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ListWrapper.scala
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ListWrapper.scala
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/*
* Copyright (c) 2015 Typelevel
*
* Permission is hereby granted, free of charge, to any person obtaining a copy of
* this software and associated documentation files (the "Software"), to deal in
* the Software without restriction, including without limitation the rights to
* use, copy, modify, merge, publish, distribute, sublicense, and/or sell copies of
* the Software, and to permit persons to whom the Software is furnished to do so,
* subject to the following conditions:
*
* The above copyright notice and this permission notice shall be included in all
* copies or substantial portions of the Software.
*
* THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
* IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY, FITNESS
* FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR
* COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER
* IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN
* CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.
*/
package cats
package tests
import org.scalacheck.{Arbitrary, Cogen}
import org.scalacheck.Arbitrary.arbitrary
/**
* This data type exists purely for testing.
*
* The problem this type solves is to assist in picking up type class
* instances that have more general constraints.
*
* For instance, OneAnd[*, F[_]] has a Monad instance if F[_] does too.
* By extension, it has an Applicative instance, since Applicative is
* a superclass of Monad.
*
* However, if F[_] doesn't have a Monad instance but does have an
* Applicative instance (e.g. Validated), you can still get an
* Applicative instance for OneAnd[*, F[_]]. These two instances
* are different however, and it is a good idea to test to make sure
* all "variants" of the instances are lawful.
*
* By providing this data type, we can have implicit search pick up
* a specific type class instance by asking for it explicitly in a block.
* Note that ListWrapper has no type class instances in implicit scope,
* save for ones related to testing (e.g. Eq, Arbitrary, Cogen).
*
* {{{
* {
* implicit val functor: Functor[ListWrapper] = ListWrapper.functor
* checkAll(..., ...)
* }
* }}}
*/
final case class ListWrapper[A](list: List[A]) extends AnyVal
object ListWrapper {
def order[A: Order]: Order[ListWrapper[A]] = Order.by(_.list)
def partialOrder[A: PartialOrder]: PartialOrder[ListWrapper[A]] = PartialOrder.by(_.list)
def eqv[A: Eq]: Eq[ListWrapper[A]] = Eq.by(_.list)
def hash[A: Hash]: Hash[ListWrapper[A]] = Hash.by(_.list)
val traverse: Traverse[ListWrapper] = {
val F = Traverse[List]
new Traverse[ListWrapper] {
def foldLeft[A, B](fa: ListWrapper[A], b: B)(f: (B, A) => B): B =
F.foldLeft(fa.list, b)(f)
def foldRight[A, B](fa: ListWrapper[A], lb: Eval[B])(f: (A, Eval[B]) => Eval[B]): Eval[B] =
F.foldRight(fa.list, lb)(f)
def traverse[G[_], A, B](fa: ListWrapper[A])(f: A => G[B])(implicit G0: Applicative[G]): G[ListWrapper[B]] =
G0.map(F.traverse(fa.list)(f))(ListWrapper.apply)
}
}
val traverseFilter: TraverseFilter[ListWrapper] = {
val F = TraverseFilter[List]
new TraverseFilter[ListWrapper] {
def traverse = ListWrapper.traverse
def traverseFilter[G[_], A, B](
fa: ListWrapper[A]
)(f: A => G[Option[B]])(implicit G: Applicative[G]): G[ListWrapper[B]] =
G.map(F.traverseFilter(fa.list)(f))(ListWrapper.apply)
}
}
val functorFilter: FunctorFilter[ListWrapper] = {
val F = FunctorFilter[List]
new FunctorFilter[ListWrapper] {
def functor = ListWrapper.functor
def mapFilter[A, B](fa: ListWrapper[A])(f: A => Option[B]): ListWrapper[B] =
ListWrapper(F.mapFilter(fa.list)(f))
}
}
val foldable: Foldable[ListWrapper] = traverse
val functor: Functor[ListWrapper] = traverse
val invariantSemigroupal: InvariantSemigroupal[ListWrapper] = new InvariantSemigroupal[ListWrapper] {
def product[A, B](fa: ListWrapper[A], fb: ListWrapper[B]): ListWrapper[(A, B)] =
ListWrapper(fa.list.flatMap(a => fb.list.map(b => (a, b))))
def imap[A, B](fa: ListWrapper[A])(f: A => B)(g: B => A) =
ListWrapper(fa.list.map(f))
}
val invariant: Invariant[ListWrapper] = invariantSemigroupal
val semigroupK: SemigroupK[ListWrapper] =
new SemigroupK[ListWrapper] {
def combineK[A](x: ListWrapper[A], y: ListWrapper[A]): ListWrapper[A] =
ListWrapper(SemigroupK[List].combineK(x.list, y.list))
}
def semigroup[A]: Semigroup[ListWrapper[A]] = semigroupK.algebra[A]
val alternative: Alternative[ListWrapper] = {
val M = Alternative[List]
new Alternative[ListWrapper] {
def pure[A](x: A): ListWrapper[A] = ListWrapper(M.pure(x))
def ap[A, B](f: ListWrapper[A => B])(fa: ListWrapper[A]): ListWrapper[B] =
ListWrapper(M.ap(f.list)(fa.list))
def empty[A]: ListWrapper[A] = ListWrapper(M.empty[A])
def combineK[A](x: ListWrapper[A], y: ListWrapper[A]): ListWrapper[A] =
ListWrapper(M.combineK(x.list, y.list))
}
}
def nonEmptyAlternative: NonEmptyAlternative[ListWrapper] = alternative
val monad: Monad[ListWrapper] = new Monad[ListWrapper] {
val M = Monad[List]
def pure[A](x: A): ListWrapper[A] = ListWrapper(x :: Nil)
def flatMap[A, B](fa: ListWrapper[A])(f: (A) => ListWrapper[B]): ListWrapper[B] =
ListWrapper(fa.list.flatMap(f(_).list))
def tailRecM[A, B](a: A)(f: (A) => ListWrapper[Either[A, B]]): ListWrapper[B] =
ListWrapper(M.tailRecM(a)(f(_).list))
}
val flatMap: FlatMap[ListWrapper] = monad
val applicative: Applicative[ListWrapper] = alternative
/**
* apply is taken due to ListWrapper being a case class
*/
val applyInstance: Apply[ListWrapper] = alternative
def monoidK: MonoidK[ListWrapper] = alternative
def monoid[A]: Monoid[ListWrapper[A]] = alternative.algebra[A]
implicit def listWrapperArbitrary[A: Arbitrary]: Arbitrary[ListWrapper[A]] =
Arbitrary(arbitrary[List[A]].map(ListWrapper.apply))
implicit def listWrapperCogen[A: Cogen]: Cogen[ListWrapper[A]] =
Cogen[List[A]].contramap(_.list)
implicit def listWrapperEq[A: Eq]: Eq[ListWrapper[A]] =
Eq.by(_.list)
}