity;
+import static fj.Function.compose;
+import static fj.P.p;
+import static fj.P.p2;
+import static fj.Unit.unit;
+import static fj.data.Array.mkArray;
+import static fj.data.List.Buffer.*;
+import static fj.data.Option.none;
+import static fj.data.Option.some;
+import static fj.function.Booleans.not;
+import static fj.Ordering.GT;
+import static fj.Ord.intOrd;
+
+import fj.Ordering;
+import fj.control.Trampoline;
+import fj.function.Effect1;
+
+import java.util.AbstractCollection;
+import java.util.Collection;
+import java.util.Iterator;
+import java.util.NoSuchElementException;
+
+/**
+ * Provides an in-memory, immutable, singly linked list.
+ *
+ * @version %build.number%
+ */
+public abstract class List<A> implements Iterable<A> {
+  private List() {
+
+  }
+
+  /**
+   * Returns an iterator for this list. This method exists to permit the use in a <code>for</code>-each loop.
+   *
+   * @return A iterator for this list.
+   */
+  public final Iterator<A> iterator() {
+    return toCollection().iterator();
+  }
+
+  /**
+   * The first element of the linked list or fails for the empty list.
+   *
+   * @return The first element of the linked list or fails for the empty list.
+   */
+  public abstract A head();
+
+  /**
+   * The list without the first element or fails for the empty list.
+   *
+   * @return The list without the first element or fails for the empty list.
+   */
+  public abstract List<A> tail();
+
+  /**
+   * The length of this list.
+   *
+   * @return The length of this list.
+   */
+  public final int length() {
+    return foldLeft(new F<Integer, F<A, Integer>>() {
+      public F<A, Integer> f(final Integer i) {
+        return new F<A, Integer>() {
+          public Integer f(final A a) {
+            return i + 1;
+          }
+        };
+      }
+    }, 0);
+  }
+
+  /**
+   * Returns <code>true</code> if this list is empty, <code>false</code> otherwise.
+   *
+   * @return <code>true</code> if this list is empty, <code>false</code> otherwise.
+   */
+  public final boolean isEmpty() {
+    return this instanceof Nil;
+  }
+
+  /**
+   * Returns <code>false</code> if this list is empty, <code>true</code> otherwise.
+   *
+   * @return <code>false</code> if this list is empty, <code>true</code> otherwise.
+   */
+  public final boolean isNotEmpty() {
+    return this instanceof Cons;
+  }
+
+  /**
+   * Performs a reduction on this list using the given arguments.
+   *
+   * @param nil  The value to return if this list is empty.
+   * @param cons The function to apply to the head and tail of this list if it is not empty.
+   * @return A reduction on this list.
+   */
+  public final <B> B list(final B nil, final F<A, F<List<A>, B>> cons) {
+    return isEmpty() ? nil : cons.f(head()).f(tail());
+  }
+
+  /**
+   * Returns the head of this list if there is one or the given argument if this list is empty.
+   *
+   * @param a The argument to return if this list is empty.
+   * @return The head of this list if there is one or the given argument if this list is empty.
+   */
+  public final A orHead(final P1<A> a) {
+    return isEmpty() ? a._1() : head();
+  }
+
+  /**
+   * Returns the tail of this list if there is one or the given argument if this list is empty.
+   *
+   * @param as The argument to return if this list is empty.
+   * @return The tail of this list if there is one or the given argument if this list is empty.
+   */
+  public final List<A> orTail(final P1<List<A>> as) {
+    return isEmpty() ? as._1() : tail();
+  }
+
+  /**
+   * Returns an option projection of this list; <code>None</code> if empty, or the first element in
+   * <code>Some</code>.
+   *
+   * @return An option projection of this list.
+   */
+  public final Option<A> toOption() {
+    return isEmpty() ? Option.<A>none() : some(head());
+  }
+
+  /**
+   * Returns an either projection of this list; the given argument in <code>Left</code> if empty, or
+   * the first element in <code>Right</code>.
+   *
+   * @param x The value to return in left if this list is empty.
+   * @return An either projection of this list.
+   */
+  public final <X> Either<X, A> toEither(final P1<X> x) {
+    return isEmpty() ? Either.<X, A>left(x._1()) : Either.<X, A>right(head());
+  }
+
+  /**
+   * Returns a stream projection of this list.
+   *
+   * @return A stream projection of this list.
+   */
+  public final Stream<A> toStream() {
+    final Stream<A> nil = Stream.nil();
+    return foldRight(new F<A, F<Stream<A>, Stream<A>>>() {
+      public F<Stream<A>, Stream<A>> f(final A a) {
+        return new F<Stream<A>, Stream<A>>() {
+          public Stream<A> f(final Stream<A> as) {
+            return as.cons(a);
+          }
+        };
+      }
+    }, nil);
+  }
+
+  /**
+   * Returns a array projection of this list.
+   *
+   * @return A array projection of this list.
+   */
+  @SuppressWarnings({"unchecked"})
+  public final Array<A> toArray() {
+    final Object[] a = new Object[length()];
+    List<A> x = this;
+    for (int i = 0; i < length(); i++) {
+      a[i] = x.head();
+      x = x.tail();
+    }
+
+    return mkArray(a);
+  }
+
+  /**
+   * Returns a array projection of this list.
+   *
+   * @param c The class type of the array to return.
+   * @return A array projection of this list.
+   */
+  @SuppressWarnings({"unchecked", "UnnecessaryFullyQualifiedName"})
+  public final Array<A> toArray(final Class<A[]> c) {
+    final A[] a = (A[]) java.lang.reflect.Array.newInstance(c.getComponentType(), length());
+    List<A> x = this;
+    for (int i = 0; i < length(); i++) {
+      a[i] = x.head();
+      x = x.tail();
+    }
+
+    return Array.array(a);
+  }
+
+  /**
+   * Returns an array from this list.
+   *
+   * @param c The class type of the array to return.
+   * @return An array from this list.
+   */
+  public final A[] array(final Class<A[]> c) {
+    return toArray(c).array(c);
+  }
+
+  /**
+   * Prepends (cons) the given element to this list to product a new list.
+   *
+   * @param a The element to prepend.
+   * @return A new list with the given element at the head.
+   */
+  public final List<A> cons(final A a) {
+    return new Cons<A>(a, this);
+  }
+
+  /**
+   * Prepends (cons) the given element to this list to product a new list. This method is added to prevent conflict with
+   * overloads.
+   *
+   * @param a The element to prepend.
+   * @return A new list with the given element at the head.
+   */
+  public final List<A> conss(final A a) {
+    return new Cons<A>(a, this);
+  }
+
+  /**
+   * Maps the given function across this list.
+   *
+   * @param f The function to map across this list.
+   * @return A new list after the given function has been applied to each element.
+   */
+  public final <B> List<B> map(final F<A, B> f) {
+    final Buffer<B> bs = empty();
+
+    for (List<A> xs = this; xs.isNotEmpty(); xs = xs.tail()) {
+      bs.snoc(f.f(xs.head()));
+    }
+
+    return bs.toList();
+  }
+
+  /**
+   * Performs a side-effect for each element of this list.
+   *
+   * @param f The side-effect to perform for the given element.
+   * @return The unit value.
+   */
+  public final Unit foreach(final F<A, Unit> f) {
+    for (List<A> xs = this; xs.isNotEmpty(); xs = xs.tail()) {
+      f.f(xs.head());
+    }
+
+    return unit();
+  }
+
+  /**
+   * Performs a side-effect for each element of this list.
+   *
+   * @param f The side-effect to perform for the given element.
+   */
+  public final void foreachDoEffect(final Effect1<A> f) {
+    for (List<A> xs = this; xs.isNotEmpty(); xs = xs.tail()) {
+      f.f(xs.head());
+    }
+  }
+
+  /**
+   * Filters elements from this list by returning only elements which produce <code>true</code> when
+   * the given function is applied to them.
+   *
+   * @param f The predicate function to filter on.
+   * @return A new list whose elements all match the given predicate.
