arrows and a proposed softCall

Russell Leggett russell.leggett at
Tue Jun 5 09:56:38 PDT 2012

On Tue, Jun 5, 2012 at 12:36 PM, Brendan Eich <brendan at> wrote:

> What I perceive from the JSFixed effort, and from Angus who is good enough
> to post here: people have a particular concern that fat-arrow is too sweet
> and it will lure the children into the witch's house: passing fat arrows to
> dynamic-this APIs.
> We have data suggesting that fat arrows address the dominant use-case,
> thanks to Kevin Smith and others. So fat arrows are in ES6, well and good.
> I think the particular concern about => being an attractive nuisance for
> some APIs such as Angus's mixin combinators, which rely on .call overriding
> |this|, can be addressed by adding -> too. Angus agrees, but -> is not on
> the boards for ES6 (yet).
> We could try to revive ->, but first, we should face the attractive
> nuisance argument squarely, instead of dancing around it with isBound
> abuses that try to "catch fat arrow going into the witch's house".

I think that with ->, a similar problem will still crop up - specifically
that => will be the more common use, and then in the rare case that -> is
needed, people may still use =>. Do we still need isBound to catch that
error as well? Even with the choice of -> or =>, the person writing the
code has to know which one to use and why. That means they have to
understand the whole dynamic |this| problem. I think that the dynamic
|this| behavior of jQuery is not something that should be encouraged. I
understand it is probably mostly that way because of the dom event api, but
that doesn't change the fact that it really has a bad smell to it.
CoffeeScript has ->, but if you look at the examples, none of them actually
make use of dynamic |this| except for methods, and we're adding a nice
method syntax, so it isn't really needed. Method syntax, and => should
cover the majority of cases and lead people down the right path.

I know this is going around in a circle, but my point is that adding ->
doesn't fix the problem, which is devs not knowing when to use => and when
to use function.

- Russ

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