
Scala example source code file (ContravariantCoyoneda.scala)
The ContravariantCoyoneda.scala Scala example source codepackage scalaz /** Decomposition of `fi.contramap(k)` into its components, as it is * frequently convenient to apply `k` separately from sorting or * whatever process with `fi`, even when `B` is unknown, which is * very common. * * This is isomorphic to `F` as long as `F` itself is a contravariant * functor. The homomorphism from `F[A]` to * `ContravariantCoyoneda[F,A]` exists even when `F` is not a * contravariant functor. * * See `ContravariantCoyonedaUsage.scala` in the scalaz source tree * for an interesting usage demonstration. * * As `ContravariantCoyoneda(o)(identity).unlift` = `o`, further * factoring can occur as follows, for free: * * {{{ * ContravariantCoyoneda(o contramap g)(f).unlift = * ContravariantCoyoneda(o)(g compose f).unlift * }}} * * @see [[http://hackage.haskell.org/package/kanextensions4.0.1/docs/DataFunctorContravariantCoyoneda.html]] */ sealed abstract class ContravariantCoyoneda[F[_], A] { /** The pivot between `fi` and `k`, usually existential. */ type I /** The underlying value. */ val fi: F[I] /** The transformer function, to be lifted into `F` by `run`. */ val k: A => I import ContravariantCoyoneda.{Aux, apply} /** Converts to `F[A]` given that `F` is a contravariant. */ final def run(implicit F: Contravariant[F]): F[A] = F.contramap(fi)(k) /** Alias for `run`. */ @inline final def unlift(implicit F: Contravariant[F]): F[A] = run /** Simple function composition. Allows map fusion without touching * the underlying `F`. */ final def contramap[B](f: B => A): Aux[F, B, I] = apply(fi)(k compose f) /** Natural transformation. */ final def trans[G[_]](f: F ~> G): Aux[G, A, I] = apply(f(fi))(k) } sealed abstract class ContravariantCoyonedaInstances { /** `ContravariantCoyoneda[F,_]` is a contravariant functor for any * `F`. */ implicit def contravariantCoyonedaContravariant[F[_]]: Contravariant[ContravariantCoyoneda[F, ?]] = new Contravariant[ContravariantCoyoneda[F, ?]] { def contramap[A, B](fa: ContravariantCoyoneda[F, A])(f: B => A) = fa contramap f } } object ContravariantCoyoneda extends ContravariantCoyonedaInstances { /** Lift the `I` type member to a parameter. It is usually more * convenient to use `Aux` than a structural type. */ type Aux[F[_], A, B] = ContravariantCoyoneda[F, A] {type I = B} /** See `by` method. */ final class By[F[_]] { @inline def apply[A, B](k: A => B)(implicit F: F[B]): Aux[F, A, B] = ContravariantCoyoneda(F)(k) } /** Partial application of type parameters to `apply`. It is often * more convenient to invoke `ContravariantCoyoneda.by[F]{x: X => * ...}` then `ContravariantCoyoneda[...](...){x: X => ...}`. */ @inline def by[F[_]]: By[F] = new By[F] /** Like `lift(fa).contramap(_k)`. */ def apply[F[_], A, B](fa: F[B])(_k: A => B): Aux[F, A, B] = new ContravariantCoyoneda[F, A]{ type I = B val k = _k val fi = fa } /** `F[A]` converts to `ContravariantCoyoneda[F,A]` for any `F`. */ def lift[F[_], A](fa: F[A]): ContravariantCoyoneda[F, A] = apply(fa)(identity[A]) import Isomorphism._ def iso[F[_]: Contravariant]: ContravariantCoyoneda[F, ?] <~> F = new IsoFunctorTemplate[ContravariantCoyoneda[F, ?], F] { def from[A](fa: F[A]) = lift(fa) def to[A](fa: ContravariantCoyoneda[F, A]) = fa.run } } Other Scala examples (source code examples)Here is a short list of links related to this Scala ContravariantCoyoneda.scala source code file: 
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