Does ES6 Tail Call Optimization Cover Generators?

问题

Does ES6's support for tail call optimization cover tail calls in generators?

Suppose I have this generator for integers >= 0:

var nums = function* (n) {
    n = n || 0;
    yield n;
    yield* nums(n + 1);
};

Currently, in Chrome and Firefox, it adds a stack level with each recursive call and eventually runs into a "maximum call stack size exceeded" error. Will this still occur once ES6 is fully implemented?

(I know I can write the above generator iteratively and not run into the error. I'm just curious about whether TCO will take care of recursively defined generators.)

回答1:

When a function call is made, according to the section Function call evaluation,

8. Let tailCall be IsInTailPosition(thisCall)
9. Return ? EvaluateCall(func, ref, arguments, tailCall)

The call will be evaluated based on the IsInTailPosition's result. And if if we check IsInTailPosition,

5. If body is the FunctionBody of a GeneratorBody, return false.

So, if the function body is a generator, then Tail Call Optimization will not be done.

来源：https://stackoverflow.com/questions/30135916/does-es6-tail-call-optimization-cover-generators