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amitayh/io-monad.scala

Created February 5, 2017 07:15
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io-monad.scala
import scala.io.StdIn.readLine
trait IO[+A] {
def run(): A
def flatMap[B](f: A => IO[B]): IO[B] = IO(f(run()).run())
def map[B](f: A => B): IO[B] = flatMap(a => IO(f(a)))
}
object IO {
def apply[A](a: => A): IO[A] = new IO[A] {
def run(): A = a
}
}
def PrintLn(x: String): IO[Unit] = IO(println(x))
def ReadLn: IO[String] = IO(readLine())
val prog = for {
name <- ReadLn
_ <- PrintLn(s"Hello, $name!")
} yield ()
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