ES6 opt-in, reloaded

Axel Rauschmayer axel at
Mon Jan 16 09:53:45 PST 2012

> Compared to Dave's original proposal, the only scenario on which it
> loses re (1) is if the program already consists of a module, in which
> case you'd still have to write the opt-in declaration. One can
> probably argue whether this is worth adding an extra rule (personally,
> I don't think so). If so, it would be enough to say that a module
> declaration as the _first_ statement in the program also opts in _all_
> of the program.
> In either case:
> 1. You always opt in all of the program consistently.
> 2. It is obvious from the first line that you do.
> 3. This truly opts-in the toplevel (for whatever that means in detail).
> 4. A future ES programmer just needs to know one rule: start your
> program with _____.


My main concern: things should be dead simple to learn and/or explain. Andreas’ proposal is, what has been discussed so far *might* also eventually be, but I don’t see it (yet).

Claus Reinke’s recount of lessons learned by the Haskell community in this area also seems relevant:


Dr. Axel Rauschmayer
axel at


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