Starting and stopping a stream based on values from another stream

[sammosampson]

For example I want to start an 'every' pulse stream when another stream changes value and pause it when the other stream changes to another value. Any ideas on the best way to do this?

[c-dante]

Streams in flyd are always active (to use kefir terms) -- that is, they're more like a property than a stream.

There is no way to "enable" or "disable" a stream, but you do have a ton of control through the combine api.

From what I gleam off your request, you can do something like:

const debug = (name, s) => flyd.on((x) => console.log(name, x), s);
const a = flyd.stream(); // Start undefined
const b = flyd.stream(0); // Start at 0

const c = flyd.combine((a, b, self, changed) => {
  if (b() % 2 === 0) {
    c(a())
  }
}, [a, b]);

debug('a', a);
debug('b', b);
debug('c', c);
a(0);
b(1);
a(10)(15);
b(2);
a(1)(2)(3);

/* Expected:
b 0
a 0
c 0
b 1
a 10 // Notice that c skips 10 because b was odd during this call
a 15
b 2
c 15
a 1
c 1
a 2
c 2
a 3
c 3
*/

Again, not 100% on your use case or what you directly mean, but I'm demonstrating a way to use flyd.combine for some interesting logic. In this example, if b is even than c takes on a's value, otherwise c is "frozen".

You could also keep c's state outside in a closure, if that's easier to work with.

[sammosampson]

Excellent this is exactly what I need thank you for this.

Chris

On 19 Apr 2016, at 20:59, Dante notifications@github.com wrote:

Streams in flyd are always active (to use kefir terms) -- that is, they're more like a property than a stream.

There is no way to "enable" or "disable" a stream, but you do have a ton of control through the combine api.

From what I gleam off your request, you can do something like:

const debug = (name, s) => flyd.on((x) => console.log(name, x), s); const a = flyd.stream(); // Start undefined const b = flyd.stream(0); // Start at 0

const c = flyd.combine((a, b, self, changed) => { if (b() % 2 === 0) { c(a()) } }, [a, b]);

debug('a', a); debug('b', b); debug('c', c); a(0); b(1); a(10)(15); b(2); a(1)(2)(3);

/* Expected: b 0 a 0 c 0 b 1 a 10 // Notice that c skips 10 because b was odd during this call a 15 b 2 c 15 a 1 c 1 a 2 c 2 a 3 c 3 */ Again, not 100% on your use case or what you directly mean, but I'm demonstrating a way to use flyd.combine for some interesting logic. In this example, if b is even than c takes on a's value, otherwise c is "frozen".

You could also keep c's state outside in a closure, if that's easier to work with.

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[StreetStrider]

flyd-keepwhen flyd-cacheUntil

[c-dante]

If this is resolved, can you close this issue @sammosampson or @paldepind?