
Scala example source code file (Monad.scala)
The Monad.scala Scala example source codepackage scalaz //// /** * Monad, an [[scalaz.Applicative]] that also supports [[scalaz.Bind]], * circumscribed by the monad laws. * * @see [[scalaz.Monad.MonadLaw]] */ //// trait Monad[F[_]] extends Applicative[F] with Bind[F] { self => //// override def map[A,B](fa: F[A])(f: A => B) = bind(fa)(a => point(f(a))) /** * Execute an action repeatedly as long as the given `Boolean` expression * returns `true`. The condition is evalated before the loop body. * Collects the results into an arbitrary `MonadPlus` value, such as a `List`. */ def whileM[G[_], A](p: F[Boolean], body: => F[A])(implicit G: MonadPlus[G]): F[G[A]] = { val f = Need(body) ifM(p, bind(f.value)(x => map(whileM(p, f.value))(xs => G.plus(G.point(x), xs))), point(G.empty)) } /** * Execute an action repeatedly as long as the given `Boolean` expression * returns `true`. The condition is evaluated before the loop body. * Discards results. */ def whileM_[A](p: F[Boolean], body: => F[A]): F[Unit] = { val f = Need(body) ifM(p, bind(f.value)(_ => whileM_(p, f.value)), point(())) } /** * Execute an action repeatedly until the `Boolean` condition returns `true`. * The condition is evaluated after the loop body. Collects results into an * arbitrary `MonadPlus` value, such as a `List`. */ def untilM[G[_], A](f: F[A], cond: => F[Boolean])(implicit G: MonadPlus[G]): F[G[A]] = { val p = Need(cond) bind(f)(x => map(whileM(map(p.value)(!_), f))(xs => G.plus(G.point(x), xs))) } /** * Execute an action repeatedly until the `Boolean` condition returns `true`. * The condition is evaluated after the loop body. Discards results. */ def untilM_[A](f: F[A], cond: => F[Boolean]): F[Unit] = { val p = Need(cond) bind(f)(_ => whileM_(map(p.value)(!_), f)) } /** * Execute an action repeatedly until its result fails to satisfy the given predicate * and return that result, discarding all others. */ def iterateWhile[A](f: F[A])(p: A => Boolean): F[A] = bind(f)(y => if (p(y)) iterateWhile(f)(p) else point(y)) /** * Execute an action repeatedly until its result satisfies the given predicate * and return that result, discarding all others. */ def iterateUntil[A](f: F[A])(p: A => Boolean): F[A] = bind(f)(y => if (p(y)) point(y) else iterateUntil(f)(p)) /**The product of Monad `F` and `G`, `[x](F[x], G[x]])`, is a Monad */ def product[G[_]](implicit G0: Monad[G]): Monad[λ[α => (F[α], G[α])]] = new ProductMonad[F, G] { def F = self def G = G0 } trait MonadLaw extends ApplicativeLaw with BindLaw { /** Lifted `point` is a noop. */ def rightIdentity[A](a: F[A])(implicit FA: Equal[F[A]]): Boolean = FA.equal(bind(a)(point(_: A)), a) /** Lifted `f` applied to pure `a` is just `f(a)`. */ def leftIdentity[A, B](a: A, f: A => F[B])(implicit FB: Equal[F[B]]): Boolean = FB.equal(bind(point(a))(f), f(a)) } def monadLaw = new MonadLaw {} //// val monadSyntax = new scalaz.syntax.MonadSyntax[F] { def F = Monad.this } } object Monad { @inline def apply[F[_]](implicit F: Monad[F]): Monad[F] = F //// implicit def monadMTMAB[MT[_[_], _], MAB[_, _], A](implicit t: MonadTrans[MT], m: Monad[MAB[A, ?]]): Monad[MT[MAB[A, ?], ?]] = t.apply[MAB[A, ?]] //// } Other Scala examples (source code examples)Here is a short list of links related to this Scala Monad.scala source code file: 
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