Scala example source code file (MVarUsage.scala)

This example Scala source code file (MVarUsage.scala) is included in the alvinalexander.com "Java Source Code Warehouse" project. The intent of this project is to help you "Learn Scala by Example" ^TM.

Learn more about this Scala project at its project page.

Java - Scala tags/keywords

app, mvar, mvarusage, strategy

The MVarUsage.scala Scala example source code

package scalaz
package example
package concurrent

import scalaz._
import effect._
import IO._
import concurrent._
import MVar._
import std.anyVal._
import syntax.equal._

object MVarUsage extends App {
  def forkIO(f: => IO[Unit])(implicit s: Strategy): IO[Unit] = IO { s(f.unsafePerformIO); () }

  def out() {
    def calc(mvar: MVar[Int]): IO[Unit] = mvar.put(42)

    val io =
      for {
        mvar <- newEmptyMVar[Int]
        _ <- forkIO(calc(mvar))
        a <- mvar.take
      } yield a
    assert(io.unsafePerformIO === 42)
  }

  def inout() {
    def calc(in: MVar[Int], out: MVar[Int]): IO[Unit] =
      for {
        a <- in.take
        b <- in.take
        _ <- out.put(a * b)
      } yield ()

    val io =
      for {
        in  <- newMVar(6)
        out <- newEmptyMVar[Int]
        _   <- forkIO(calc(in, out))
        _   <- in.put(7)
        a   <- out.take
      } yield a
    assert(io.unsafePerformIO === 42)
  }

  def pingpong() {
    def pong(c: MVar[String], p: MVar[String]) =
      for {
        _ <- c.take flatMap (s => putStrLn("c: " + s))
        _ <- p.put("pong")
        _ <- c.take flatMap (s => putStrLn("c: " + s))
        _ <- p.put("pong")
      } yield ()

    def io =
      for {
        c <- newMVar("ping")
        p <- newEmptyMVar[String]
        _ <- forkIO(pong(c, p))
        _ <- p.take flatMap (s => putStrLn("p: " + s))
        _ <- c.put("ping")
        _ <- p.take flatMap (s => putStrLn("p: " + s))
      } yield ()
    io.unsafePerformIO
  }

  //out()
  //inout()
  pingpong()
}