I'm confused about the design constraints on ES4

Brendan Eich brendan at mozilla.org
Sat Nov 10 22:15:41 PST 2007

On Nov 10, 2007, at 10:08 PM, Brendan Eich wrote:

> On Nov 10, 2007, at 9:52 PM, Mark Miller wrote:
>> I'm using "with" here only as an example, to try to understand the
>> nature of the compatibility constraints on the ES4 process.
> Compatibility imposes footprint costs, but it also creates a
> migration tax proportional to usage, roughly. We're trying not to
> blow either footprint budget or migration budget. These are fuzzy,
> hard to quantify and reason about; nice judgment is required.

I meant to add: we're on a slippery slope once opt-in versioning  
means removing stuff if the trade against adding compensating/better  
stuff seems to win. Slide a little way down, fix or remove with and  
bad-eval (keep good-eval, TBD ;-). Slide further, you are starting to  
talk "two languages" and that has brainprint and creeping  
compatibility/shared-code hazards we don't like.

But let's target the bad boys first: with, bad-eval. We've tried to  
reform both. Recidivism is a risk if we misjudge. ;-)


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