+   */
+  public final List<A> filter(final F<A, Boolean> f) {
+    final Buffer<A> b = empty();
+
+    for (List<A> xs = this; xs.isNotEmpty(); xs = xs.tail()) {
+      final A h = xs.head();
+      if (f.f(h)) {
+        b.snoc(h);
+      }
+    }
+
+    return b.toList();
+  }
+
+  /**
+   * Filters elements from this list by returning only elements which produce <code>false</code> when
+   * the given function is applied to them.
+   *
+   * @param f The predicate function to filter on.
+   * @return A new list whose elements do not match the given predicate.
+   */
+  public final List<A> removeAll(final F<A, Boolean> f) {
+    return filter(compose(not, f));
+  }
+
+  /**
+   * Removes the first element that equals the given object.
+   * To remove all matches, use <code>removeAll(e.eq(a))</code>
+   *
+   * @param a The element to remove
+   * @param e An <code>Equals</code> instance for the element's type.
+   * @return A new list whose elements do not match the given predicate.
+   */
+  public final List<A> delete(final A a, final Equal<A> e) {
+    final P2<List<A>, List<A>> p = span(compose(not, e.eq(a)));
+    return p._2().isEmpty() ? p._1() : p._1().append(p._2().tail());
+  }
+
+  /**
+   * Returns the first elements of the head of this list that match the given predicate function.
+   *
+   * @param f The predicate function to apply on this list until it finds an element that does not
+   *          hold, or the list is exhausted.
+   * @return The first elements of the head of this list that match the given predicate function.
+   */
+  public final List<A> takeWhile(final F<A, Boolean> f) {
+    final Buffer<A> b = empty();
+    boolean taking = true;
+
+    for (List<A> xs = this; xs.isNotEmpty() && taking; xs = xs.tail()) {
+      final A h = xs.head();
+      if (f.f(h)) {
+        b.snoc(h);
+      } else {
+        taking = false;
+      }
+    }
+
+    return b.toList();
+  }
+
+  /**
+   * Removes elements from the head of this list that do not match the given predicate function
+   * until an element is found that does match or the list is exhausted.
+   *
+   * @param f The predicate function to apply through this list.
+   * @return The list whose first element does not match the given predicate function.
+   */
+  public final List<A> dropWhile(final F<A, Boolean> f) {
+    List<A> xs;
+
+    //noinspection StatementWithEmptyBody
+    for (xs = this; xs.isNotEmpty() && f.f(xs.head()); xs = xs.tail()) ;
+
+    return xs;
+  }
+
+  /**
+   * Returns a tuple where the first element is the longest prefix of this list that satisfies
+   * the given predicate and the second element is the remainder of the list.
+   *
+   * @param p A predicate to be satisfied by a prefix of this list.
+   * @return A tuple where the first element is the longest prefix of this list that satisfies
+   *         the given predicate and the second element is the remainder of the list.
+   */
+  public final P2<List<A>, List<A>> span(final F<A, Boolean> p) {
+    final Buffer<A> b = empty();
+    for (List<A> xs = this; xs.isNotEmpty(); xs = xs.tail()) {
+      if (p.f(xs.head()))
+        b.snoc(xs.head());
+      else
+        return P.p(b.toList(), xs);
+    }
+    return P.p(b.toList(), List.<A>nil());
+  }
+
+  /**
+   * Returns a tuple where the first element is the longest prefix of this list that does not satisfy
+   * the given predicate and the second element is the remainder of the list.
+   *
+   * @param p A predicate for an element to not satisfy by a prefix of this list.
+   * @return A tuple where the first element is the longest prefix of this list that does not satisfy
+   *         the given predicate and the second element is the remainder of the list.
+   */
+  public final P2<List<A>, List<A>> breakk(final F<A, Boolean> p) {
+    return span(new F<A, Boolean>() {
+      public Boolean f(final A a) {
+        return !p.f(a);
+      }
+    });
+  }
+
+  /**
+   * Groups elements according to the given equality implementation by longest
+   * sequence of equal elements.
+   *
+   * @param e The equality implementation for the elements.
+   * @return A list of grouped elements.
+   */
+  public final List<List<A>> group(final Equal<A> e) {
+    if (isEmpty())
+      return nil();
+    else {
+      final P2<List<A>, List<A>> z = tail().span(e.eq(head()));
+      return cons(z._1().cons(head()), z._2().group(e));
+    }
+  }
+
+
+  /**
+   * Binds the given function across each element of this list with a final join.
+   *
+   * @param f The function to apply to each element of this list.
+   * @return A new list after performing the map, then final join.
+   */
+  public final <B> List<B> bind(final F<A, List<B>> f) {
+    final Buffer<B> b = empty();
+
+    for (List<A> xs = this; xs.isNotEmpty(); xs = xs.tail()) {
+      b.append(f.f(xs.head()));
+    }
+
+    return b.toList();
+  }
+
+  /**
+   * Binds the given function across each element of this list and the given list with a final
+   * join.
+   *
+   * @param lb A given list to bind the given function with.
+   * @param f  The function to apply to each element of this list and the given list.
+   * @return A new list after performing the map, then final join.
+   */
+  public final <B, C> List<C> bind(final List<B> lb, final F<A, F<B, C>> f) {
+    return lb.apply(map(f));
+  }
+
+  /**
+   * Binds the given function across each element of this list and the given list with a final
+   * join.
+   *
+   * @param lb A given list to bind the given function with.
+   * @param f  The function to apply to each element of this list and the given list.
+   * @return A new list after performing the map, then final join.
+   */
+  public final <B, C> List<C> bind(final List<B> lb, final F2<A, B, C> f) {
+    return bind(lb, curry(f));
+  }
+
+  /**
+   * Promotes the given function of arity-2 to a function on lists.
+   *
+   * @param f The function to promote to a function on lists.
+   * @return The given function, promoted to operate on lists.
+   */
+  public static <A, B, C> F<List<A>, F<List<B>, List<C>>> liftM2(final F<A, F<B, C>> f) {
+    return curry(new F2<List<A>, List<B>, List<C>>() {
+      public List<C> f(final List<A> as, final List<B> bs) {
+        return as.bind(bs, f);
+      }
+    });
+  }
+
+  /**
+   * Binds the given function across each element of this list and the given lists with a final
+   * join.
+   *
+   * @param lb A given list to bind the given function with.
+   * @param lc A given list to bind the given function with.
+   * @param f  The function to apply to each element of this list and the given lists.
+   * @return A new list after performing the map, then final join.
+   */
+  public final <B, C, D> List<D> bind(final List<B> lb, final List<C> lc, final F<A, F<B, F<C, D>>> f) {
+    return lc.apply(bind(lb, f));
+  }
+
+  /**
+   * Binds the given function across each element of this list and the given lists with a final
+   * join.
+   *
+   * @param lb A given list to bind the given function with.
+   * @param lc A given list to bind the given function with.
+   * @param ld A given list to bind the given function with.
+   * @param f  The function to apply to each element of this list and the given lists.
+   * @return A new list after performing the map, then final join.
+   */
+  public final <B, C, D, E> List<E> bind(final List<B> lb, final List<C> lc, final List<D> ld,
+                                   final F<A, F<B, F<C, F<D, E>>>> f) {
+    return ld.apply(bind(lb, lc, f));
+  }
+
+  /**
+   * Binds the given function across each element of this list and the given lists with a final
+   * join.
+   *
+   * @param lb A given list to bind the given function with.
+   * @param lc A given list to bind the given function with.
+   * @param ld A given list to bind the given function with.
+   * @param le A given list to bind the given function with.
+   * @param f  The function to apply to each element of this list and the given lists.
+   * @return A new list after performing the map, then final join.
+   */
+  public final <B, C, D, E, F$> List<F$> bind(final List<B> lb, final List<C> lc, final List<D> ld, final List<E> le,
+                                        final F<A, F<B, F<C, F<D, F<E, F$>>>>> f) {
+    return le.apply(bind(lb, lc, ld, f));
+  }
+
+  /**
+   * Binds the given function across each element of this list and the given lists with a final
+   * join.
+   *
+   * @param lb A given list to bind the given function with.
+   * @param lc A given list to bind the given function with.
+   * @param ld A given list to bind the given function with.
+   * @param le A given list to bind the given function with.
+   * @param lf A given list to bind the given function with.
