ContT

cats.data.ContT

See theContT companion class

object ContT

Attributes

Companion: class
Source: ContT.scala
Graph
Supertypes: trait Sum

trait Mirror

class Object

trait Matchable

class Any
Self type: ContT.type

Members list

Type members

Inherited types

The names of the product elements

Attributes

Inherited from:: Mirror
Source: Mirror.scala

The name of the type

Attributes

Inherited from:: Mirror
Source: Mirror.scala

Value members

Concrete methods

Build a computation that makes use of a callback, also known as a continuation.

Example:

ContT.apply { callback =>
  for {
    a <- doFirstThing()
    b <- doSecondThing(a)
    c <- callback(b)
    d <- doFourthThing(c)
  } yield d
}

Attributes

Source: ContT.scala

Attributes

Source: ContT.scala

Similar to pure but evaluation of the argument is deferred.

This is useful for building a computation which calls its continuation as the final step. Instead of writing:

ContT.apply { cb =>
  val x = foo()
  val y = bar(x)
  val z = baz(y)
  cb(z)
}

you can write:

ContT.defer {
  val x = foo()
  val y = bar(x)
  baz(y)
}

Attributes

Source: ContT.scala

Similar to apply but evaluation of the argument is deferred.

Attributes

Source: ContT.scala

Lifts the M[B] into an ContT[M, A, B].

scala> import cats._, data._,  implicits._
scala> val a: EitherT[Eval, String, Int] = 1.pure[EitherT[Eval, String, *]]
scala> val c: cats.data.ContT[EitherT[Eval, String, *], Int, Int] = ContT.liftF(a)
scala> c.run(EitherT.rightT(_)).value.value
res0: Either[String, Int] = Right(1)
scala> c.run(_ => EitherT.leftT("a")).value.value
res1: Either[String, Int] = Left(a)

Attributes

Source: ContT.scala

Same as liftF, but expressed as a FunctionK for use with mapK

scala> import cats._, data._
scala> trait Foo[F[_]] { def bar: F[Int] }
scala> def mapK[F[_], G[_]](fooF: Foo[F])(f: F ~> G): Foo[G] = new Foo[G] { def bar: G[Int] = f(fooF.bar) }
scala> val eitherTFoo = new Foo[EitherT[Eval, String, *]] { def bar = EitherT.rightT(1) }
scala> val contTFoo: Foo[ContT[EitherT[Eval, String, *], Int, *]] = mapK(eitherTFoo)(ContT.liftK)
scala> contTFoo.bar.run(EitherT.rightT(_)).value.value
res0: Either[String, Int] = Right(1)