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A purely functional XML library

There is a newer version: 0.0.19

package cats.xml.modifier

import cats.Monoid

/** Create a modified copy of input 'XmlNode'
  */
trait Modifier[T] { $this =>

  /** Apply a transformation to the input value `T`
    * @param value
    *   Changes subject
    * @return
    *   an `Either[ModifierFailure, T]` that represent the modification result. `Left` failed,
    *   `Right` succeed
    */
  def apply(value: T): Modifier.Result[T]

  /** Like `flatMap` but doesn't allow type transformation. Just combines two `Modifier` for the
    * same type `T`.
    * @param that
    *   Modifier instance to combine with this
    * @return
    *   A new `Modifier` which apply this changes first and then, if it succeed apply `that`
    *   Modifier changes.
    */
  def combine(that: Modifier[T]): Modifier[T] =
    (value: T) => $this(value).flatMap(that(_))
}

object Modifier extends ModifierInstances {

  import cats.implicits.*

  type Result[+T] = Either[ModifierFailure, T]

  def apply[T](
    f: T => Modifier.Result[T]
  ): Modifier[T] = (input: T) => f(input)

  def id[T]: Modifier[T] =
    Modifier(_.asRight)

  def pure[T](value: T): Modifier[T] =
    const(value.asRight)

  def const[T](
    result: => Modifier.Result[T]
  ): Modifier[T] =
    Modifier(_ => result)

  def failed[T](
    result: => ModifierFailure
  ): Modifier[T] =
    const(result.asLeft)
}

sealed trait ModifierInstances {

  implicit def monoidForModifier[T]: Monoid[Modifier[T]] = new Monoid[Modifier[T]] {
    override def empty: Modifier[T]                                   = Modifier.id[T]
    override def combine(x: Modifier[T], y: Modifier[T]): Modifier[T] = x.combine(y)
  }
}