+   * @param f  The function to apply to each element of this list and the given lists.
+   * @return A new list after performing the map, then final join.
+   */
+  public final <B, C, D, E, F$, G> List<G> bind(final List<B> lb, final List<C> lc, final List<D> ld, final List<E> le,
+                                          final List<F$> lf, final F<A, F<B, F<C, F<D, F<E, F<F$, G>>>>>> f) {
+    return lf.apply(bind(lb, lc, ld, le, f));
+  }
+
+  /**
+   * Binds the given function across each element of this list and the given lists with a final
+   * join.
+   *
+   * @param lb A given list to bind the given function with.
+   * @param lc A given list to bind the given function with.
+   * @param ld A given list to bind the given function with.
+   * @param le A given list to bind the given function with.
+   * @param lf A given list to bind the given function with.
+   * @param lg A given list to bind the given function with.
+   * @param f  The function to apply to each element of this list and the given lists.
+   * @return A new list after performing the map, then final join.
+   */
+  public final <B, C, D, E, F$, G, H> List<H> bind(final List<B> lb, final List<C> lc, final List<D> ld, final List<E> le,
+                                             final List<F$> lf, final List<G> lg,
+                                             final F<A, F<B, F<C, F<D, F<E, F<F$, F<G, H>>>>>>> f) {
+    return lg.apply(bind(lb, lc, ld, le, lf, f));
+  }
+
+  /**
+   * Binds the given function across each element of this list and the given lists with a final
+   * join.
+   *
+   * @param lb A given list to bind the given function with.
+   * @param lc A given list to bind the given function with.
+   * @param ld A given list to bind the given function with.
+   * @param le A given list to bind the given function with.
+   * @param lf A given list to bind the given function with.
+   * @param lg A given list to bind the given function with.
+   * @param lh A given list to bind the given function with.
+   * @param f  The function to apply to each element of this list and the given lists.
+   * @return A new list after performing the map, then final join.
+   */
+  public final <B, C, D, E, F$, G, H, I> List<I> bind(final List<B> lb, final List<C> lc, final List<D> ld, final List<E> le,
+                                                final List<F$> lf, final List<G> lg, final List<H> lh,
+                                                final F<A, F<B, F<C, F<D, F<E, F<F$, F<G, F<H, I>>>>>>>> f) {
+    return lh.apply(bind(lb, lc, ld, le, lf, lg, f));
+  }
+
+  /**
+   * Performs a bind across each list element, but ignores the element value each time.
+   *
+   * @param bs The list to apply in the final join.
+   * @return A new list after the final join.
+   */
+  public final <B> List<B> sequence(final List<B> bs) {
+    final F<A, List<B>> c = constant(bs);
+    return bind(c);
+  }
+
+  /**
+   * Performs function application within a list (applicative functor pattern).
+   *
+   * @param lf The list of functions to apply.
+   * @return A new list after applying the given list of functions through this list.
+   */
+  public final <B> List<B> apply(final List<F<A, B>> lf) {
+    return lf.bind(new F<F<A, B>, List<B>>() {
+      public List<B> f(final F<A, B> f) {
+        return map(f);
+      }
+    });
+  }
+
+  /**
+   * Appends the given list to this list.
+   *
+   * @param as The list to append to this one.
+   * @return A new list that has appended the given list.
+   */
+  public final List<A> append(final List<A> as) {
+    return fromList(this).append(as).toList();
+  }
+
+  /**
+   * Performs a right-fold reduction across this list. This function uses O(length) stack space.
+   *
+   * @param f The function to apply on each element of the list.
+   * @param b The beginning value to start the application from.
+   * @return The final result after the right-fold reduction.
+   */
+  public final <B> B foldRight(final F<A, F<B, B>> f, final B b) {
+    return isEmpty() ? b : f.f(head()).f(tail().foldRight(f, b));
+  }
+
+  /**
+   * Performs a right-fold reduction across this list. This function uses O(length) stack space.
+   *
+   * @param f The function to apply on each element of the list.
+   * @param b The beginning value to start the application from.
+   * @return The final result after the right-fold reduction.
+   */
+  public final <B> B foldRight(final F2<A, B, B> f, final B b) {
+    return foldRight(curry(f), b);
+  }
+
+  /**
+   * Performs a right-fold reduction across this list in O(1) stack space.
+   * @param f The function to apply on each element of the list.
+   * @param b The beginning value to start the application from.
+   * @return A Trampoline containing the final result after the right-fold reduction.
+   */
+  public final <B> Trampoline<B> foldRightC(final F2<A, B, B> f, final B b) {
+    return Trampoline.suspend(new P1<Trampoline<B>>() {
+      public Trampoline<B> _1() {
+        return isEmpty() ? Trampoline.pure(b) : tail().foldRightC(f, b).map(F2Functions.f(f, head()));
+      }
+    });
+  }
+
+  /**
+   * Performs a left-fold reduction across this list. This function runs in constant space.
+   *
+   * @param f The function to apply on each element of the list.
+   * @param b The beginning value to start the application from.
+   * @return The final result after the left-fold reduction.
+   */
+  public final <B> B foldLeft(final F<B, F<A, B>> f, final B b) {
+    B x = b;
+
+    for (List<A> xs = this; !xs.isEmpty(); xs = xs.tail()) {
+      x = f.f(x).f(xs.head());
+    }
+
+    return x;
+  }
+
+  /**
+   * Performs a left-fold reduction across this list. This function runs in constant space.
+   *
+   * @param f The function to apply on each element of the list.
+   * @param b The beginning value to start the application from.
+   * @return The final result after the left-fold reduction.
+   */
+  public final <B> B foldLeft(final F2<B, A, B> f, final B b) {
+    return foldLeft(curry(f), b);
+  }
+
+  /**
+   * Takes the first 2 elements of the list and applies the function to them,
+   * then applies the function to the result and the third element and so on.
+   *
+   * @param f The function to apply on each element of the list.
+   * @return The final result after the left-fold reduction.
+   */
+  public final A foldLeft1(final F2<A, A, A> f) {
+    return foldLeft1(curry(f));
+  }
+
+  /**
+   * Takes the first 2 elements of the list and applies the function to them,
+   * then applies the function to the result and the third element and so on.
+   *
+   * @param f The function to apply on each element of the list.
+   * @return The final result after the left-fold reduction.
+   */
+  public final A foldLeft1(final F<A, F<A, A>> f) {
+    if (isEmpty())
+      throw error("Undefined: foldLeft1 on empty list");
+    return tail().foldLeft(f, head());
+  }
+
+  /**
+   * Reverse this list in constant stack space.
+   *
+   * @return A new list that is the reverse of this one.
+   */
+  public final List<A> reverse() {
+    return foldLeft(new F<List<A>, F<A, List<A>>>() {
+      public F<A, List<A>> f(final List<A> as) {
+        return new F<A, List<A>>() {
+          public List<A> f(final A a) {
+            return cons(a, as);
+          }
+        };
+      }
+    }, List.<A>nil());
+  }
+
+  /**
+   * Returns the element at the given index if it exists, fails otherwise.
+   *
+   * @param i The index at which to get the element to return.
+   * @return The element at the given index if it exists, fails otherwise.
+   */
+  public final A index(final int i) {
+    if (i < 0 || i > length() - 1)
+      throw error("index " + i + " out of range on list with length " + length());
+    else {
+      List<A> xs = this;
+
+      for (int c = 0; c < i; c++) {
+        xs = xs.tail();
+      }
+
+      return xs.head();
+    }
+  }
+
+  /**
+   * Takes the given number of elements from the head of this list if they are available.
+   *
+   * @param i The maximum number of elements to take from this list.
+   * @return A new list with a length the same, or less than, this list.
+   */
+  public final List<A> take(final int i) {
+    return i <= 0 || isEmpty() ? List.<A>nil() : cons(head(), tail().take(i - 1));
+  }
+
+  /**
+   * Drops the given number of elements from the head of this list if they are available.
+   *
+   * @param i The number of elements to drop from the head of this list.
+   * @return A list with a length the same, or less than, this list.
