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Comment by tanlermin | Hacker News Reader

Do you see it replacing python for non DS? What is on Julia 2.0?

I think there's a general misconception that Julia is a DS/scientific programming focused language. It just so happens that these are areas where its advantages are most apparent, and give the biggest early wins. Given enough time, though, I think the paradigms that Julia is exploring will make it a killer general-purpose language.

As for Julia 2.0, it was decided to put off implementation of traits and interfaces until then. That said, some of the ideas that were being bounced around during the post-con Hack day in these areas are really exciting. In short: Julia may be the first language to pull off behavioral typing in a practically usable way.

"Given enough time, though, I think the paradigms that Julia is exploring will make it a killer general-purpose language."

I think its already a Killer general-purpose language (except for the module system).

I'm just not sure if it is good enough to unseat incumbents when there are things like rust with its deterministic memory management or python with all its momentum and compiler technology coming along.

Not sure whether to bet on it at this point.

The thing about Julia is that it's playing a whole different ballgame than pretty much every other popular language today...it's just that most people don't realize it yet! The work and design that's gone into Julia's type system and multiple dispatch has the potential to be a real game-changer, but outside of a core community putting it to good use, I don't think it's potential has been fully realized.

This is also why I'm excited by what's coming next in v2.0. Some of the early ideas being explored at JuliaCon with respect to traits and interfaces will begin to really shine a spotlight on its true power.

> The thing about Julia is that it's playing a whole different ballgame than pretty much every other popular language today

I've noticed this. I've been using it the past four years for much of my dissertation work (starting right when it was released). Julia's type system has the potential for some extremely cool things.

I've been toying around with the idea of making a package that focuses on runtime static typing. This would be particularly useful when using the language interactively (like in a Jupyter notebook). The idea is to perform a check at runtime to make sure all variables in a function are assigned an immutable, concrete (non-abstract) type, and then compile an optimized version of that function on-the-fly . One source of pain in a lot of my Julia code is that unintentional type instability contributes to a lot of unnecessary performance penalties, and it takes quite a bit of poking and prodding before I figure out exactly which line is responsible. Forcing a check over the function would prevent these occurrences.

I also seem to have the problem of inadvertently calling functions that allocate and deallocate tiny amounts of memory on the innermost for loops.

(Then again, maybe nobody else has these issues and I'm just bad at deducing when AbstractVector can't be used.)

It is unmaintained now, but you might want to have a look at [1], which builds on the type inference system to add some static checks. I believe there may also be some related work in [2].

> Then again, maybe nobody else has these issues and I'm just bad at deducing when AbstractVector can't be used.

Nope, not just you. This is definitely an issue.

[1] https://github.com/astrieanna/TypeCheck.jl [2] https://github.com/tonyhffong/Lint.jl

> In short: Julia may be the first language to pull off behavioral typing in a practically usable way.

I haven't heard of behavioral typing before. What would be an example (or pseudo-example) of this?

Up until now it's been the realm of PL research. The Ptolemy language is one example I know of: http://citeseerx.ist.psu.edu/viewdoc/download?doi=10.1.1.86.... [PDF]

If you're familiar with duck typing, behavioral typing is (in essence) the reification of duck typing in a concrete type system. In other words, instead of specifying the type of your argument as "Array", you could specify "some type that is indexable, iterable, and can be appended to".

In Julia (mind you this was just the idea I saw being considered), today you would do:

    function foo(myarray::AbstractArray)
      ...
    end

but in the future you might be able to do something like:

    function foo(myarray::ANY{getindex(), setindex(), iterate(), append()})
      ...
    end

what's really neat, though, is combining this with type aliases, you could have:

    typealias Arraylike ANY{getindex(), setindex(), iterate(), append()}
    function foo(myarray::Arraylike)
      ...
    end

Unless I'm mistaken, this seems to already be available in Scala and is called "structural typing"[0]. Is there a substantial difference?

[0]: https://dzone.com/articles/duck-typing-scala-structural

The difference between structural typing and behavioral typing is subtle. In Scala, you're essentially asking the type system to check for the presence of a member function on the object with a specific type signature. Since the function is contained within the object, you're still only typing based on the object's structure (hence: structural typing).

In Julia, objects are data-only and methods are defined at a module level. So, whereas Scala's structural typing need only introspect the object being passed as an argument, Julia's behavioral typing requires introspection of the entire dispatch tree. The benefit to behavior typing and Julia's multi-dispatch is that if you are missing one or two methods for some type in order to be able to use it in some function, you can always define the missing methods locally.

Great explanation, thank you.

You could also view C++ templates as a kind of behavioral typing, although the experience of using them in that way is not very pleasant. Concepts should help clean that up when they finally arrive in the spec.

It seems like the weak spot for using Julia outside of scientific computing is deployment to interesting targets.

For example, with Go you can build a standalone executable in many platforms, and other languages run on interesting targets like browsers or phones, or run on the JVM.

Any news on that front?

Yes. Module pre-compilation is already possible, and last I heard there is work underway to use the same sort of mechanism to allow for single-executable compilation. The problem, of course, is that Julia and Go are very different beasts, and pre-compilation will almost certainly limit some of the currently available dynamism. (Already there are packages that cannot be pre-compiled due to these limitations.)

Of course, in this regard Julia is not any different than Python, Ruby, JS, PHP, etc. Also, it's worth noting that Julia has cluster-computing as a concept baked into the language. So, whereas you might need to worry about distributing Go executables to multiple machines in a cluster, with Julia you need only have the Julia runtime installed, and from there any Julia program can distribute itself to any available nodes without further action required.

The juliacon videos are online. See here for Julia 2.0: https://www.youtube.com/watch?v=5gXMpbY1kJY&t=1250

I hope so, at least since they care about performance instead of outsourcing to C.

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