Till Schneidereit <mailto:t...@tillschneidereit.net>
October 26, 2013 8:19 PM
On Sun, Oct 27, 2013 at 1:59 AM, Lucio Tato <luciot...@gmail.com
<mailto:luciot...@gmail.com>> wrote:
yield*(curr);
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Lucio Tato <mailto:luciot...@gmail.com>
October 26, 2013 7:59 PM
Rick: I understand. But it is always a trade-off.
If the reason to introduce a new construct is because there may
already be code that defines a function called `yield`, it seems to me
as a bad trade-off. (advantages vs disadvantages)
In your example...
function yield() {... <- will raise a parsing error.
Anyway, there are other ways to solve that.
You can put the asterisk in "yield" instead of the important
"function". It's a lot less confusing.
function fibonacci() {
let [prev, curr] = [0, 1];
for (;;) {
[prev, curr] = [curr, prev + curr];
yield*(curr);
}
}
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Rick Waldron <mailto:waldron.r...@gmail.com>
October 26, 2013 3:08 PM
On Sat, Oct 26, 2013 at 1:01 PM, Lucio Tato <luciot...@gmail.com
<mailto:luciot...@gmail.com>> wrote:
It's really needed to make js syntax more complex in order to
implement generators?
It's function* really needed?
Yes, because `yield` is only reserved in strict mode code, which means
this is valid today:
function g() { yield = 1; return yield; }
Since the starred generator function is a new syntactic form, there is
no existing code that it can possibly break by making yield a keyword.
can you just expose "Generator" as a core function?
can "yield" be a function-call-like-construct instead of a new
language construction?
No, because there may already be code that defines a function called
`yield`, which would be broken if suddenly yield was a special
language-owned function. Consider this:
// your code defines this...
function yield() { return Number.MAX_VALUE; }
// you then include my library, which exposes this fibonacci():
function fibonacci() {
let [prev, curr] = [0, 1];
for (;;) {
[prev, curr] = [curr, prev + curr];
yield(curr);
}
}
What does yield() do? It returns Number.MAX_VALUE every time.
Rick
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Lucio Tato <mailto:luciot...@gmail.com>
October 26, 2013 1:01 PM
It's really needed to make js syntax more complex in order to
implement generators?
It's function* really needed?
can you just expose "Generator" as a core function?
can "yield" be a function-call-like-construct instead of a new
language construction?
function fibonacci() {
let [prev, curr] = [0, 1];
for (;;) {
[prev, curr] = [curr, prev + curr];
yield(curr);
}
}
Generators can be iterated over in loops:
for (n of new Generator(fibonacci) {
// truncate the sequence at 1000
if (n > 1000)
break;
print(n);
}
Generators are iterators:
let seq = new Generator(fibonacci);
print(seq.next()); // 1
print(seq.next()); // 2
print(seq.next()); // 3
print(seq.next()); // 5
print(seq.next()); // 8
Advantages: No new syntax, no "function*" (Cognitive dissonance, every
good C programmer can't stop reading function* as "function pointer").
No "yield" new construction. No added complexity to the language syntax.
By not adding new elements and complexity to the language, you're
keeping it consistent.
By using "new Generator(fn)" to create a Object-Generator, you can
also expose a "done" property and other useful info in a standard way.
Note: why yield syntax should be like a function call:
In actual implementations (V8 --harmony) "yield" will "return" the
value passed in the call to ".next"
functiongiveNext(){//generator
letactual=10;
while(actual<100){
skip=yield(actual);
actual=actual+skip||5;
};
};
letseq=newGenerator(giveNext);
print(seq.next());// 10
print(seq.next());// 15
print(seq.next(20));// 35
print(seq.next());/// 40
//
/*let*seq=newGenerator(giveNext);
while (!seq.done)
print(seq.next());
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