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EventStreams circular dependencies in FRP

All examples use Ramdahow _(it clearly shows what the methods do in the contexts of the examples) and kefirhow frp(almost the same API as in bacon.js)

I have a thread that describes a change in position.

var xDelta = frp
    .merge([
        up.map(_.multiply(1)),
        down.map(_.multiply(-1))
    ])
    .sampledBy(frp.interval(10, 0))
    .filter();

It emits +1when I press a key UP, and -1on DOWN.

To get position me scan, this delta

var x = xDelta
    .scan(_.add)
    .toProperty(0);

This works as expected. But I want to limit the value xfrom 0to 1000.

To solve this problem, I found two solutions:

  • Change function to scan

    var x = xDelta.scan(function (prev, next) {
    var newPosition = prev + next;
    if (newPosition < 0 && next < 0) {
        return prev;
    }
    if (newPosition > 1000 && next > 0) {
        return prev;
    }
    return newPosition;
}, 0);

It looks good, but later, when new rules appear, this method will grow. Therefore, I mean that it does not look compositional and FRPy.

  1. current. delta. delta current, current after applying .

    • current delta
    • delta current after applying
    • current after applying current

    , . flatMap.

    var xDelta = frp
    .merge([
        up.map(_.multiply(1)),
        down.map(_.multiply(-1))
    ])
    .sampledBy(frp.interval(10, 0))
    .filter();

var possibleNewPlace = xDelta
    .flatMap(function (delta) {
        return x
            .take(1)
            .map(_.add(delta));
    });

var outOfLeftBoundFilter = possibleNewPlace
    .map(_.lte(0))
    .combine(xDelta.map(_.lte(0)), _.or);

var outOfRightBoundFilter = possibleNewPlace
    .map(_.gte(1000))
    .combine(xDelta.map(_.gte(0)), _.or);

var outOfBoundFilter = frp
    .combine([
        outOfLeftBoundFilter,
        outOfRightBoundFilter
    ], _.and);

var x = xDelta
    .filterBy(outOfBoundFilter)
    .scan(_.add)
    .toProperty(0);

    iofjuupasli/capture-the-sheep-frp

    gh-pages

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2

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e = ((+) <$> b) <@> einput
b = stepper 0 e

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e = ((+) <$> bound) <@> einput
bound = (min 0) <$> (max 1000) <$> b
b = stepper 0 e

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[1]: , , - ( ). stepper - , JavaScript .

+4

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+1

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