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 {
   
   final 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 Product with Serializable

   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 values synchronously via returning now, or promise to invoke a callback via returning later.

3.  type Canceler = IO[Nothing, _]
4.  sealed trait Chunk[+A] extends AnyRef

   A Chunk[A] represents a chunk of values of type A.

   A Chunk[A] represents a chunk of values of type A. Chunks are designed are usually backed by arrays, but expose a purely functional, safe interface to the underlying elements, and they become lazy on operations that would be costly with arrays, such as repeated concatenation.

5.  trait Clock extends Serializable
6.  trait EitherCompat extends AnyRef
7.  sealed abstract class Exit[+E, +A] extends Product with Serializable

   An Exit[E, A] describes the result of executing an IO value.

   An Exit[E, A] describes the result of executing an IO value. The result is either succeeded with a value A, or failed with a Cause[E].

8.  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

9.  final case class FiberFailure(cause: Cause[Any]) extends Throwable with Product with Serializable
10.  type FiberId = Long
11.  final class FiberLocal[A] extends Serializable

    A container for fiber-local storage.

    A container for fiber-local storage. It is the pure equivalent to Java's ThreadLocal on a fiber architecture.

12.  sealed abstract class FunctionIO[+E, -A, +B] extends Serializable

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

    A FunctionIO[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, FunctionIO extends this function type, and can be used in the same way.

    The main advantage to using FunctionIO is that it provides you a means of importing an impure function A => B into FunctionIO[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 FunctionIO[E, A, B]. Such functions cannot be optimized, but will be handled correctly and can work in conjunction with optimized (fused) FunctionIO.

    Those interested in learning more about modeling effects with FunctionIO 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 FunctionIO, 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 FunctionIO:

    val readLine = FunctionIO.impureVoid((_ : Unit) => scala.Console.readLine())
    val printLine = FunctionIO.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 >>> FunctionIO.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 FunctionIO program is faster because it is able to perform fusion of effectful functions.

13.  sealed abstract class IO[+E, +A] extends Serializable

    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.

14.  final case class Managed[+E, +R](reserve: IO[E, Reservation[E, R]]) extends Product with Serializable

    A Managed[E, R] is a managed resource of type R, which may be used by invoking the use method of the resource.

    A Managed[E, R] is a managed resource of type R, which may be used by invoking the use method of the resource. The resource will be automatically acquired before the resource is used, and automatically released after the resource is used.

    Resources do not survive the scope of use, meaning that if you attempt to capture the resource, leak it from use, and then use it after the resource has been consumed, the resource will not be valid anymore and may fail with some checked error, as per the type of the functions provided by the resource.

15.  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

16.  class Queue[A] extends Serializable

    A Queue[A] is a lightweight, asynchronous queue for values of type A.

17.  trait RTS extends AnyRef
18.  final class Ref[A] extends AnyVal with Serializable

    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.update(_ + 3)
      _   <- putStrLn("Value = " + v) // Value = 5
    } yield ()

19.  final class RefM[A] extends Serializable

    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 effectful operations, which make it useful as a reasonably efficient (if low-level) concurrency primitive.

    Unlike Ref, RefM allows effects in atomic operations, which makes the structure slower but more powerful than Ref.

    for {
      ref <- RefM(2)
      v   <- ref.update(_ + putStrLn("Hello World!").attempt.void *> IO.succeed(3))
      _   <- putStrLn("Value = " + v) // Value = 5
    } yield ()

20.  trait Schedule[-A, +B] extends Serializable

    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 continue or halt. 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.

    Schedule[A, B] forms a profunctor on [A, B], an applicative functor on B, and a monoid, allowing rich composition of different schedules.

21.  final class Semaphore extends Serializable
22.  trait ZIO[F[_, _]] extends AnyRef

    A type class that allows people to use ZIO-specific code with other effect monads, so long as they can lift an arbitrary IO computation into their type.

    A type class that allows people to use ZIO-specific code with other effect monads, so long as they can lift an arbitrary IO computation into their type. See the interop modules for instances of this type class for other effect types.