Jon Zeppieri wrote:
>> Suppose you're reading someone else's code:
>>
>> var a = 0; // Say you have noticed this declaration.
>> // Several lines of code.
>> for (let a = a; a < 10; a++)
>> { // Several lines of code.
>> let x = a; // Have you noticed the change in meaning?
>> }
>> let y = a; // Are you aware that a is unaffected by the loop?
>
> I don't find this confusing, at all. I think it could become
> confusing if there were redundant declarations of the same variable,
> as allowed by var.
Obviously the confusion occurs only if you miss |let a=a|, not if
you see it. Program maintenance becomes more expensive when you
must painstakingly look for things like |let a=a| everywhere.
> Non-recursive bindings are sometimes useful (particularly for simple
> code generation).
It seems trivial to use different names. I really don't get this.
Is there a shortage of letters?
> After thinking about this a bit more, I don't know what single binding
> semantics to prefer:
>
> let: closest to the immediate function expression + application
> pattern in common use
> let*: like let, but with left-to-right evaluation
> letrec*: closest to current 'var' behavior
If it's like var, people can re-use their knowledge about var.
Let them spend their learning time on more useful things than
tiny scoping intricacies.
>> For very small and simple projects it's great that JavaScript lets
>> you sprinkle your declarations all over the code, with redundant
>> repetitions if you like. Block scope should be available also with
>> this usage pattern, in my view.
>
> I *do* know, however, that I don't like this.
>
> I think you, Ingvar, are the lone champion of redundant variable declarations.
Earlier I declared variables only once, and would sometimes
forget. The bugs cost time. With var on every initialization
the problem disappears.
As a result, the lack of var has become a warning that I notice
very clearly. Do I really want global here? I'd prefer an "outer"
declaration, but have to use the lack of var instead.
> I'm not sure who the champions of var hoisting are. (In another
> thread, Brendan referred to hoisting as a wart.)
That's me too, but it was combined with things that made hoisting
all but disappear. Unfortunately my explanations were bad, and
the proposal drowned under claims that I was instead proposing
something very different and very unworkable that I never intended,
and persistent attacks against this strawman.
I did learn a lot about how to explain better, so maybe I could
try again and get across this time. The real proposal was beautiful
simplicity both in usage and implementation.
>> Let statements might also enable throwing an error on undeclared
>> names.
> I can't imagine what you have in mind here.
let (a = 3)
{ x = 5;
}
If you put |let (a = 3)| above your block, this might tell the
compiler that you want everything neatly declared at the top,
and therefore want an error thrown at the undeclared x. A strict
mode regarding declarations.
--
Ingvar von Schoultz
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