I think he's proposing that the 'eval' function would be a magical function that can inspect its calling environment to determine whether it's being called in a lexically strict context or not, and based on that it would act like the strict eval operator, or not.
On Wed, May 11, 2011 at 11:30, Mark S. Miller <[email protected]> wrote: > > > 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 > > _______________________________________________ > es-discuss mailing list > [email protected] > https://mail.mozilla.org/listinfo/es-discuss > > _______________________________________________ es-discuss mailing list [email protected] https://mail.mozilla.org/listinfo/es-discuss