+   */
+  public final List<A> drop(final int i) {
+    int c = 0;
+
+    List<A> xs = this;
+
+    for (; xs.isNotEmpty() && c < i; xs = xs.tail())
+      c++;
+
+    return xs;
+  }
+
+  /**
+   * Splits this list into two lists at the given index. If the index goes out of bounds, then it is
+   * normalised so that this function never fails.
+   *
+   * @param i The index at which to split this list in two parts.
+   * @return A pair of lists split at the given index of this list.
+   */
+  public final P2<List<A>, List<A>> splitAt(final int i) {
+    P2<List<A>, List<A>> s = p(List.<A>nil(), List.<A>nil());
+
+    int c = 0;
+    for (List<A> xs = this; xs.isNotEmpty(); xs = xs.tail()) {
+      final A h = xs.head();
+      s = c < i ? s.map1(new F<List<A>, List<A>>() {
+        public List<A> f(final List<A> as) {
+          return as.snoc(h);
+        }
+      }) : s.map2(new F<List<A>, List<A>>() {
+        public List<A> f(final List<A> as) {
+          return as.snoc(h);
+        }
+      });
+      c++;
+    }
+
+    return s;
+  }
+
+  /**
+   * Splits this list into lists of the given size. If the size of this list is not evenly divisible by
+   * the given number, the last partition will contain the remainder.
+   *
+   * @param n The size of the partitions into which to split this list.
+   * @return A list of sublists of this list, of at most the given size.
+   */
+  public final List<List<A>> partition(final int n) {
+    if (n < 1)
+      throw error("Can't create list partitions shorter than 1 element long.");
+    if (isEmpty())
+      throw error("Partition on empty list.");
+    return unfold(new F<List<A>, Option<P2<List<A>, List<A>>>>() {
+      public Option<P2<List<A>, List<A>>> f(final List<A> as) {
+        return as.isEmpty() ? Option.<P2<List<A>, List<A>>>none() : some(as.splitAt(n));
+      }
+    }, this);
+  }
+
+  /**
+   * Returns the list of initial segments of this list, shortest first.
+   *
+   * @return The list of initial segments of this list, shortest first.
+   */
+  public final List<List<A>> inits() {
+    List<List<A>> s = single(List.<A>nil());
+    if (isNotEmpty())
+      s = s.append(tail().inits().map(List.<A>cons().f(head())));
+    return s;
+  }
+
+  /**
+   * Returns the list of final segments of this list, longest first.
+   *
+   * @return The list of final segments of this list, longest first.
+   */
+  public final List<List<A>> tails() {
+    return isEmpty() ? single(List.<A>nil()) : cons(this, tail().tails());
+  }
+
+  /**
+   * Sorts this list using the given order over elements using a <em>merge sort</em> algorithm.
+   *
+   * @param o The order over the elements of this list.
+   * @return A sorted list according to the given order.
+   */
+  public final List<A> sort(final Ord<A> o) {
+    if (isEmpty())
+      return nil();
+    else if (tail().isEmpty())
+      return this;
+    else {
+      final class Merge<A> {
+        List<A> merge(List<A> xs, List<A> ys, final Ord<A> o) {
+          final Buffer<A> buf = empty();
+
+          while (true) {
+            if (xs.isEmpty()) {
+              buf.append(ys);
+              break;
+            }
+
+            if (ys.isEmpty()) {
+              buf.append(xs);
+              break;
+            }
+
+            final A x = xs.head();
+            final A y = ys.head();
+
+            if (o.isLessThan(x, y)) {
+              buf.snoc(x);
+              xs = xs.tail();
+            } else {
+              buf.snoc(y);
+              ys = ys.tail();
+            }
+          }
+
+          return buf.toList();
+        }
+      }
+
+      final P2<List<A>, List<A>> s = splitAt(length() / 2);
+      return new Merge<A>().merge(s._1().sort(o), s._2().sort(o), o);
+    }
+  }
+
+  /**
+   * Zips this list with the given list using the given function to produce a new list. If this list
+   * and the given list have different lengths, then the longer list is normalised so this function
+   * never fails.
+   *
+   * @param bs The list to zip this list with.
+   * @param f  The function to zip this list and the given list with.
+   * @return A new list with a length the same as the shortest of this list and the given list.
+   */
+  public final <B, C> List<C> zipWith(List<B> bs, final F<A, F<B, C>> f) {
+    final Buffer<C> buf = empty();
+    List<A> as = this;
+
+    while (as.isNotEmpty() && bs.isNotEmpty()) {
+      buf.snoc(f.f(as.head()).f(bs.head()));
+      as = as.tail();
+      bs = bs.tail();
+    }
+
+    return buf.toList();
+  }
+
+  /**
+   * Zips this list with the given list using the given function to produce a new list. If this list
+   * and the given list have different lengths, then the longer list is normalised so this function
+   * never fails.
+   *
+   * @param bs The list to zip this list with.
+   * @param f  The function to zip this list and the given list with.
+   * @return A new list with a length the same as the shortest of this list and the given list.
+   */
+  public final <B, C> List<C> zipWith(final List<B> bs, final F2<A, B, C> f) {
+    return zipWith(bs, curry(f));
+  }
+
+  /**
+   * Provides a first-class version of zipWith
+   *
+   * @return The first-class version of zipWith
+   */
+  public static <A, B, C> F<List<A>, F<List<B>, F<F<A, F<B, C>>, List<C>>>> zipWith() {
+    return curry(new F3<List<A>, List<B>, F<A, F<B, C>>, List<C>>() {
+      public List<C> f(final List<A> as, final List<B> bs, final F<A, F<B, C>> f) {
+        return as.zipWith(bs, f);
+      }
+    });
+  }
+
+  /**
+   * Zips this list with the given list to produce a list of pairs. If this list and the given list
+   * have different lengths, then the longer list is normalised so this function never fails.
+   *
+   * @param bs The list to zip this list with.
+   * @return A new list with a length the same as the shortest of this list and the given list.
+   */
+  public final <B> List<P2<A, B>> zip(final List<B> bs) {
+    final F<A, F<B, P2<A, B>>> __2 = p2();
+    return zipWith(bs, __2);
+  }
+
+  /**
+   * The first-class version of the zip function.
+   *
+   * @return A function that zips the given lists to produce a list of pairs.
+   */
+  public static <A, B> F<List<A>, F<List<B>, List<P2<A, B>>>> zip() {
+    return curry(new F2<List<A>, List<B>, List<P2<A, B>>>() {
+      public List<P2<A, B>> f(final List<A> as, final List<B> bs) {
+        return as.zip(bs);
+      }
+    });
+  }
+
+  /**
+   * Zips this list with the index of its element as a pair.
+   *
+   * @return A new list with the same length as this list.
+   */
+  public final List<P2<A, Integer>> zipIndex() {
+    return zipWith(range(0, length()), new F<A, F<Integer, P2<A, Integer>>>() {
+      public F<Integer, P2<A, Integer>> f(final A a) {
+        return new F<Integer, P2<A, Integer>>() {
+          public P2<A, Integer> f(final Integer i) {
+            return p(a, i);
+          }
+        };
+      }
+    });
+  }
+
+  /**
+   * Appends (snoc) the given element to this list to produce a new list.
+   *
+   * @param a The element to append to this list.
+   * @return A new list with the given element appended.
+   */
+  public final List<A> snoc(final A a) {
+    return fromList(this).snoc(a).toList();
+  }
+
+  /**
+   * Returns <code>true</code> if the predicate holds for all of the elements of this list,
+   * <code>false</code> otherwise (<code>true</code> for the empty list).
+   *
+   * @param f The predicate function to test on each element of this list.
+   * @return <code>true</code> if the predicate holds for all of the elements of this list,
+   *         <code>false</code> otherwise.
+   */
+  public final boolean forall(final F<A, Boolean> f) {
+    return isEmpty() || f.f(head()) && tail().forall(f);
+  }
+
+  /**
+   * Returns <code>true</code> if the predicate holds for at least one of the elements of this list,
+   * <code>false</code> otherwise (<code>false</code> for the empty list).
+   *
+   * @param f The predicate function to test on the elements of this list.
+   * @return <code>true</code> if the predicate holds for at least one of the elements of this
+   *         list.
