It seems that ES6 will allow implicit opt-in for generators, with the body
of the generator being ES6, so it can yield. It also seems that the plan is
that the body would be forced into strict mode.

The following currently works in Chrome with Experimental JavaScript
Features enabled, but would not work in strict mode, as the eval call
wouldn't execute in the callee's namespace.

function * realm(input) {
    while (true) {
        input = yield eval(input);
    }
}

var r = realm();
r.next();
r.next("var a = 1");
r.next("console.log(a)");

The above functionality is required in an application I'm currently working
on, and there's a few features that would use it. There's actually a large
class of applications that could do so. I'm essentially doing a REPL, and
REPLs are impossible to implement in strict mode. Any app that allows the
user to enter code that'll be executed, needs to evaluate source strings in
a persistent namespace. If that namespace is not `window`, then the eval
call must live in a scope that can yield flow without destroying its local
namespace.

Lots of applications could use this ~ web shells, programming lessons and
games, as well as anything that allows the user to script it.

Is there a story for this kind of application, beyond use V8 and hope
nothing ever changes?
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It seems that ES6 will allow implicit opt-in for generators, with the body
of the generator being ES6, so it can yield. It also seems that the plan is
that the body would be forced into strict mode.

The following currently works in Chrome with Experimental JavaScript
Features enabled, but would not work in strict mode, as the `eval` call
wouldn't execute in the callee's namespace.

```js
function * realm(input) {
    while (true) {
        input = yield eval(input);
    }
}

var r = realm();
r.next();
r.next("var a = 1");
r.next("console.log(a)");
```

The above functionality is required in an application I'm currently working
on, and there's a few features that would use it. There's actually a large
class of applications that could do so. I'm essentially doing a REPL, and
REPLs are impossible to implement in strict mode. Any app that allows the
user to enter code that'll be executed, needs to evaluate source strings in
a persistent namespace. If that namespace is not `window`, then the eval
call must live in a scope that can yield flow without destroying its local
namespace.

Lots of applications could use this ~ web shells, programming lessons and
games, as well as anything that allows the user to script it.

Is there a story for this kind of application, beyond use V8 and hope
nothing ever changes?