Solving http://projecteuler.net/index.php?section=problems&id=1 being as functional as possible using Google Guava

guava-functional.java

    static int solution(int limit){
        ImmutableSet<Integer> numbers = intRange(1,limit);
        return foldInsByAdding(Iterables.filter(numbers, dividableByThreeOrFive()));
    }

    private static Predicate<Integer> dividableByThreeOrFive(){
        return new Predicate<Integer>() {
            @Override
            public boolean apply(Integer i){
                return (i % 3 == 0) || (i % 5 == 0); 
            }
        };
    }
    
    /**
     * I would've liked to have a Iterables.fold(integers, addFunction()), but not in guava yet.
     * There is a fold in functionaljava.org though. 
     */
    private static Integer foldInsByAdding(Iterable<Integer> ints){
        int sum = 0;
        for (Integer i : ints){
            sum = sum + i;
        }
        return sum;
    }
    
    /**
     * Guava does not have a Range thingie yet (but will get one this year).
     */
    private static ImmutableSet<Integer> intRange(int from, int to){
        Set<Integer> set = Sets.newHashSet();
        for(int i = from; i < to ; i++){
            set.add(Integer.valueOf(i));
        }
        return ImmutableSet.copyOf(set);
    }