I am one of those on TC39 that want the visible flag. Since, in my view,
the only non-mistaken need to preserve sloppy mode is as an ES3
compatibility mode and ES3 has no generators, I consider this flagging
issue to be the important one. Yes, you have to read the function to know
*what* it generates. But even before you've figured that out, your whole
effort to read the function is different once you know you're reading a
generator function. Better to know it early.
But that is a *semantic* property - you can't force it into *syntax*.
Consider this code:
// run with node --harmony
function* gen() { yield 1 }
function f(g) { return g() }
console.log( f(gen).next() ); // { value: 1, done: false }
You can't see by looking at 'f' that it can return an iterator. And 'f's
parameter and return value could even vary dynamically.
I could imagine a type system for this, which would be nice (just as it
would be nice to have a type system telling you whether a callback-taking
function uses the callback async, sync, or both). Then your IDE could tell
you (an approximation of) what you're dealing with, providing verified
API documentation. But I don't see how to do that with syntactic tools only.
Code is read much more than it is written -- at least code that matters.
For this reason, I would still suggest to separate generators from 'function' -
there is nothing function-specific about generators (apart from generator
implementations using stack frames, perhaps), so I find it confusing to
mix up these two concepts. It also keeps us from using arrow functions
freely with generators.
I did suggest using something like 'do* { yield 1 }' as generator syntax
(ie, 'do*{}' would be an expression denoting an iterable, and 'yield' could
only appear in 'do*{}'). It still has the syntactic flag, but it separates functions
and generators. We could then recombine the two as needed, without
complicating the 'function'-related specification machinery:
let gen = v => do* { yield v };
gen(1).next() // { value: 1, done: false }
Claus
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