+   */
+  public final boolean exists(final F<A, Boolean> f) {
+    return find(f).isSome();
+  }
+
+  /**
+   * Finds the first occurrence of an element that matches the given predicate or no value if no
+   * elements match.
+   *
+   * @param f The predicate function to test on elements of this list.
+   * @return The first occurrence of an element that matches the given predicate or no value if no
+   *         elements match.
+   */
+  public final Option<A> find(final F<A, Boolean> f) {
+    for (List<A> as = this; as.isNotEmpty(); as = as.tail()) {
+      if (f.f(as.head()))
+        return some(as.head());
+    }
+
+    return none();
+  }
+
+  /**
+   * Intersperses the given argument between each element of this list.
+   *
+   * @param a The separator to intersperse in this list.
+   * @return A list with the given separator interspersed.
+   */
+  public final List<A> intersperse(final A a) {
+    return isEmpty() || tail().isEmpty() ?
+           this :
+           cons(head(), cons(a, tail().intersperse(a)));
+  }
+
+  /**
+   * Intersperses this list through the given list then joins the results.
+   *
+   * @param as The list to intersperse through.
+   * @return This list through the given list then joins the results.
+   */
+  @SuppressWarnings({"unchecked"})
+  public final List<A> intercalate(final List<List<A>> as) {
+    return join(as.intersperse(this));
+  }
+
+  /**
+   * Removes duplicates according to object equality.
+   *
+   * @return A list without duplicates according to object equality.
+   */
+  public final List<A> nub() {
+    return nub(Equal.<A>anyEqual());
+  }
+
+  /**
+   * Removes duplicates according to the given equality. Warning: O(n^2).
+   *
+   * @param eq Equality over the elements.
+   * @return A list without duplicates.
+   */
+  public final List<A> nub(final Equal<A> eq) {
+    return isEmpty() ? this : cons(head(), tail().filter(new F<A, Boolean>() {
+      public Boolean f(final A a) {
+        return !eq.eq(a, head());
+      }
+    }).nub(eq));
+  }
+
+  /**
+   * Removes duplicates according to the given ordering. This function is O(n).
+   *
+   * @param o An ordering for the elements.
+   * @return A list without duplicates.
+   */
+  @SuppressWarnings({"unchecked"})
+  public final List<A> nub(final Ord<A> o) {
+    return sort(o).group(o.equal()).map(List.<A>head_());
+  }
+
+  /**
+   * First-class head function.
+   *
+   * @return A function that gets the head of a given list.
+   */
+  public static <A> F<List<A>, A> head_() {
+    return new F<List<A>, A>() {
+      public A f(final List<A> list) {
+        return list.head();
+      }
+    };
+  }
+
+  /**
+   * First-class tail function.
+   *
+   * @return A function that gets the tail of a given list.
+   */
+  public static <A> F<List<A>, List<A>> tail_() {
+    return new F<List<A>, List<A>>() {
+      public List<A> f(final List<A> list) {
+        return list.tail();
+      }
+    };
+  }
+
+  /**
+   * Returns a new list of all the items in this list that do not appear in the given list.
+   *
+   * @param eq an equality for the items of the lists.
+   * @param xs a list to subtract from this list.
+   * @return a list of all the items in this list that do not appear in the given list.
+   */
+  public final List<A> minus(final Equal<A> eq, final List<A> xs) {
+    return removeAll(compose(Monoid.disjunctionMonoid.sumLeft(), xs.mapM(curry(eq.eq()))));
+  }
+
+  /**
+   * Maps the given function of arity-2 across this list and returns a function that applies all the resulting
+   * functions to a given argument.
+   *
+   * @param f A function of arity-2
+   * @return A function that, when given an argument, applies the given function to that argument and every element
+   *         in this list.
+   */
+  public final <B, C> F<B, List<C>> mapM(final F<A, F<B, C>> f) {
+    return sequence_(map(f));
+  }
+
+  /**
+   * Maps the given function across this list by binding through the Option monad.
+   *
+   * @param f The function to apply through the this list.
+   * @return A possible list of values after binding through the Option monad.
+   */
+  public final <B> Option<List<B>> mapMOption(final F<A, Option<B>> f) {
+    return foldRight(new F2<A, Option<List<B>>, Option<List<B>>>() {
+      public Option<List<B>> f(final A a, final Option<List<B>> bs) {
+        return f.f(a).bind(new F<B, Option<List<B>>>() {
+          public Option<List<B>> f(final B b) {
+            return bs.map(new F<List<B>, List<B>>() {
+              public List<B> f(final List<B> bbs) {
+                return bbs.cons(b);
+              }
+            });
+          }
+        });
+      }
+    }, Option.<List<B>>some(List.<B>nil()));
+  }
+
+  /**
+   * Maps the given function across this list by binding through the Trampoline monad.
+   *
+   * @param f The function to apply through the this list.
+   * @return A list of values in the Trampoline monad.
+   */
+  public final <B> Trampoline<List<B>> mapMTrampoline(final F<A, Trampoline<B>> f) {
+    return foldRight(new F2<A, Trampoline<List<B>>, Trampoline<List<B>>>() {
+      public Trampoline<List<B>> f(final A a, final Trampoline<List<B>> bs) {
+        return f.f(a).bind(new F<B, Trampoline<List<B>>>() {
+          public Trampoline<List<B>> f(final B b) {
+            return bs.map(new F<List<B>, List<B>>() {
+              public List<B> f(final List<B> bbs) {
+                return bbs.cons(b);
+              }
+            });
+          }
+        });
+      }
+    }, Trampoline.<List<B>>pure(List.<B>nil()));
+  }
+
+  /**
+   * Returns the index of the first element in this list which is equal (by the given equality) to the
+   * query element, or None if there is no such element.
+   *
+   * @param e An equality for this list's elements.
+   * @param a A query element.
+   * @return The index of the first element in this list which is equal (by the given equality) to the
+   *         query element, or None if there is no such element.
+   */
+  public final Option<Integer> elementIndex(final Equal<A> e, final A a) {
+    return lookup(e, zipIndex(), a);
+  }
+
+  /**
+   * Returns the last element of this list. Undefined for the empty list.
+   *
+   * @return The last element of this list or throws an error if this list is empty.
+   */
+  public final A last() {
+    A a = head();
+    for (List<A> xs = tail(); xs.isNotEmpty(); xs = xs.tail())
+      a = xs.head();
+    return a;
+  }
+
+  /**
+   * Returns all but the last element of this list. Undefiend for the empty list.
+   *
+   * @return All but the last element of this list. Undefiend for the empty list.
+   */
+  public final List<A> init() {
+    List<A> ys = this;
+    final Buffer<A> a = empty();
+    while(ys.isNotEmpty() && ys.tail().isNotEmpty()) {
+      a.snoc(head());
+      ys = ys.tail();
+    }
+    return a.toList();
+  }
+
+  /**
+   * Inserts the given element before the first element that is greater than or equal to it according
+   * to the given ordering.
+   *
+   * @param f An ordering function to compare elements.
+   * @param x The element to insert.
+   * @return A new list with the given element inserted before the first element that is greater than or equal to
+   *         it according to the given ordering.
+   */
+  public final List<A> insertBy(final F<A, F<A, Ordering>> f, final A x) {
+    List<A> ys = this;
+    Buffer<A> xs = empty();
+    while (ys.isNotEmpty() && f.f(x).f(ys.head()) == GT) {
+      xs = xs.snoc(ys.head());
+      ys = ys.tail();
+    }
+    return xs.append(ys.cons(x)).toList();
+  }
+
+  /**
+   * Returns the most common element in this list.
+   *
+   * @param o An ordering for the elements of the list.
+   * @return The most common element in this list.
+   */
+  public final A mode(final Ord<A> o) {
+    return sort(o).group(o.equal()).maximum(intOrd.comap(List.<A>length_())).head();
+  }
+
+  /**
+   * Groups the elements of this list by a given keyFunction into a {@link TreeMap}.
+   * The ordering of the keys is determined by {@link fj.Ord#hashOrd()}.
+   *
+   * @param keyFunction The function to select the keys for the map.
+   * @return A TreeMap containing the keys with the accumulated list of matched elements.
