Sunday, September 8, 2013

An essay about expressiveness, behavior and conciseness in code

This week I came across an interesting tweet, which stated that a code is read more often than it is written.

It can only be true, as any tautology can be. It's like a book, right? Written once, read many... until errata come in the game, or new editions.

That was my point when I replied, by trolling (I admit) that Java is becoming a pain in this area... because of its verbosity.
Hopefully, Nicolas Frankel is clever enough to continue on the discussion tone rather than entering an infinite war where none can win...
So we took the decision to express our point in a cross-referenced blog where you'll find your own way of coding.

Reading a code

Before starting, I would like first to wonder why would we have to read code?

From my point of view, there are several relevant cases:
  • learning a new library, code express more than doc that's why it must be opened
  • improving it by adding new features, in that case, we need to have the big picture before starting any hacks
  • debugging
So what I'll claim based on these three (more? poke me!) cases, is that
  • the two firsts can be eased by a clean code describing a behavior using the right level of conciseness but keeping the expressiveness at its best.
  • the later can be a real pain when the conciseness of the code has been badly chosen

Some words about conciseness and Java

Here I'll brush quickly some additions that Java received over the last couple of versions, a lot involved conciseness.

Let's take List and the for-loop.

See? Everything is about making the code more concise without removing any logic nor features.

However, everything is not that shiny, mostly when you need to add more logic, or let say when one need to enhance the behavior. Can you read the following two examples easily?

Don't know about you, but my feeling is that the behavior is not well represented, and thus we need to touch our in-brain JVM to catch it up.

The problem is that the conciseness introduce at the language level is not flexible enough to express advanced workflow, like early termination or filtering.
Now let's look at a Java 8 version of this example:

The same code, less lines... but is it really the interesting feature? Conciseness? Really!?
I don't think so, the most important part is that the behavior can be catch by combining two simple behaviors:

  • filtering
  • mapping (transforming)
  • limiting (taking)
Another good fact is that using the second version, the behavior can even be easily testable by simply testing the the predicate (dereferenced from the Test class) is returning the right value.
So there is no need to test if an array will be filtered correctly, it's asserted by the library.
Also, the behavior is easily extendable since now the filtering is no more explicitly hardcoded in the behavior -- however we're free to instantiate a specific behavior introducing partially applied method.

Now, it's true that we have to agree on an API and everybody must know it. But I think it's always the case when you're creating an API, you're fixing names and concepts.
The sad fact, in Java, is that they are trying to reinvent the wheel by renaming well know behavior like limit (take), substream (drop + take) in the Collection API. That's why semantic is hard when someone is creating his own taxonomy/ontology of concepts.
Moreover, they took the opportunity to leave some noise, like the stream() call (probably for backward compatibility) which result in a collect method (which is also used to reconstruct a List using a Stream).

Conciseness Expressiveness and Scala

In this section, I won't expand myself into much details about Scala, but I'll just try to show some advantages of the expressiveness that Scala offers... for instance, even implicits (in the call-site) are explicits (in the definition-site).

So I'll just mention two (among many) features brought by Scala which is really missing in Java, both being related to expressing a behavior based on an implicitly available context.

Implicit parameter

In Scala, a method/function can have several parameter blocks, like so:
def add(a:Int)(b:Int) = a+b.

Ok, fine, but the very last parameter block can be declared as implicit, this way:
def persist(user:User)(implicit s:DBSession) = ....

What an implicit parameter block of parameters is, is simply a bunch of parameter that the compiler should be able to find within the compilation stack. And if it can find, in a deterministic way, such parameters they'll be automatically provided at the call-site. An example?
What has just happened there? It's rather simple, when the compiler will fall on the persist call, it'll see that the last block is implicit and not provided so it'll search in the actual scope if there is an object matching the required type. In this case, it finds session.

Again, I don't know about you, but I prefer this at what Hibernate (for instance) does... which is declaring by injection by something using an annotation or what not a session somewhere. And if something goes wrong? I hope you have integration tests, because it'll be check @runtime.
In this case, the compiler will blow out if it cannot find a session object, that's it!

So it's explicit at one single place, and will be implicit at all call sites. And I think it's cool/powerful to have such duality.


A for-comprehension in Scala is very similar to a for loop in Java when dealing with sequences, however it's more than this. But beofre going futher, here is what is possible using lists:

For those of you having already tried to use the Future API of Java should just find the following really pleasant because it'll be terse and straightforward to chain futures, without pain but with some implicit meanings...

What's going on there? We fetched a user in a future, when it has been fetched we fetched each friend, one by one, within a sequence then we yielded both results in a tuple.
The resulting fut variable is yet another Future that will hold this later tuple if all the fetches successfully returned, otherwise everything fails!
Afterwards, it's still allowed to adapt the contained tuple as a new tuple... Note that we're not dealing with the value yet, we're just describing what has to be done when the result will happen... or not.

I'm not enough courageous to write the code using the Future API in Java, it would be too painful for me, too many brain gymnastic for nothing... and I didn't even talked about the number of  bugs It'd be prone of.

Oh yes, one last thing on this for-comprehension, fetch should have an implicit parameter, the storage session/metadata access and the Futures need an ExecutionContext instance to be executable... but it's not the role of this piece of code to create or even pass them!

Flaws of conciseness in Scala

Mainly the flaws are raising when the code tries to be concise at a such level the the expressiveness itself is penalized. 
For instance, sometimes, I like to tweet implementation in 140 characters like this one; this is just fun to do... I won't expect to have such code dropped as is in a project unless there are a lot of reasons (I can't even image a single one).

Why? Because it breaks all good conventions that are becoming the de facto best practices in Scala. For those interested in, there is a very good keynote by Martin Odersky on that.

The most important is probably to track the status of the types chain by decomposing a multicalls line in several ones, the very next one being to not overuse the wildcard underscore for inline function.

So the code in the tweet can be migrated this way from:


What you only need to understand are these 5 concepts:
  1. map
  2. flatMap
  3. groupBy
  4. mapValues
  5. flatten
Which one couldn't you guess correctly? Make a guess than look at these rough and limited explained behaviors:
  1. List<A> => List<B> OR Map<K,V> => Map<L,W>
  2. List<List<A>>  => List<A>
  3. List<A> => Map<K,List<A>>
  4. Map<k,V> => Map<K,W>
  5. List<List<A>> => List<A> OR List<Map<K,V>> => Map<K,V>
I kept it cryptic on purpose because it has been explained so many times on the web!!

But also not that the readable code (that could even be more readable by still using non-verbose tools) is, with comments, less than 2 times taller. But it would require hundreds of line of Java, which I don't even have the energy to write... Or you need to convince me that I should...

Last note: just don't override, nor create operators that haven't a widely known semantic. Haskell is a bad example, even if this language is awesome!