And

And applies left and right to the same input and produces a (LO, RO) tuple when both succeed. Evaluation is short-circuit on the left: if left yields Yield.None, right is not applied at all.

Statuses from both sides are merged with combine.

import h8io.stages.*
import h8io.stages.base.*
import h8io.stages.operators.*

object IsPositive extends SAMStage[Int, Int, Nothing] {
  override def apply(in: Int): Yield[Int, Int, Nothing] =
    if (in > 0) Yield.Some(in, Status.Success, this) else Yield.None(Status.Success, this)
}

object IsEven extends SAMStage[Int, Int, Nothing] {
  override def apply(in: Int): Yield[Int, Int, Nothing] =
    if (in % 2 == 0) Yield.Some(in, Status.Success, this)
    else Yield.None(Status.Success, this)
}

val and = And(IsPositive, IsEven)
// and: And[Int, Int, Int, Nothing] = And(
//   left = <function1>,
//   right = <function1>
// )
and(4)   // both succeed
// res0: Yield[Int, (Int, Int), Nothing] = Some(
//   out = (4, 4),
//   status = Success,
//   evolution = Evolution(left = <function1>, right = <function1>)
// )
and(3)   // IsPositive succeeds, IsEven fails
// res1: Yield[Int, (Int, Int), Nothing] = None(
//   status = Success,
//   evolution = Evolution(left = <function1>, right = <function1>)
// )
and(-2)  // IsPositive fails, IsEven not applied
// res2: Yield[Int, (Int, Int), Nothing] = None(
//   status = Success,
//   evolution = Evolution(left = <function1>, right = <function1>)
// )