zio

Type Members

1. trait App extends RTS

   

   The entry point for a purely-functional application on the JVM.

   The entry point for a purely-functional application on the JVM.

   import java.io.IOException
   import scalaz.zio.{App, IO}
   import scalaz.zio.console._
   
   object MyApp extends App {
   
     def run(args: List[String]): IO[Nothing, ExitStatus] =
       myAppLogic.attempt.map(_.fold(_ => 1, _ => 0)).map(ExitStatus.ExitNow(_))
   
     def myAppLogic: IO[IOException, Unit] =
       for {
         _ <- putStrLn("Hello! What is your name?")
         n <- getStrLn
         _ <- putStrLn("Hello, " + n + ", good to meet you!")
       } yield ()
   }

2. sealed abstract class Async[+E, +A] extends AnyRef

   

   The Async class describes the return value of an asynchronous effect that is imported into an IO value.

   The Async class describes the return value of an asynchronous effect that is imported into an IO value.

   Asynchronous effects can return later, which represents an uninterruptible asynchronous action, now which represents a synchronously computed value, maybeLater, which represents an interruptible asynchronous action or maybeLaterIO which represents an interruptible asynchronous action where the canceler has the form Throwable => IO[Nothing, Unit]

3. type Callback[E, A] = (ExitResult[E, A]) ⇒ Unit

   

4. type Canceler = () ⇒ Unit

   

5. sealed trait ExitResult[+E, +A] extends AnyRef

   

   A description of the result of executing an IO value.

   A description of the result of executing an IO value. The result is either completed with a value, failed because of an uncaught E, or terminated due to interruption or runtime error.

6. trait Fiber[+E, +A] extends AnyRef

   

   A fiber is a lightweight thread of execution that never consumes more than a whole thread (but may consume much less, depending on contention).

   A fiber is a lightweight thread of execution that never consumes more than a whole thread (but may consume much less, depending on contention). Fibers are spawned by forking IO actions, which, conceptually at least, runs them concurrently with the parent IO action.

   Fibers can be joined, yielding their result other fibers, or interrupted, which terminates the fiber with a runtime error.

   Fork-Join Identity: fork >=> join = id

   for {
     fiber1 <- io1.fork
     fiber2 <- io2.fork
     _      <- fiber1.interrupt(e)
     a      <- fiber2.join
   } yield a

7. sealed abstract class IO[+E, +A] extends AnyRef

   

   An IO[E, A] ("Eye-Oh of Eeh Aye") is an immutable data structure that describes an effectful action that may fail with an E, run forever, or produce a single A at some point in the future.

   An IO[E, A] ("Eye-Oh of Eeh Aye") is an immutable data structure that describes an effectful action that may fail with an E, run forever, or produce a single A at some point in the future.

   Conceptually, this structure is equivalent to EitherT[F, E, A] for some infallible effect monad F, but because monad transformers perform poorly in Scala, this structure bakes in the EitherT without runtime overhead.

   IO values are ordinary immutable values, and may be used like any other values in purely functional code. Because IO values just *describe* effects, which must be interpreted by a separate runtime system, they are entirely pure and do not violate referential transparency.

   IO values can efficiently describe the following classes of effects:

   * **Pure Values** — IO.point * **Synchronous Effects** — IO.sync * **Asynchronous Effects** — IO.async * **Concurrent Effects** — io.fork * **Resource Effects** — io.bracket

   The concurrency model is based on *fibers*, a user-land lightweight thread, which permit cooperative multitasking, fine-grained interruption, and very high performance with large numbers of concurrently executing fibers.

   IO values compose with other IO values in a variety of ways to build complex, rich, interactive applications. See the methods on IO for more details about how to compose IO values.

   In order to integrate with Scala, IO values must be interpreted into the Scala runtime. This process of interpretation executes the effects described by a given immutable IO value. For more information on interpreting IO values, see the default interpreter in RTS or the safe main function in App.

8. sealed trait KleisliIO[+E, -A, +B] extends AnyRef

   

   A KleisliIO[E, A, B] is an effectful function from A to B, which might fail with an E.

   A KleisliIO[E, A, B] is an effectful function from A to B, which might fail with an E.

   This is the moral equivalent of A => IO[E, B], and, indeed, KleisliIO extends this function type, and can be used in the same way.

   The main advantage to using KleisliIO is that it provides you a means of importing an impure function A => B into KleisliIO[E, A, B], without actually wrapping the result of the function in an IO value.

