On Wed, May 11, 2011 at 10:31 AM, Andreas Rossberg <[email protected]>wrote:
> On 11 May 2011 18:31, Mark S. Miller <[email protected]> wrote: > > On Wed, May 11, 2011 at 4:42 AM, Andreas Rossberg <[email protected]> > > wrote: > >> > >> Thanks to everybody for clearing up my confusion. The thing I had > >> missed in the spec was Section 10.4.2. And of course, my example was > >> too simplistic because it couldn't distinguish caller and global > >> context. > >> > >> At the risk of reviving old discussions, are there any sources > >> explaining the rationale behind the current design? The "obvious" > >> solution to me would have been having two internal variants/modes of > >> (or "entry points" to) the eval function, one strict, one non-strict. > >> And depending on the lexical strict mode, the identifier "eval" would > >> be bound to the right one. > > > > I don't think I understand the suggestion. What would the following code > do: > > // non-strict outer context > > function f(eval) { > > var f = eval; > > function g() { > > "use strict"; > > eval(str); // [1] > > (1,eval)(str); // [2] > > f(str); // [3] > > } > > } > > [1] If the outer eval is bound to the global eval function then this is a > > direct eval, which therefore lexically inherits strictness. So no problem > > here. > > [2] The 'eval' identifier is bound in non-strict code and used in strict > > code. > > [3] Strict code makes no use here of a lexical binding of the identifier > > "eval". > > > > A previous approach which we rejected was to make strictness dynamically > > scoped, so all three of the above calls would do strict evals. This was > > rejected to avoid the problems of dynamic scoping. Are you suggesting a > rule > > that would affect #2 but not #3? If so, IIRC no such rule was previously > > proposed. > > I'm actually suggesting plain lexical scoping. :) > > Basically, what I'm saying is that the directive "use strict" could > simply amount to shadowing the global eval via an implicit "var eval = > eval_strict" (unless global eval has already been shadowed lexically). > So all uses of the identifier `eval' in that scope would refer to its > strict version, no matter when, where, or how you ultimately invoke > it. Consequently, all your three examples would behave the same, only > depending on the argument to f. > I don't understand. If "use strict" implicitly introduces a "var eval = eval_strict;" at the position it occurs, then wouldn't #3 in my example still evaluate non-strict? I'll answer the rest once I understand your proposal. > Re dynamic scoping: in fact, I would claim that the current rule _is_ > a form of dynamic scoping -- eval behaves differently when its caller > is strict. Except that this rule only applies when the syntactic > identifier in the call happens to be "eval". Regardless of the above, > I wonder why this special case was introduced. Why is the rule not > applied to all applications uniformly? I feel that I am missing > something. > > /Andreas > -- Cheers, --MarkM
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