+   */
+  public final <B> TreeMap<B, List<A>> groupBy(final F<A, B> keyFunction) {
+    return groupBy(keyFunction, Ord.hashOrd());
+  }
+
+  /**
+   * Groups the elements of this list by a given keyFunction into a {@link TreeMap}.
+   *
+   * @param keyFunction The function to select the keys for the map.
+   * @param keyOrd An order for the keys of the tree map.
+   * @return A TreeMap containing the keys with the accumulated list of matched elements.
+   */
+  public final <B> TreeMap<B, List<A>> groupBy(final F<A, B> keyFunction, final Ord<B> keyOrd) {
+    return groupBy(keyFunction, Function.identity(), keyOrd);
+  }
+
+  /**
+   * Groups the elements of this list by a given keyFunction into a {@link TreeMap} and transforms
+   * the matching elements with the given valueFunction. The ordering of the keys is determined by
+   * {@link fj.Ord#hashOrd()}.
+   *
+   * @param keyFunction The function to select the keys for the map.
+   * @param valueFunction The function to apply on each matching value.
+   * @return A TreeMap containing the keys with the accumulated list of matched and mapped elements.
+   */
+  public final <B, C> TreeMap<B, List<C>> groupBy(
+      final F<A, B> keyFunction,
+      final F<A, C> valueFunction) {
+    return this.groupBy(keyFunction, valueFunction, Ord.hashOrd());
+  }
+
+  /**
+   * Groups the elements of this list by a given keyFunction into a {@link TreeMap} and transforms
+   * the matching elements with the given valueFunction. The ordering of the keys is determined by
+   * the keyOrd parameter.
+   *
+   * @param keyFunction The function to select the keys for the map.
+   * @param valueFunction The function to apply on each matching value.
+   * @param keyOrd An order for the keys of the tree map.
+   * @return A TreeMap containing the keys with the accumulated list of matched and mapped elements.
+   */
+  public final <B, C> TreeMap<B, List<C>> groupBy(
+      final F<A, B> keyFunction,
+      final F<A, C> valueFunction,
+      final Ord<B> keyOrd) {
+    return this.groupBy(keyFunction, valueFunction, List.<C>nil(), List::cons, keyOrd);
+  }
+
+  /**
+   * Groups the elements of this list by a given keyFunction into a {@link TreeMap} and transforms
+   * the matching elements with the given valueFunction. The ordering of the keys is determined by
+   * the keyOrd parameter.
+   *
+   * @param keyFunction The function to select the keys for the map.
+   * @param valueFunction The function to apply on each matching value.
+   * @param monoid A monoid, which defines the accumulator for the values and the zero value.
+   * @param keyOrd An order for the keys of the tree map.
+   * @return A TreeMap containing the keys with the accumulated list of matched and mapped elements.
+   */
+  public final <B, C> TreeMap<B, C> groupBy(
+      final F<A, B> keyFunction,
+      final F<A, C> valueFunction,
+      final Monoid<C> monoid,
+      final Ord<B> keyOrd) {
+    return groupBy(keyFunction, valueFunction, monoid.zero(),
+        Function.uncurryF2(monoid.sum()), keyOrd);
+  }
+
+  /**
+   * Groups the elements of this list by a given keyFunction, applies the valueFunction and
+   * accumulates the mapped values with the given grouping accumulator function on the grouping
+   * identity.
+   *
+   * @param keyFunction The function to select the keys.
+   * @param valueFunction The function to apply on each element.
+   * @param groupingIdentity The identity, or start value, for the grouping.
+   * @param groupingAcc The accumulator to apply on each matching value.
+   * @param keyOrd An order for the keys of the tree map.
+   * @return A TreeMap containing the keys with the accumulated result of matched and mapped
+   * elements.
+   */
+  public final <B, C, D> TreeMap<B, D> groupBy(
+      final F<A, B> keyFunction,
+      final F<A, C> valueFunction,
+      final D groupingIdentity,
+      final F2<C, D, D> groupingAcc,
+      final Ord<B> keyOrd) {
+    return this.foldLeft(map -> element -> {
+          final B key = keyFunction.f(element);
+          final C value = valueFunction.f(element);
+          return map.set(key, map.get(key)
+              .map(existing -> groupingAcc.f(value, existing))
+              .orSome(groupingAcc.f(value, groupingIdentity)));
+        }, TreeMap.<B, D>empty(keyOrd)
+    );
+  }
+
+
+
+  /**
+   * Returns whether or not all elements in the list are equal according to the given equality test.
+   *
+   * @param eq The equality test.
+   * @return Whether or not all elements in the list are equal according to the given equality test.
+   */
+  public boolean allEqual(final Equal<A> eq) {
+    return isEmpty() || tail().isEmpty() || eq.eq(head(), tail().head()) && tail().allEqual(eq);
+  }
+
+  /**
+   * First-class length.
+   *
+   * @return A function that gets the length of a given list.
+   */
+  public static <A> F<List<A>, Integer> length_() {
+    return new F<List<A>, Integer>() {
+      public Integer f(final List<A> a) {
+        return a.length();
+      }
+    };
+  }
+
+  /**
+   * Returns the maximum element in this list according to the given ordering.
+   *
+   * @param o An ordering for the elements of the list.
+   * @return The maximum element in this list according to the given ordering.
+   */
+  public final A maximum(final Ord<A> o) {
+    return foldLeft1(o.max);
+  }
+
+  /**
+   * Returns the minimum element in this list according to the given ordering.
+   *
+   * @param o An ordering for the elements of the list.
+   * @return The minimum element in this list according to the given ordering.
+   */
+  public final A minimum(final Ord<A> o) {
+    return foldLeft1(o.min);
+  }
+
+  /**
+   * Projects an immutable collection of this list.
+   *
+   * @return An immutable collection of this list.
+   */
+  public final Collection<A> toCollection() {
+    return new AbstractCollection<A>() {
+      public Iterator<A> iterator() {
+        return new Iterator<A>() {
+          private List<A> xs = List.this;
+
+          public boolean hasNext() {
+            return xs.isNotEmpty();
+          }
+
+          public A next() {
+            if (xs.isEmpty())
+              throw new NoSuchElementException();
+            else {
+              final A a = xs.head();
+              xs = xs.tail();
+              return a;
+            }
+          }
+
+          public void remove() {
+            throw new UnsupportedOperationException();
+          }
+        };
+      }
+
+      public int size() {
+        return length();
+      }
+    };
+  }
+
+  private static final class Nil<A> extends List<A> {
+    public static final Nil<Object> INSTANCE = new Nil<Object>();
+
+    public A head() {
+      throw error("head on empty list");
+    }
+
+    public List<A> tail() {
+      throw error("tail on empty list");
+    }
+  }
+
+  private static final class Cons<A> extends List<A> {
+    private final A head;
+    private List<A> tail;
+
+    Cons(final A head, final List<A> tail) {
+      this.head = head;
+      this.tail = tail;
+    }
+
+    public A head() {
+      return head;
+    }
+
+    public List<A> tail() {
+      return tail;
+    }
+
+    private void tail(final List<A> tail) {
+      this.tail = tail;
+    }
+  }
+
+  /**
+   * Constructs a list from the given elements.
+   *
+   * @param as The elements to construct a list with.
+   * @return A list with the given elements.
+   */
+  public static <A> List<A> list(final A... as) {
+    return Array.array(as).toList();
+  }
+
+  /**
+   * Returns an empty list.
+   *
+   * @return An empty list.
+   */
+  @SuppressWarnings("unchecked")
+  public static <A> List<A> nil() {
+    return (Nil<A>) Nil.INSTANCE;
+  }
+
+  /**
+   * Returns a function that prepends (cons) an element to a list to produce a new list.
+   *
+   * @return A function that prepends (cons) an element to a list to produce a new list.
+   */
+  public static <A> F<A, F<List<A>, List<A>>> cons() {
+    return new F<A, F<List<A>, List<A>>>() {
+      public F<List<A>, List<A>> f(final A a) {
+        return new F<List<A>, List<A>>() {
+          public List<A> f(final List<A> tail) {
+            return cons(a, tail);
+          }
+        };
+      }
+    };
+  }
+
+  public static <A> F2<A, List<A>, List<A>> cons_() {
+      return (a, listA) -> cons(a, listA);
+  }
+
+  /**
+   * Returns a function that prepends a value to the given list.
