Basic Lambdas and Explicit Tail Calls Repackaged

Brendan Eich brendan at mozilla.com
Sun Dec 7 23:51:19 PST 2008


On Dec 7, 2008, at 11:43 PM, Michael Day wrote:

> Hi Brendan,
>
>> I say 1 trumps 2 for the reason given in the last paragraph: human  
>> programmers first, meaning the fat bell curve (sorry, Schemers).
>
> I agree with this; there are all sorts of clever things that  
> implementors can do that don't necessarily need to be exposed as  
> features in the language standard.
>
> However, as Eugene Lazutkin pointed out, is omitting 'this' and  
> 'arguments' a sufficiently compelling improvement to justify  
> introducing a whole new language construct?

I believe this is Waldemar's view too, which along with his objection  
to the completion-value hazard leads to the "improve functions through  
strict mode or a new version" approach.

There's a lesser goal I didn't list: make function syntax thinner.  
'function' is eight whole letters, plus four chars of parens and  
braces, plus 'return'. Wherefore expression closures in JS1.8 -- they  
save the braces and 'return' overhead. But to fix expression closures  
to be bottom-up unambiguous we would require at least parens around  
the body-expression.

More concise function syntax is not a goal solely, or even  
exclusively, to support user-defined control abstractions. It's a good  
in its own right unless you consider every use of a function  
expression in JS today to be a control abstraction in the Smalltalk  
block sense (I do not).


> In some cases in strict mode 'this' will be undefined instead of  
> being the global object, does this come close enough to omitting  
> 'this' for functions which are not methods?

Not really -- strict mode does not change the ability of |this| to be  
rebound in the absence of Function.prototype.bind usage, which has its  
costs, and which apart from overhead in implementation terms, takes  
too long to say in the language to be likely as a default practice.  
Sure, Ajax libraries use it well, but it's still observed more in the  
breach looking at the whole of "web JS".

/be


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