private <K> FunctionalMultiMap<K, T> groupIntoMap(
final FunctionalMultiMap<K, T> map,
final Function<T, K> groupingFunction,
FunctionalList<T> values) {
return values.isEmpty()
? map
: groupIntoMap(
map.put(groupingFunction.apply(values.head()), values.head()),
groupingFunction,
values.tail());
}
public FunctionalList<T> append(final T element) {
return isEmpty()
? cons(element, FunctionalList.<T>nil())
: cons(head(), tail().append(element));
}
public <U> FunctionalList<U> map(final Function<T, U> mapping) {
return isEmpty() ? FunctionalList.<U>nil() : cons(mapping.apply(head()), tail().map(mapping));
}
private static <T> FunctionalList<T> fromArray(final T[] items, final int start, final int end) {
return start == end
? FunctionalList.<T>nil()
: cons(items[start], fromArray(items, start + 1, end));
}