   This allows the implementation to aggressively fuse operations on impure functions, which in turn can result in significantly higher-performance and far less heap utilization than equivalent approaches modeled with IO.

   The implementation allows you to lift functions from A => IO[E, B] into a KleisliIO[E, A, B]. Such functions cannot be optimized, but will be handled correctly and can work in conjunction with optimized (fused) KleisliIO.

   Those interested in learning more about modeling effects with KleisliIO are encouraged to read John Hughes paper on the subject: Generalizing Monads to Arrows (www.cse.chalmers.se/~rjmh/Papers/arrows.pdf). The implementation in this file contains many of the same combinators as Hughes implementation.

   A word of warning: while even very complex code can be expressed in KleisliIO, there is a point of diminishing return. If you find yourself using deeply nested tuples to propagate information forward, it may be no faster than using IO.

   Given the following two KleisliIO:

   val readLine = KleisliIO.impureVoid((_ : Unit) => scala.Console.readLine())
   val printLine = KleisliIO.impureVoid((line: String) => println(line))

   Then the following two programs are equivalent:

   // Program 1
   val program1: IO[Nothing, Unit] =
     for {
       name <- getStrLn
       _    <- putStrLn("Hello, " + name)
     } yield ())
   
   // Program 2
   val program2: IO[Nothing, Unit] = (readLine >>> KleisliIO.lift("Hello, " + _) >>> printLine)(())

   Similarly, the following two programs are equivalent:

   // Program 1
   val program1: IO[Nothing, Unit] =
     for {
       line1 <- getStrLn
       line2 <- getStrLn
       _     <- putStrLn("You wrote: " + line1 + ", " + line2)
     } yield ())
   
   // Program 2
   val program2: IO[Nothing, Unit] =
     (readLine.zipWith(readLine)("You wrote: " + _ + ", " + _) >>> printLine)(())

   In both of these examples, the KleisliIO program is faster because it is able to perform fusion of effectful functions.

9. final class Promise[E, A] extends AnyVal

   

   A promise represents an asynchronous variable that can be set exactly once, with the ability for an arbitrary number of fibers to suspend (by calling get) and automatically resume when the variable is set.

   A promise represents an asynchronous variable that can be set exactly once, with the ability for an arbitrary number of fibers to suspend (by calling get) and automatically resume when the variable is set.

   Promises can be used for building primitive actions whose completions require the coordinated action of multiple fibers, and for building higher-level concurrent or asynchronous structures.

   for {
     promise <- Promise.make[Nothing, Int]
     _       <- promise.complete(42).delay(1.second).fork
     value   <- promise.get // Resumes when forked fiber completes promise
   } yield value

10. type PureCanceler = () ⇒ IO[Nothing, Unit]

    

11. class Queue[A] extends AnyRef

    

     * A Queue is a lightweight, asynchronous queue.

     * A Queue is a lightweight, asynchronous queue. This implementation is  * naive, if functional, and could benefit from significant optimization.  *  * TODO:  *  * 1. Investigate using a faster option than Queue, because Queue has  *    O(n) length method.  * 2. Benchmark to see how slow this implementation is and if there are any  *    easy ways to improve performance.  

12. trait RTS extends AnyRef

    

    This trait provides a high-performance implementation of a runtime system for the IO monad on the JVM.

13. final class Ref[A] extends AnyVal

    

    A mutable atomic reference for the IO monad.

    A mutable atomic reference for the IO monad. This is the IO equivalent of a volatile var, augmented with atomic operations, which make it useful as a reasonably efficient (if low-level) concurrency primitive.

    for {
      ref <- Ref(2)
      v   <- ref.modify(_ + 3)
      _   <- putStrLn("Value = " + v.debug) // Value = 5
    } yield ()

14. trait Schedule[-A, +B] extends AnyRef

    

    Defines a stateful, possibly effectful, recurring schedule of actions.

    Defines a stateful, possibly effectful, recurring schedule of actions.

    A Schedule[A, B] consumes A values, and based on the inputs and the internal state, decides whether to recur or conclude. Every decision is accompanied by a (possibly zero) delay, and an output value of type B.

    Schedules compose in each of the following ways:

    1. Intersection, using the && operator, which requires that both schedules continue, using the longer of the two durations. 2. Union, using the || operator, which requires that only one schedule continues, using the shorter of the two durations. 3. Sequence, using the <||> operator, which runs the first schedule until it ends, and then switches over to the second schedule.

    Thanks to (1), Schedule[A, B] forms an applicative functor on the output value B, allowing rich composition of different schedules.

15. final class Semaphore extends AnyRef