+   *
+   * @param tail The list to prepend to.
+   * @return A function that prepends a value to the given list.
+   */
+  public static <A> F<A, List<A>> cons(final List<A> tail) {
+    return new F<A, List<A>>() {
+      public List<A> f(final A a) {
+        return tail.cons(a);
+      }
+    };
+  }
+
+  /**
+   * Returns a function that prepends the given value to a list.
+   *
+   * @param a The value to prepend to a list.
+   * @return A function that prepends the given value to a list.
+   */
+  public static <A> F<List<A>, List<A>> cons_(final A a) {
+    return new F<List<A>, List<A>>() {
+      public List<A> f(final List<A> as) {
+        return as.cons(a);
+      }
+    };
+  }
+
+  /**
+   * Prepends the given head element to the given tail element to produce a new list.
+   *
+   * @param head The element to prepend.
+   * @param tail The list to prepend to.
+   * @return The list with the given element prepended.
+   */
+  public static <A> List<A> cons(final A head, final List<A> tail) {
+    return new Cons<A>(head, tail);
+  }
+
+  /**
+   * Returns a function that determines whether a given list is empty.
+   *
+   * @return A function that determines whether a given list is empty.
+   */
+  public static <A> F<List<A>, Boolean> isEmpty_() {
+    return new F<List<A>, Boolean>() {
+      public Boolean f(final List<A> as) {
+        return as.isEmpty();
+      }
+    };
+  }
+
+  /**
+   * Returns a function that determines whether a given list is not empty.
+   *
+   * @return A function that determines whether a given list is not empty.
+   */
+  public static <A> F<List<A>, Boolean> isNotEmpty_() {
+    return new F<List<A>, Boolean>() {
+      public Boolean f(final List<A> as) {
+        return as.isNotEmpty();
+      }
+    };
+  }
+
+  /**
+   * Joins the given list of lists using a bind operation.
+   *
+   * @param o The list of lists to join.
+   * @return A new list that is the join of the given lists.
+   */
+  public static <A> List<A> join(final List<List<A>> o) {
+    final F<List<A>, List<A>> id = identity();
+    return o.bind(id);
+  }
+
+  /**
+   * A first-class version of join
+   *
+   * @return A function that joins a list of lists using a bind operation.
+   */
+  public static <A> F<List<List<A>>, List<A>> join() {
+    return new F<List<List<A>>, List<A>>() {
+      public List<A> f(final List<List<A>> as) {
+        return join(as);
+      }
+    };
+  }
+
+  /**
+   * Unfolds across the given function starting at the given value to produce a list.
+   *
+   * @param f The function to unfold across.
+   * @param b The start value to begin the unfold.
+   * @return A new list that is a result of unfolding until the function does not produce a value.
+   */
+  public static <A, B> List<A> unfold(final F<B, Option<P2<A, B>>> f, final B b) {
+    Buffer<A> buf = empty();
+    for (Option<P2<A, B>> o = f.f(b); o.isSome(); o = f.f(o.some()._2())) {
+      buf = buf.snoc(o.some()._1());
+    }
+    return buf.toList();
+  }
+
+  /**
+   * Transforms a list of pairs into a list of first components and a list of second components.
+   *
+   * @param xs The list of pairs to transform.sp
+   * @return A list of first components and a list of second components.
+   */
+  public static <A, B> P2<List<A>, List<B>> unzip(final List<P2<A, B>> xs) {
+    Buffer<A> ba = empty();
+    Buffer<B> bb = empty();
+    for (final P2<A, B> p : xs) {
+      ba = ba.snoc(p._1());
+      bb = bb.snoc(p._2());
+    }
+    return P.p(ba.toList(), bb.toList());
+  }
+
+  /**
+   * Returns a list of the given value replicated the given number of times.
+   *
+   * @param n The number of times to replicate the given value.
+   * @param a The value to replicate.
+   * @return A list of the given value replicated the given number of times.
+   */
+  public static <A> List<A> replicate(final int n, final A a) {
+    return n <= 0 ? List.<A>nil() : replicate(n - 1, a).cons(a);
+  }
+
+  /**
+   * Returns a list of integers from the given <code>from</code> value (inclusive) to the given
+   * <code>to</code> value (exclusive).
+   *
+   * @param from The minimum value for the list (inclusive).
+   * @param to   The maximum value for the list (exclusive).
+   * @return A list of integers from the given <code>from</code> value (inclusive) to the given
+   *         <code>to</code> value (exclusive).
+   */
+  public static List<Integer> range(final int from, final int to) {
+    return from >= to ? List.<Integer>nil() : cons(from, range(from + 1, to));
+  }
+
+  /**
+   * Returns a list of characters from the given string. The inverse of this function is {@link
+   * #asString(List)}.
+   *
+   * @param s The string to produce the list of characters from.
+   * @return A list of characters from the given string.
+   */
+  public static List<Character> fromString(final String s) {
+    List<Character> cs = nil();
+
+    for (int i = s.length() - 1; i >= 0; i--)
+      cs = cons(s.charAt(i), cs);
+
+    return cs;
+  }
+
+  /**
+   * A first-class <code>fromString</code>.
+   *
+   * @return A first-class <code>fromString</code>.
+   */
+  public static F<String, List<Character>> fromString() {
+    return new F<String, List<Character>>() {
+      public List<Character> f(final String s) {
+        return fromString(s);
+      }
+    };
+  }
+
+  /**
+   * Returns a string from the given list of characters. The invers of this function is {@link
+   * #fromString(String)}.
+   *
+   * @param cs The list of characters to produce the string from.
+   * @return A string from the given list of characters.
+   */
+  public static String asString(final List<Character> cs) {
+    final StringBuilder sb = new StringBuilder();
+
+    cs.foreach(new F<Character, Unit>() {
+      public Unit f(final Character c) {
+        sb.append(c);
+        return unit();
+      }
+    });
+    return sb.toString();
+  }
+
+  /**
+   * A first-class <code>asString</code>.
+   *
+   * @return A first-class <code>asString</code>.
+   */
+  public static F<List<Character>, String> asString() {
+    return new F<List<Character>, String>() {
+      public String f(final List<Character> cs) {
+        return asString(cs);
+      }
+    };
+  }
+
+  /**
+   * Returns a list of one element containing the given value.
+   *
+   * @param a The value for the head of the returned list.
+   * @return A list of one element containing the given value.
+   */
+  public static <A> List<A> single(final A a) {
+    return cons(a, List.<A>nil());
+  }
+
+  /**
+   * Creates a list where the first item is calculated by applying the function on the third argument,
+   * the second item by applying the function on the previous result and so on.
+   *
+   * @param f The function to iterate with.
+   * @param p The predicate which must be true for the next item in order to continue the iteration.
+   * @param a The input to the first iteration.
+   * @return A list where the first item is calculated by applying the function on the third argument,
+   *         the second item by applying the function on the previous result and so on.
+   */
+  public static <A> List<A> iterateWhile(final F<A, A> f, final F<A, Boolean> p, final A a) {
+    return unfold(
+        new F<A, Option<P2<A, A>>>() {
+          public Option<P2<A, A>> f(final A o) {
+            return Option.iif(new F<P2<A, A>, Boolean>() {
+              public Boolean f(final P2<A, A> p2) {
+                return p.f(o);
+              }
+            }, P.p(o, f.f(o)));
+          }
+        }
+        , a);
+  }
+
+  /**
+   * Returns an associated value with the given key in the list of pairs.
+   *
+   * @param e The test for equality on keys.
+   * @param x The list of pairs to search.
+   * @param a The key value to find the associated value of.
+   * @return An associated value with the given key in the list of pairs.
+   */
+  public static <A, B> Option<B> lookup(final Equal<A> e, final List<P2<A, B>> x, final A a) {
+    return x.find(new F<P2<A, B>, Boolean>() {
+      public Boolean f(final P2<A, B> p) {
+        return e.eq(p._1(), a);
+      }
+    }).map(P2.<A, B>__2());
+  }
+
+  /**
+   * Returns a partially applied version of {@link #lookup(Equal, List, Object)}.
