[英]side-effects for `wye` combinators when using `halt` from scalaz-stream
filter
(which uses halt
inside) terminates other branch even if it has some side-effects: filter
(内部使用halt
)终止其他分支,即使它有一些副作用:
scala> val p = Process("1","2", "3")
scala> val p1 = p.filter(_ => true).map(_ + "p1").observe(io.stdOutLines)
scala> val p2 = p.filter(_ => false).map(_ + "p2").observe(io.stdOutLines)
scala> (p1 yip p2).run.run
1p1
scala> val p2 = p.filter(_ => true).map(_ + "p1").observe(io.stdOutLines)
scala> (p1 yip p2).run.run
1p1
1p2
2p1
2p2
3p1
3p2
Seems logical as there is no value to be returned to yip
after that filter
. 似乎合乎逻辑,因为在该
filter
之后没有值要返回到yip
。 But what about side-effects, specified with observe
? 但是
observe
的副作用呢?
My current solution is to use flatMap
to specify default value: 我当前的解决方案是使用
flatMap
指定默认值:
scala> val p1 = p.map(_ + "p1").flatMap(x => Process.emit(x).observe(io.stdOutLines))
scala> val p2 = p.map(_ + "p2").flatMap(x => Process.emit(""))
scala> (p1 yip p2).run.run
1p1
2p1
3p1
But maybe there is a way to use filter
? 但是也许有一种使用
filter
吗?
PS merge
combinator executes side-effects for other branch (as it doesn't require value to be returned), but it doesn't wait for other branch if one halts (even if it has side-effects). PS
merge
组合器为其他分支执行副作用(因为它不需要返回值),但是如果一个分支暂停,它就不会等待其他分支(即使它具有副作用)。
To run the effects even after p2 terminates there needs to be clear default
behaviour. 即使在p2终止后也要运行效果,需要明确的
default
行为。 So there are probably these solutions: 因此,可能有以下解决方案:
p2
to supply default value after being terminated p2
以在终止后提供默认值 either
wye to get left and rights if we don't really need tuples either
来获得权利 perhaps the (1) is closer to question and code will looks like: 也许(1)更接近问题,代码看起来像:
val p = Process("1","2", "3")
val p1 = p.filter(_ => true).map(_ + "p1").observe(io.stdOutLines)
val p2 = p.filter(_ => false).map(_ + "p2")
.observe(io.stdOutLines).map(Some(_)) ++ emit(None).repeat
// alternativelly
// val p2 = p.map { v => if (pred(v)) right(v) else left(v) }
// .observeO(o.stdOutLines).flatMap { _.toOption }
// ++ emit(None).repeat
(p1 yip p2).run.run
Actually it should be just something like that: 实际上,应该是这样的:
in.map(emit).flatMap{ p =>
val p1 = p.map(_ + "p1").filter(_ => true).observe(out)
val p2 = p.map(_ + "p2").filter(_ => false).observe(out)
p1 merge p2
}.run.run
It makes all side effects being in order as filter
can't get more than one value (produced by emit) 它使所有副作用都井井有条,因为
filter
不能获得一个以上的值(由发出产生)
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