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simpler implementation while still avoid stack overflow #5

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simpler implementation while still avoid stack overflow #5

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38 changes: 9 additions & 29 deletions index.js
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Original file line number Diff line number Diff line change
@@ -1,36 +1,16 @@
const fromIter = iter => (start, sink) => {
if (start !== 0) return;
const iterator =
typeof Symbol !== 'undefined' && iter[Symbol.iterator]
? iter[Symbol.iterator]()
: iter;
let inloop = false;
let got1 = false;
let completed = false;
let res;
function loop() {
inloop = true;
while (got1 && !completed) {
got1 = false;
res = iterator.next();
if (res.done) {
sink(2);
break;
}
else sink(1, res.value);
}
inloop = false;
}
const isIterable = typeof Symbol !== 'undefined' && iter[Symbol.iterator];
const iterator = isIterable ? iter[Symbol.iterator]() : iter;
let disposed = false;
let result = {};
sink(0, t => {
if (completed) return

if (t === 1) {
got1 = true;
if (!inloop && !(res && res.done)) loop();
} else if (t === 2) {
completed = true;
}
if (disposed) return;
if (t === 1) result = iterator.next();
if (t === 2) disposed = true;
});
while (!result.done && !disposed) sink(1, result.value);
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This might cause infinie loop. U assume in this implementation that u always receive pull immediately in response to pushing the value down

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@franciscotln franciscotln Nov 27, 2018 •
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Could you give an example?
EDIT: you mean a sink calls the source with zero and then doesn't talk back with 1, right?

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pipe(
  fromIter([1,2,3]),
  delay(100),
  forEach(v => console.log(v))
)

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this example works normally. What you mentioned can occur just if for some reason a sink calls the source with 0 and doesn't immediately talkback with 1 or 2. That's true. I just wonder if that's a real scenario, I mean forEach, iterate, subscribe, all of them call source(0, (t, d) => { }) and in case of t === 0 || t === 1 there is an immediate talkback(1). Is that in compliance with the spec? I believe delays should happen through operators and not in the sink by not calling tb(1).

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Implemented sinks (like forEach, subscribe etc) indeed pull automatically - but this is not something that spec assumes. You could also implement backpressurePulls operator that could delay pulls sent upwards and this implementation wouldnt handle it well.

Also from what I see this implementation doesnt handle my delay example (I havent tested it though and I might be wrong). I think it will hang in the while loop, because it will try to send down the same value, rather than next ones.

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I tested it, it works fine if working with delay operators without patching the sinks we know.
In any case, I believe the original version that is implemented by Andre now should include these test cases you mentioned in test.js

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I'm gonna clone the PR because it really doesnt support that a lazy sink that talks back after a delay, thanks @Andarist for the keen eye

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This doesn't seem to be a correct pullable implementation.

A pullable source should only push once for every pull (in a 1:1 ratio), not push everything at once.

if (!disposed) sink(2);
};

module.exports = fromIter;
27 changes: 16 additions & 11 deletions readme.md
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Original file line number Diff line number Diff line change
Expand Up @@ -10,26 +10,31 @@ Convert an Iterable:

```js
const fromIter = require('callbag-from-iter');
const iterate = require('callbag-iterate');
const forEach = require('callbag-for-each');

const source = fromIter([10, 20, 30, 40]);

source(0, iterate(x => console.log(x)); // 10
// 20
// 30
// 40
forEach(x => console.log(x)(source); // 10
// 20
// 30
// 40
```

Convert an Iterator:

```js
const fromIter = require('callbag-from-iter');
const iterate = require('callbag-iterate');
const forEach = require('callbag-for-each');

const source = fromIter([10, 20, 30, 40].entries());
const source1 = fromIter([10, 20, 30, 40].entries());

iterate(x => console.log(x))(source); // [0,10]
// [1,20]
// [2,30]
// [3,40]
forEach(x => console.log(x))(source1); // [0,10]
// [1,20]
// [2,30]
// [3,40]

const source2 = fromIter(new Map().set('a', 1).set('b', 2));

forEach(x => console.log(x))(source2); // ['a', 1]
// ['b', 2]
```
6 changes: 3 additions & 3 deletions test.js
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Original file line number Diff line number Diff line change
@@ -1,5 +1,5 @@
const test = require('tape');
const fromIter = require('./index');
const fromIter = require('.');

test('it sends array items (iterable) to a puller sink', t => {
t.plan(13);
Expand Down Expand Up @@ -69,7 +69,7 @@ test('it does not blow up the stack when iterating something huge', t => {
t.plan(2);
let i = 0;
function* gen() {
while (i < 1000000) {
while (i < 100000000) {
yield i++;
}
}
Expand All @@ -88,7 +88,7 @@ test('it does not blow up the stack when iterating something huge', t => {
return;
}
if (type === 2) {
t.equals(i, 1000000, '1 million items were iterated');
t.equals(i, 100000000, '100 million items were iterated');
iterated = true;
return;
}
Expand Down