+   *
+   * @param e The test for equality on keys.
+   * @return A partially applied version of {@link #lookup(Equal , List, Object)}.
+   */
+  public static <A, B> F2<List<P2<A, B>>, A, Option<B>> lookup(final Equal<A> e) {
+    return new F2<List<P2<A, B>>, A, Option<B>>() {
+      public Option<B> f(final List<P2<A, B>> x, final A a) {
+        return lookup(e, x, a);
+      }
+    };
+  }
+
+  /**
+   * Provides a first-class version of bind()
+   *
+   * @return The bind function for lists.
+   */
+  public static <A, B> F<F<A, List<B>>, F<List<A>, List<B>>> bind_() {
+    return curry(new F2<F<A, List<B>>, List<A>, List<B>>() {
+      public List<B> f(final F<A, List<B>> f, final List<A> as) {
+        return as.bind(f);
+      }
+    });
+  }
+
+  /**
+   * Provides a first-class version of map()
+   *
+   * @return The map function for lists.
+   */
+  public static <A, B> F<F<A, B>, F<List<A>, List<B>>> map_() {
+    return curry(new F2<F<A, B>, List<A>, List<B>>() {
+      public List<B> f(final F<A, B> f, final List<A> as) {
+        return as.map(f);
+      }
+    });
+  }
+
+  /**
+   * Turn a list of functions into a function returning a list.
+   *
+   * @param fs The list of functions to sequence into a single function that returns a list.
+   * @return A function that, when given an argument, applies all the functions in the given list to it
+   *         and returns a list of the results.
+   */
+  public static <A, B> F<B, List<A>> sequence_(final List<F<B, A>> fs) {
+    return fs.foldRight(Function.<A, List<A>, List<A>, B>lift(List.<A>cons()), Function
+        .<B, List<A>>constant(List.<A>nil()));
+  }
+
+  /**
+   * Provides a first-class version of foldLeft.
+   *
+   * @return The left fold function for lists.
+   */
+  public static <A, B> F<F<B, F<A, B>>, F<B, F<List<A>, B>>> foldLeft() {
+    return curry(new F3<F<B, F<A, B>>, B, List<A>, B>() {
+      public B f(final F<B, F<A, B>> f, final B b, final List<A> as) {
+        return as.foldLeft(f, b);
+      }
+    });
+  }
+
+  /**
+   * Provides a first-class version of take.
+   *
+   * @return First-class version of take.
+   */
+  public static <A> F<Integer, F<List<A>, List<A>>> take() {
+    return curry(new F2<Integer, List<A>, List<A>>() {
+      public List<A> f(final Integer n, final List<A> as) {
+        return as.take(n);
+      }
+    });
+  }
+
+  /**
+   * Takes the given iterable to a list.
+   *
+   * @param i The iterable to take to a list.
+   * @return A list from the given iterable.
+   */
+  public static <A> List<A> iterableList(final Iterable<A> i) {
+    final Buffer<A> bs = empty();
+
+    for (final A a : i)
+      bs.snoc(a);
+
+    return bs.toList();
+  }
+
+
+  /**
+   * A mutable, singly linked list. This structure should be used <em>very</em> sparingly, in favour
+   * of the {@link List immutable singly linked list structure}.
+   */
+  public static final class Buffer<A> implements Iterable<A> {
+    private List<A> start = nil();
+    private Cons<A> tail;
+    private boolean exported;
+
+    /**
+     * Returns an iterator for this buffer. This method exists to permit the use in a <code>for</code>-each loop.
+     *
+     * @return A iterator for this buffer.
+     */
+    public Iterator<A> iterator() {
+      return start.iterator();
+    }
+
+    /**
+     * Appends (snoc) the given element to this buffer to produce a new buffer.
+     *
+     * @param a The element to append to this buffer.
+     * @return A new buffer with the given element appended.
+     */
+    public Buffer<A> snoc(final A a) {
+      if (exported)
+        copy();
+
+      final Cons<A> t = new Cons<A>(a, List.<A>nil());
+
+      if (tail == null)
+        start = t;
+      else
+        tail.tail(t);
+
+      tail = t;
+
+      return this;
+    }
+
+    /**
+     * Appends the given buffer to this buffer.
+     *
+     * @param as The buffer to append to this one.
+     * @return A new buffer that has appended the given buffer.
+     */
+    public Buffer<A> append(final List<A> as) {
+      for (List<A> xs = as; xs.isNotEmpty(); xs = xs.tail())
+        snoc(xs.head());
+
+      return this;
+    }
+
+    /**
+     * Returns an immutable list projection of this buffer. Modifications to the underlying buffer
+     * will <em>not</em> be reflected in returned lists.
+     *
+     * @return An immutable list projection of this buffer.
+     */
+    public List<A> toList() {
+      exported = !start.isEmpty();
+      return start;
+    }
+
+    /**
+     * Projects an immutable collection of this buffer.
+     *
+     * @return An immutable collection of this buffer.
+     */
+    public Collection<A> toCollection() {
+      return start.toCollection();
+    }
+
+    /**
+     * An empty buffer.
+     *
+     * @return An empty buffer.
+     */
+    public static <A> Buffer<A> empty() {
+      return new Buffer<A>();
+    }
+
+    /**
+     * Constructs a buffer from the given list.
+     *
+     * @param as The list to construct a buffer with.
+     * @return A buffer from the given list.
+     */
+    public static <A> Buffer<A> fromList(final List<A> as) {
+      final Buffer<A> b = new Buffer<A>();
+
+      for (List<A> xs = as; xs.isNotEmpty(); xs = xs.tail())
+        b.snoc(xs.head());
+
+      return b;
+    }
+
+    /**
+     * Takes the given iterable to a buffer.
+     *
+     * @param i The iterable to take to a buffer.
+     * @return A buffer from the given iterable.
+     */
+    public static <A> Buffer<A> iterableBuffer(final Iterable<A> i) {
+      final Buffer<A> b = empty();
+
+      for (final A a : i)
+        b.snoc(a);
+
+      return b;
+    }
+
+    @SuppressWarnings({"ObjectEquality"})
+    private void copy() {
+      List<A> s = start;
+      final Cons<A> t = tail;
+      start = nil();
+      exported = false;
+      while (s != t) {
+        snoc(s.head());
+        s = s.tail();
+      }
+
+      if (t != null)
+        snoc(t.head());
+    }
+  }
+
+    /**
+     * Perform an equality test on this list which delegates to the .equals() method of the member instances.
+     * This is implemented with Equal.listEqual using the anyEqual rule.
+     *
+     * @param obj the other object to check for equality against.
+     * @return true if this list is equal to the provided argument
+     */
+    //Suppress the warning for cast to <code>List<A></code> because the type is checked in the previous line.
+    @SuppressWarnings({ "unchecked" })
+    @Override public boolean equals( final Object obj ) {
+        if ( obj == null || !( obj instanceof List ) ) { return false; }
+
+        //Casting to List<A> here does not cause a runtime exception even if the type arguments don't match.
+        //The cast is done to avoid the compiler warning "raw use of parameterized class 'List'"
+        return Equal.listEqual( Equal.<A>anyEqual() ).eq( this, (List<A>) obj );
+    }
+
+    /**
+     * Compute the hash code from this list as a function of the hash codes of its members.
+     * Delegates to Hash.listHash, using the anyHash() rule, which uses the hash codes of the contents.
+     *
+     * @return the hash code for this list.
+     */
+    @Override public int hashCode() {
+        return Hash.listHash( Hash.<A>anyHash() ).hash( this );
+    }
+
+    /**
+     * Obtain a string representation of this list using the toString implementations of the members.  Uses Show.listShow with F2 argument and may
+     * not be very performant.
+     *
+     * @return a String representation of the list
+     */
+    @Override public String toString() {
+        return Show.listShow( Show.<A>anyShow() ).show( this ).foldLeft( new F2<String, Character, String>() {
+            @Override public String f( final String s, final Character c ) {
+                return s + c;
+            }
+        }, "" );
+    }
+}