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/* __ *\
** ________ ___ / / ___ Scala API **
** / __/ __// _ | / / / _ | (c) 2005-2013, LAMP/EPFL **
** __\ \/ /__/ __ |/ /__/ __ | http://scala-lang.org/ **
** /____/\___/_/ |_/____/_/ | | **
** |/ **
\* */
package scala
/** This object contains utility methods to build responders.
*
* @author Martin Odersky
* @author Burak Emir
* @version 1.0
*
* @see class Responder
* @since 2.1
*/
object Responder {
/** Creates a responder that answer continuations with the constant `a`.
*/
def constant[A](x: A) = new Responder[A] {
def respond(k: A => Unit) = k(x)
}
/** Executes `x` and returns `'''true'''`, useful as syntactic
* convenience in for comprehensions.
*/
def exec[A](x: => Unit): Boolean = { x; true }
/** Runs a responder, returning an optional result.
*/
def run[A](r: Responder[A]): Option[A] = {
var result: Option[A] = None
r.foreach(x => result = Some(x))
result
}
def loop[A](r: Responder[Unit]): Responder[Nothing] =
for (_ <- r; y <- loop(r)) yield y
def loopWhile[A](cond: => Boolean)(r: Responder[Unit]): Responder[Unit] =
if (cond) for (_ <- r; y <- loopWhile(cond)(r)) yield y
else constant(())
}
/** Instances of responder are the building blocks of small programs
* written in continuation passing style. By using responder classes
* in for comprehensions, one can embed domain-specific languages in
* Scala while giving the impression that programs in these DSLs are
* written in direct style.
*
* @author Martin Odersky
* @author Burak Emir
* @version 1.0
* @since 2.1
*/
abstract class Responder[+A] extends Serializable {
def respond(k: A => Unit): Unit
def foreach(k: A => Unit) { respond(k) }
def map[B](f: A => B) = new Responder[B] {
def respond(k: B => Unit) {
Responder.this.respond(x => k(f(x)))
}
}
def flatMap[B](f: A => Responder[B]) = new Responder[B] {
def respond(k: B => Unit) {
Responder.this.respond(x => f(x).respond(k))
}
}
def filter(p: A => Boolean) = new Responder[A] {
def respond(k: A => Unit) {
Responder.this.respond(x => if (p(x)) k(x) else ())
}
}
override def toString = "Responder"
}
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