JAVA

left fold java

# https://apocalisp.wordpress.com/2008/04/22/left-fold-in-java/
# now that there is lambdas in Java it's certainly easier but
# this one should stay with us for it is beautiful!
  
  public static <A, B> A fold(F<A, F<B, A>> f, A z, Iterable<B> xs)
    { A p = z;
      for (B x : xs)
        { p = f.f(p).f(x); }
      return p; }

left fold java

public static String concatenate(List<Character> chars) {
        return chars
                .stream()
                .reduce(new StringBuilder(),
                                StringBuilder::append,
                                StringBuilder::append).toString();
    }