[saebekassebil]

May be off-topic but: Is it just me, or are macros just a new way to get confused while reading JavaScript? Introducing language-foreign syntactic constructs seems to me superfluous and confusing - This is the job of transcompiling languages like CoffeeScript.

[BrendanEich]

Reading the macros first helps. They must be defined at top of program or module, if I recall sweetjs.org's design correctly, for the staged hygienic expansion to work well.

Aside from that, you're right. But JS has higher order functions and objects with ad-hoc methods, so it can be used according to many paradigms, which can make it hard for a reader unfamiliar with the dominant paradigm in code at hand.

This is not a deal-killer for macros, although with sweet.js as the prototyping tool, your assertion about "This is the job" is satisfied. Sweet.js works with node to do AOT macro expansion at present. There's effort to integrate it in the browser too, but this will be easier with ES6 module loaders (not yet prototyped in SpiderMonkey or V8).

[saebekassebil]

Of course, as in every aspect of understanding, here for source code, it is important first to learn the context, here the macro definitions. My concern is that this will impose more than just a paradigm - it will impose new syntax which could effectively completely ruin the readability of JavaScript source.

The macro syntax is definitely not simple, and it could possibly get really complex for more elaborate syntactic definitions, thus rendering the source much less readable. Is the overall benefits of introducing macros to JavaScript really worth the costs of readability? And does the effort to integrate macros into the browser mean that it'll be possible to evaluate macros "runtime"?

[disnet]

> The macro syntax is definitely not simple, and it could possibly get really complex for more elaborate syntactic definitions, thus rendering the source much less readable.

True, but the same can be said of any API. Reading the definitions can help but for both complex macros and complex APIs built today out of just functions and objects you need to document your abstractions. Macros don't change this, they just give you another abstraction axis (syntactic) to work with.

As with most things it just depends on how you use it. Sure you can abuse macros to make tons of crazy, undocumented, hard to understand syntactic extensions that destroy readability. But you can already do that today. Used wisely macros can increase readability, used poorly they can decrease it.

> And does the effort to integrate macros into the browser mean that it'll be possible to evaluate macros "runtime"?

Not sure what you mean here. By definition macros are expanded at compile time (well, parse time really). The browser doesn't change this.

[saebekassebil]

I meant compile time of course, thank you for your clarifications. I'm eager to see how this turn out.

[dherman]

All abstractions can make your code unreadable; the key, as always, is to create good abstractions and document them clearly. Macros are syntactic abstractions. It's just as important to document them as it is for functions or objects. Of course, if you just have a little local macro that you're using for convenience, looking at the implementation may be sufficient. But when you write a macro that you want to share from a module, rather than requiring your clients to read the implementation, you document the syntax and the semantics, just like you would if you were writing a separate language.

But by having macros directly in JS, instead of having to use a whole language that compiles to JS, you can combine syntactic features from different sources. For example, right now there's no way to use one feature you like from CoffeeScript with another feature you like from TypeScript. You just can't combine them. But with macros, you could import two different syntaxes from two different libraries and use them in the same code.

On top of that, if we actually had macros in a future version of the standard, you wouldn't even have to precompile the macros offline, and you wouldn't need a preprocessing step at all. (For latency purposes, you might want to preprocess macros offline as an optimization. But for development, not having to do a preprocessing step is more convenient.)

Dave

[saebekassebil]

So this is all in the holy name of making JavaScript the assembly language of the web? Making it possible for every JavaScripter to write "his own" JavaScript syntax definitions meaning that I'll (as a contributor or just casual watcher) would have to read his whole collection of macros before I could begin to understand the code?

I don't think this can be compared to API's as they still follow the regular syntactic definitions - This will be like reading a completely new language every time I read a different repository. (Of course this is a worst-case scenario as I imagine that many macros will be used across several projects, but still.)

Is all hope gone for writing vanilla JS gone? And isn't macros kinda going in the opposite direction than the ES specs? There's no use for many of the ES6/7 features as they could just be mocked up in macros.