First off, an example where it works:
a
/5/
7
a / 5 / 7;
However, let's take a more difficult case:
a = function() {}
/5/
7
The reason is that sjs translated the code to:
a = function () {
};
/5/;
7;
(I work on the JavaScript parser for a compile-to-JS language used by people doing jailbroken-iOS development for live introspection of running processes, and thereby that was the first thing I was interested in: how well the parser worked. ;P I have intentions to add reader macros, and then replace all of the extra Objective-C syntax I added with them, but I haven't gotten around to it yet. FWIW: I actually found and fixed a bug in my parser while writing this comment. ;P)
It actually does the right thing if the function is named:
a = function foo() {}
/5/
7
a = function foo() {
} / 42 / 7;
To start with some example code:
for (var a = 7 in /7/ in 9 in b);
TypeError: Cannot use 'in' operator to search for '/7/' in 9
var a = 7; for (a in ((/7/ in 9) in b));
for (var a = 7 in (/7/ in (9 in b)));
ReferenceError: b is not defined
I'm totally willing to believe it, but based on my understanding (which sadly is somewhat limited for Scheme, but fairly in-depth for Clojure) it isn't intuitive to me: it would seem like the way you escape hygiene in Clojure (which by default achieves correct hygiene by attaching namespaces to symbols read for macros or inside of quasi-quote) is quite similar in semantics--but simpler in practice due to being exceedingly less verbose--than using syntax->datum and datum->syntax.
Hygiene is (roughly speaking) about getting scope right by default but has never been about forcing it on the programmer. Moreover, there are two components to it, only one of which is easy to achieve in an unhygienic system. It's easy to ensure your macro renames introduced /bindings/ by using gensym. But if your macro introduces /references/ to existing variables, it's very hard to protect against those references getting captured at the site where clients call your macro.
I believe in Clojure they get around this for some cases by letting you fully qualify a reference to a library binding, for example. But what if your macro wants to refer to a variable that's local to it? Such as an unexported library function, or simply a local variable. Again, I don't know if Clojure has an answer to this.
One concrete example: write a `define-inline` macro-defining-macro. At the call site, a user might write
(define some-local-variable /* something */)
(define-inline (foo x)
(+ x some-local-variable))
(define some-local-variable "something else")
(foo 42)
I do agree that the state of the art in hygienic macros is too complex. I just haven't seen another system that makes this kind of thing work. But I would like to experiment with Clojure's macros more to see if they have an answer.
Dave
'Wish the function keyword in JavaScript wasn't so long? What if you could define functions with def instead?'
Erh, no? Why in the lord's name would I ? Is that your big selling point? 'I don't like function() because it's too long?'
'Want a better way to make "classy" objects?'
<provides example that looks like php vomited on Javascript after mating with ruby>
Why would you want to make javascript less like javascript, introduce a dependency to javascript that can read your language, and then compiles back into javascript in realtime, in a way that will obviously make debugging nearly impossible (like coffeescript)?
Am I the only one that doesnt understand the use case of this? Or should this have been presented as just another lexer/parser?
The description page (like the rest of the project at them moment) is definitely a work in process. Sorry about the confusion!
> 'Wish the function keyword in JavaScript wasn't so long? What if you could define functions with def instead?'
> Erh, no? Why in the lord's name would I ? Is that your big selling point? 'I don't like function() because it's too long?'
This is just a really basic example of what you can do. Obviously you could have the same effect with sed but we need something simple to shows what basic macro definitions look like.
> 'Want a better way to make "classy" objects?'
> <provides example that looks like php vomited on Javascript after mating with ruby>
I'm assuming you refer to the macro definition with $ and whatnot. If you have ideas for better syntax please contribute! The notation is by no means final. That said I think it's pretty good for what it needs to do, matching syntax patterns and transforming them into new bits of syntax. Certainly more readable than a full parser/compiler.
> Am I the only one that doesnt understand the use case of this? Or is it just another lexer/parser?
The idea is to provide a middle way between no syntax extensions and writing your own full compile-to-js language languages like CoffeeScript which allow you to add any kind of syntax you want, but at the expense of being able to compose extensions. If you like the class notation of CS you must buy into all the syntax choices of CS whereas macros allow you to add just the syntax you want.
Whether you want new syntax is of course a different question. Other languages like scheme and closjure have found macros useful so sweet.js is an experiment to find out if the same syntactic extensibility that they provide is useful in JavaScript.
Hope that helps!
How about a more clear description like above on your page with some readups into macro's, and some more complicated examples that tell me as a programmer: "Yes, I dó need macro's!" and I can use them for these and these cases?
Also, don't underestimate how smart your audience is going to be by giving them just 3-line examples. I always find it more clear when there's some actual use cases on the wiki pages. How about a proper class, or a todoMVC style demo, so that people can actually imagine what kind of possibilities this would unlock?
Regardless, if you don't like macros (and your arguments are common among people who don't; that said, they are also common arguments against using higher-level languages or even functions), then you won't like this project or any other project attempting to provide similar functionality. ;P