Scala example source code file (State.scala)

This example Scala source code file (State.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.

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Java - Scala tags/keywords

indexedstate, indexedstatefunctions, state, unit

The State.scala Scala example source code

package scalaz


trait IndexedStateFunctions {
  def constantIndexedState[S1, S2, A](a: A, s: => S2): IndexedState[S1, S2, A] =
    IndexedState((_: S1) => (s, a))

  def iPut[S1, S2](s: S2): IndexedState[S1, S2, Unit] = IndexedState(_ => (s, ()))

  def iModify[S1, S2](f: S1 => S2): IndexedState[S1, S2, Unit] = IndexedState(s => {
    val r = f(s);
    (r, ())
  })
}

trait StateFunctions extends IndexedStateFunctions {
  def constantState[S, A](a: A, s: => S): State[S, A] =
    State((_: S) => (s, a))

  def state[S, A](a: A): State[S, A] =
    State((_ : S, a))

  def init[S]: State[S, S] = State(s => (s, s))

  def get[S]: State[S, S] = init

  def gets[S, T](f: S => T): State[S, T] = State(s => (s, f(s)))

  def put[S](s: S): State[S, Unit] = State(_ => (s, ()))

  def modify[S](f: S => S): State[S, Unit] = State(s => {
    val r = f(s);
    (r, ())
  })
}