[jarcane]

I was literally complaining today about the fact that no-one seems to have yet implemented that part of the ES6 standard yet[1], and yet now here it is.

As someone chiefly interested in .js for it's 'functional curious' side, the new features in ES6 have me really excited.

[yoshuaw]

Which parts of es6 would you call 'functional curious'?

[jarcane]

What I mean is, JS in general is not a Lisp, nor is it a functional language.

But it does have a number of key basics in place. It has anonymous, first-class functions and objects. It has a very handy function composition syntax (chaining dot-notation feels almost like Haskell sometimes, if uglier). It has map(), filter(), and reduce(). You can, somewhat torturously, wrangle a Y-combinator in it even.

But in practice, it's still missing some basic toys. The lack of TCO means that while yes you have handy function composition and a basic smattering of first-class functions, recursive solutions aren't really viable, which makes many classic functional approaches impossible when it comes to implementing the stuff that isn't there yet. You have to kludge around it with mutation and for loops and such. As well, you also run into issues with the object-oriented focus at times: first-class functions are all well and good, but not that useful when so many things aren't functions but methods or operators, requiring even more heavy use of lambdas than I would in a Lisp.

ES6 goes further in the direction of supporting the functional style and making it more pleasant to write. Arrows offer neater lambda syntax, let and const offer better control of scope and enforced immutable variables, and of course offering proper TCO opens up a lot easier implementation of classic recursive functions. I'm even a little curious about the possibilities of iterators and generators; my experience implementing an RNG in Heresy using Racket's generators suggested that they can prove a powerful tool in the functional programmer's toolbox for solving certain kinds of problems traditionally thought to be quite non-trivial to write from a functional approach.

ES6 does come a little closer to actually living up to Crockford's hype with these changes. It's something I'm very excited to keep learning and playing with, and it was something of a relief to find a niche for the happy little Schemer in me in an otherwise very mainstream, mostly-imperative language.

[angersock]

There is a lot of good stuff in there.

I have to ask, though: what the tap-dancing Christ was the purpose of the new Symbol objects? They're completely alien to any other symbols implementation I've seen.

They aren't global by default, they don't compare equally to one another, and even the global ones can't really be used for, say, KV lookups in a global table. WTF?

[mjn]

I believe they're similar to uninterned symbols in Lisp, i.e. what you get in Common Lisp from make-symbol (or gensym). The main intended use-case seems to be to get "private" property names, by conjuring up a fresh name-like thing is not equal to any other name-like thing, and not findable/enumerable in the usual way either. You can then monkey-patch that into a class or do whatever other nefarious thing you were planning.

I agree it's a somewhat confusing name, since interned symbols are the more familiar kind of symbol in other languages, especially in the modern era (older Lisps made more extensive use of uninterned symbols).

[angersock]

So, that sort of makes sense if you were to use them as keys in the new Map and Set objects...but I again, I can't help but notice that I haven't felt their absence yet.

Thanks for the reference about CL make-symbol. Is there a practical use for this we actually would spot in the wild, or do I need to go up on the mountain with a copy of The Art of the Metaobject Protocol?

[fpgeek]

The standard Lisp use for generated symbols is to provide a way to reliably avoid name clashes during macro expansion.

I'm not sure if that qualifies as a practical use in the out in the wild or just a practical way to fix pain (e.g. CPP nonsense) that you can see out in the wild.

[rnbwd]

I had no idea what a Symbol even was until I stumbled upon alt - https://github.com/goatslacker/alt

It's a small and simple code base, and much easier way to grok the concept than reading a book.

[kaonashi]

With destructuring and tco, the only thing its really missing is pattern matching on multiple function bodies.

[jarcane]

This is the single biggest thing I miss from Haskell when programming in other languages.

Pattern-matching and guards are crazy useful.

[kxo]

This would be the ultimate feature. Languages with dynamic dispatch would do well to implement this feature.