Note: Spool is no longer the recommended asynchronous stream abstraction. We encourage you to use AsyncStream instead. See Spools for the Java adaptation of the Spool companion object.

A spool is an asynchronous stream. It more or less mimics the scala {{Stream}} collection, but with cons cells that have either eager or deferred tails.

Construction of eager Spools is done with either Spool.cons or the {{**::}} operator. To construct a lazy/deferred Spool which materializes its tail on demand, use the {{*::}} operator. In order to use these operators for deconstruction, they must be imported explicitly (ie: {{import Spool.{*::, **:: }}} )

def fill(rest: Promise[Spool[Int]]) {
  asyncProcess foreach { result =>
    if (result.last) {
      rest() = Return(result **:: Spool.empty)
    } else {
      val next = new Promise[Spool[Int]]
      rest() = Return(result *:: next)
      fill(next)
    }
  }
}
val rest = new Promise[Spool[Int]]
fill(rest)
firstElem *:: rest

explicitly (ie: {{import Spool.{*::, **:: }}}

def fill(rest: Promise[Spool[Int]]) {
  asyncProcess foreach { result =>
    if (result.last) {
      rest() = Return(result **:: Spool.empty)
    } else {
      val next = new Promise[Spool[Int]]
      rest() = Return(result *:: next)
      fill(next)
    }
  }
}
val rest = new Promise[Spool[Int]]
fill(rest)
firstElem *:: rest