Focus is a design element in programming languages that I think deserves more attention than it gets.
A focused language puts emphasis on a set of coherent idioms. Multi-paradigm languages like C++ or C# are unfocused because they lack a certain principle.
Take C, for instance. You can do OOP in C, but it’s awkward. You need structures full of function pointers and the language wasn’t designed for it: it’s not a good idea to do it. The point is that you can but you shouldn’t.
Focus is not so much of what a language has but something that it embodies. A single-paradigm language can still be unfocused, because there can be several ways to wield the singular paradigm. A multi-paradigm language can be focused if the multi-paradigm languages connect at a higher level. Focus can be implemented as a coding standard or it can be something that everybody understands as the idiomatic way of doing things.
Focus is not always a positive trait but it rarely is a negative trait. On the other hand, a lack of focus is more often negative than positive.
Take Haskell, a pure functional language, effectively single-paradigm; it is a very special case. The language itself is absolutely focused to the point of extreme autism, but its flexible type system and vibrant community, there are many ways to program Haskell. Do you absolutely need state? Use state, but be careful. Do you want IO without monads? Well, sure, but be careful.
At a high level, Haskell code is pure. It permits some inconsistencies with its principal paradigm but it eschews them and this is the key difference.
A bigger problem with focus is that it often is intangible. It’s easier to point out languages that are unfocused than those that are. Focus is about philosophy. Some language are very philosophical. For instance, Clojure is just as much about its particular approach to concurrency, state and identity, that is a language implementing those ideas. The language caught on because Rich Hickey, the author, did not market it as the tool that would have solved everybody’s problems, but because he marketed the ideas that Clojure represented as a solution to common programming problems.
“If you want to build a ship, don’t drum up the men to gather wood, divide the work and give orders. Instead, teach them to yearn for the vast and endless sea.”
In this context, Clojure can be seen as a focused language. These core philosophies are what constitute the language, the fact that Clojure happens to be a Lisp dialect implementing the philosophies is secondary in my mind. With that in mind, I acknowledge being a Lisp is also a core part of Clojure, but its principles about state and identity can be implemented in any language. Clojure does let you do OOP but it feels awkward. When you grok Clojure you understand what that means: the language can be bent for that purpose, but it doesn’t want to be. Its philosophy is like a memory-foam, if you tamper with it, it will coalesce back into its original form. When you see that, it’s the moment you understand what Clojure—or any other language—is about.
Some languages double down on philosophy by making it a part of a coding standard and enforcing it: Go. Go embodies simplicity and intuition, intentionally eschewing things that are not modern, but complex, opting to keep the core language simple. Some chalk this down as a negative trait, others love it; I find it to be both good and bad. Good, because I can jump into any Go codebase and get its purpose in minutes; bad, because sometimes I want to use abstractions for which Go is unsuitable. I respect its design philosophy, because it has one, and absolutely flaunts it. It’s not just a structural type system, it’s an idea.
Scala is another beast. It began as an experiment, trying to augment and fix the deficiencies of Java. It was designed by brilliant PLT theorists and the language is a beautiful and magnanimous behemoth. Scala has so many features that it eschews focus either intentionally or unintentionally. On the other hand, Scala is capable of many great things. But if you ask two Scala programmers what Scala represents to them, you may get different answers.
It can be a technical aspect. To some, it might be about Shapeless or all the cool things that go with it. Macros. DSLs. Code generation. Or it could be how Akka or Spark are amazing tools. It could also be a philosophical difference. Some people want an advanced type system and don’t want to be constrained by the laziness and purity of Haskell. Others want the JVM. Some just want a better Java. Some just happen to use it for Spark.
I would choose the simpler Scala, the better Java. Trait-based generics, sum types, implicits, and functional programming, to name a few. This is not just because it’s less complicated, from a business perspective, it makes it easier to hire new programmers.
As a professional Scala developer and a long-time functional programming enthusiast, I fear that I may never comfortably jump to another company, confident that since I’ve written Scala, I can understand their Scala. That, or years of experience, but who knows what’s enough? Their, whoever they may be, Scala might not be the simple Scala I and my colleagues prefer.
This is scary. For the future of the language, this is an untenable position. While I absolutely enjoy working with the language, I’m afraid that it is fated to be like Macbeth from Shakespeare: “thou shalt get kings, though thou be none”. Thus, Scala will inspire a great language and then die. Maybe it already did, and the clock is ticking. Some purport Kotlin as the successor, but I wouldn’t bet on it just yet.
“Ah, but a man’s reach should exceed his grasp, or what’s a heaven for?”
The thing about Scala is that this is a conscious design decision. The language is meant to have everything and the kitchen sink. Programming languages don’t have to be simple. Powerful languages are powerful tools. Use them well, you can achieve greatness. You have to choose your tool set and hone it.
But for Haskell, Go, and Clojure, you’re using them, and you’re thinking, what is the natural way to do this? Once you find it, you find yourself implementing ideas using that philosophy, that natural way, and you’re no longer just using a tool. You’re using an idea.