Hacker News Reader

Comment by j-pb | Hacker News Reader

Java has a series of control mechanisms that originate from idiomatic assembly. for, while, if, variables.

In clojure for example you rarely use these low level constructs.

What is simpler to read? Which one is more high-/low-level

  List<Integer> even = new List()
  for(int i = 0; i < 100; i++){
    if((i%2)==0){
      even.add(i);
    }
  }
  return even;

  (filter even? (range 0 100))

View on HN

The GP qualified that this is better with newer JDK versions. For instance, in Java 8 you can do:

    IntStream.range(0, 100).filter(i -> i % 2 == 0);

I find i -> i % 2 == 0), still less readable than even?.

But let's step up the game a bit. Let's produce a sequence of the form [true false false true true true false false false false ...] of exact length 1000.

  (take 1000 (mapcat (fn [i] (repeat i (odd? i))) (range)))

Using the Java 8 'stream' API:

   IntStream.iterate(0,  i -> i + 1)
	.mapToObj( i -> Collections.nCopies(i, i % 2 == 0) )
	.flatMap(Collection::stream)
	.limit(1000)

Generate an infinite series of incrementing numbers, starting from 0, map each to a stream of boolean indicating true/false, flatten that stream of streams, then limit the output.

Nicely done :D! You're the first one to get it right.

Yeah, I'd still argue that the clojure stream api is more readable though ;).

  (->> (range)
       (map #(repeat % (odd? %)))
       (apply concat)
       (take 1000)

The thing is that these additions slowly creep into java, which is great. But you still have to wait for the mercy of the language designers.

Clojure is so flexible that it is possible to bring these things in as libraries, resulting in a very lightweight and stable core, and a very rapidly evolving ecosystem.

Also the persistent data-structures of Clojure make life so much easier. It's basically a language build around persistent maps and arrays.

> Also the persistent data-structures of Clojure make life so much easier. It's basically a language build around persistent maps and arrays.

When programming in Java (which I did for 14 years), I always thought about the little machines I was making and how they interacted. In Clojure, I'm thinking about what shape the data should be and what stack of stencils and folds (as a visual metaphor) I need to get it into that shape.

That is to say, Java is object-oriented, Clojure is data-oriented. So take data-orientation and add easy-mode concurrency and you have something wonderful.

To close standard libs gap, let's assume I have static functions for odd() and take() as well as Java8 stream APIs statically imported. After this, it looks pretty compact and readable:

    take(10, i -> range(0, i)
                    .mapToObj(j -> odd(i))
                    .collect(joining(" ")))
    .collect(joining(" "));

For reference, odd and take will look like this:

    private static String odd(int i) {
        return Boolean.toString(i % 2 != 0);
    }

    private static <T> Stream<T> take(int n, Function<Integer, T> f) {
        return Stream.iterate(1, i -> ++i).map(f).limit(n);
    }

To paraphrase Hickey, "I find German less readable than English; that doesn't mean it's unreadable."

How about this then?

    IntStream.range(0, 100).filter(::even);

Not quite what was asked. The intended outcome is a sequence of length 1000 where the elements are 1 * true, 2 * false, 3 * true, 4 * false and so on.

To compare it with what your code produces.

[true false false true true true false false false false ...]

[true false true false true false true false true false ...]

How much assembly have you done? "for"/"while"/etc are coming out of structured programming.

Yes, but that in turn was inspired by the patterns and idioms in assembly that didn't fuck up your codebase.

Simple conditional forward jumps, if, simple conditional backward jumps, while, and simple conditional backward jumps depending on a variable, for.

Imperative != low level.

Because of the way our current hardware is build, it is actually Imperative <=> low level (ignoring forth for a bit).

Because impressive constructs have a somewhat straightforward compilation path to assembly. Even when GC if involved.

Reply on news.ycombinator.com