Fat arrows!

[ryanseddon]

Fat arrows implementation covers most cases.

Fixes #1

[ryanseddon]

I'd love to be able to cover no prototypes and clobbering arguments if that's possible. Any ideas?

[jlongster]

Yay, been looking forward to this one! I recently updated my repo to work with the latest sweet.js, and if I merge in this I'm hitting a bug with sweet.js with how my destructuring var and => plays. Once I fix that (in sweet.js I think) I'll think more about comment #2.

[jlongster]

I filed the bug here: https://github.com/mozilla/sweet.js/issues/271. Not sure which version of sweet you are using, but the internals have changed quite a bit in the past 2 months.

[jlongster]

Actually, I think it was mainly a bug in my code. The :expr on the lhs of a var was eating the whole assignment and messing up how things were expanded. This has made us think through how we handle a few things internally though.

Everything looks good, thanks a lot for this!

[jlongster]

We could check for arguments by parsing the function body code in a case macro. I do this in the class macro (the code is ugly right now). We could be really smart and check to see if arguments is not locally defined, and if found we would throw an error (or maybe just a warning).

This would add a bunch of code the macro, but we probably should do it at some point. I'm not too worried about it right now though.

I'm not sure if we can strip the prototype of it. Is there a valid way in ES5 to do that? Is it safe to just set f.prototype = undefined? If so we could probably get that in here.

[ryanseddon]

If we were to compile without hygienic renaming we could easily do the following

macro => {
  rule infix { ($value (,) ...) | {$body ...} } => {
    function($value (,) ...) {
     arguments = undefined;
     $body ...
    }.bind(this)
  }
  rule infix { ($value (,) ...) | $guard:expr } => {
    function($value (,) ...) {
     arguments = undefined;
     return $guard;
    }.bind(this)
  }
  rule infix { $param:ident | $guard:expr } => {
    function($param) {
     arguments = undefined;
     return $guard;
    }.bind(this)
  }
}

As for the prototype if we could access the function, setting the protoype to undefined would work too.