Looks decent, but I find it difficult to get excited about. Perhaps I'm not the target audience since I'm very comfortable with Scala (and love what Jetbrains is doing with the Scala IntelliJ plugin).
The world is moving on at a frightening speed when it comes to language design currently, largely thanks to Idris. The idea that some people think "hey, let's pick this language from 1995 and change it slightly" is going to cut it ... that's just mind-boggling.
All those new ideas in language design, are exactly that: new and unproven (like the Hindley-Milner type system, which, while quite old already, has not been proven to be a major strength, and it is certainly complicated, esp. its undecipherable error messages).
"Languages from 1995" (I don't know why you picked that specific year; some very successful languages are much, much older) have been used to build really good software, while "new" languages (Heskell, 1990; OCaml, 1996; Scala, 2003) have not proven to completely change software quality in a way just justifies their arguably less intuitive (if only culturally) designs.
Where are all the bug-free Haskell operating systems, drivers and embedded controllers? Where are the OCaml scalable severs? Where are all the Scala complex enterprise apps? I'm not saying there isn't any really good software written in those languages, but not nearly enough to prove a significant qualitative advantage.
On the other hand, when Java came out in 1995, it took maybe 5 years for pretty much the entire software world to adopt it, and it wasn't just marketing: its advantages were palpable and immediately apparent. I think (though I'm not sure), that C and later C++'s adoption was about as fast. If 25 year old languages like Haskell, and even 10 year-old languages like Scala, haven't shown such an immediate and enthusiastic widespread adoption, maybe their advantages aren't that extreme. Instead of those languages' designers sitting mind-boggled, maybe they should think long and hard about what it is that they're solving exactly and how important it really is.
I think the problems tackled by more "modern" languages are either not important enough, or their solution is far from optimal. For example, it is quite possible that a good type system could help produce good software faster (though it isn't certain either), but that this type system is Hindley-Milner seems unlikely at this point. Pluggable type systems (like the ones recently introduced to that 1995 language, and, I believe, also supported by Kotlin) might actually be a better way to go forward. I also think that some more important advances in programming languages have come not from PL researchers, but from developers (Java, Erlang, Clojure).
Haskell advantages are so extreme they elude most.
What were Java first 5 years advantages ? Wasn't it all 'Java is client-side silver bullet' ?
ps: by Pluggable Types did you mean Type Annotation http://openjdk.java.net/projects/type-annotations/ or just the Checker Framework ? http://types.cs.washington.edu/jsr308/
http://docs.oracle.com/javase/tutorial/java/annotations/type...
EDIT: I think Java's initial advantages were taking good C++ concepts, simplifying them, and running in a safe environment (GC memory, app can't just crash etc.).
The most important innovation in the Hindley-Milner type system was parametric polymorphism, since that is the thing that enables you to build more powerful abstractions. Since the release of Java 1.5 and C# 2.0 that is now fully mainstream, but it took more than 25 years.
Any number of companies are still using C++, which itself took decades to reach the level of popularity that it did; Java is the exception rather than the rule in that regard. (And if we're just comparing popularity, I don't know how it is in your corner of the industry, but Scala growth has been massive over the last few years where I've been looking - and that's not based on Sun's marketing millions, but on word of mouth from people who're using it and finding that it helps them write better programs)
I'd argue that it's lambdas, traits (both now in Java 8), and reduced boilerplate for Java beans; also, maybe pattern matching. Now, all of those features are in Kotlin, which has a far simpler (though less expressive, even though that hasn't been proven to be a major problem) type system and much, much smoother integration with Java.
If you spent a few minutes actually using Scala instead of trying to bash and hate it in every thread, you'd know that Scala doesn't use HM.
Scala killer feature is the assurance that developers can express the things they want, unlike Java and C# where the compiler starts acting like an angry child as soon as I want to do anything slightly more elaborate.
That won't be changing anytime soon.
> a far simpler (though less expressive, even though that hasn't been proven to be a major problem) type system
The lack of typeclasses is a non-major problem? I would say it is an absolute dealbreaker.
Anyway, in what sense it is "far simpler"? Most of the complexity comes from dealing with Java's broken ideas. If Kotlin wants interop, it can't ignore that.
If you mean "some developers" or alternatively "some of the things they want" (this set of things being strictly greater than the set of things available in Java), I'll agree with you.
One of the biggest advantages of Scala is the community. Java has a culture of excessive over-engineering, boilerplate and XML. The Scala community tends to think more in terms of a fresh start, rather than seeing themselves as a Java extension. The extreme resistance to change within the Java community and unwillingness to look beyond the only tool in their toolbox makes are also major issues. Every feature is unnecessary complexity and evil until it gets added to Java, and then suddenly the "evil" feature in C# or Scala is suddenly an amazing new "innovation".
Low-boilerplate syntax is certainly a big plus, but I think the biggest feature of scala is that it makes it easier to handle cross-cutting concerns without stepping out of the language. Concretely: a consistent, natural syntax for async calls; better ways of handling errors (validation monad), dependency injection without reflection. And almost as important is the ability to construct DSLs in the language itself (e.g. spray's routing syntax); I know at least one company where this was the primary rationale for adopting scala.
So I think higher-kinded types are a key feature, even if to start with users are only using the libraries built on top of them (you can do specific bodges like C#'s async/await without them, but to have a consistent, extensible syntax that does collections, async calls, and error handling you really need the higher level of abstraction), as are implicits and dependent types (both vital for DSLs). And there were certainly times when I found myself wishing for macros before they existed. Some users might come for the syntax or the traits (though I think error-handling and good async abstractions are at least as appealing, particularly in finance where a lot of the adoption is happening), but you stay for the type system.
Those are the reasons people get in to scala from Java, but not the reason they stay.
Implicit conversion/parameters, higher kinds, and monadic comprehension are the reasons people stay in Scala.
We're spinning in circles with frightening speed indeed, it's the linear speed we're lacking...
Kotlin seems to be one very good alternative in the future.