code: public long sum
              (final Collection<Long> c)
          {
          final F2<Long,Long,Long> f = new F2<Long,Long,Long> ()
              {
              public Long run
                      (final Long x,
                       final Long y)
                  {
                  return x + y;
                  }
              };
              
          return foldl (f, 0L, c);
          }
docs: {@inheritDoc}