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FreeApply.scala
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FreeApply.scala
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/*
* Copyright 2023 Valdemar Grange
*
* Licensed under the Apache License, Version 2.0 (the "License");
* you may not use this file except in compliance with the License.
* You may obtain a copy of the License at
*
* http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
* See the License for the specific language governing permissions and
* limitations under the License.
*/
package gql.std
import cats._
import cats.implicits._
import cats.data._
import scala.annotation.nowarn
/** FreeApply is a Free Applicative, but witout pure. It has an Apply instance.
*/
sealed abstract class FreeApply[F[_], +A] extends Product with Serializable {
def foldMap[G[_], B >: A](fk: F ~> G)(implicit G: Apply[G]): G[B] =
FreeApply.foldMap[F, G, B](this)(fk)
// Very cool, we can do non-empty algebras with semigroup with the cool Const Semigroup => Apply[Cost] typeclass impl
def analyze[M: Semigroup](fk: F ~> λ[α => M]): M =
foldMap[Const[M, *], A](new (F ~> Const[M, *]) {
def apply[B](fa: F[B]): Const[M, B] = Const(fk(fa))
}).getConst
@nowarn
def analyze_[M: Semigroup](fold: F[Any] => M): M =
foldMap[Const[M, *], A](new (F ~> Const[M, *]) {
def apply[A](fa: F[A]): Const[M, A] = Const(fold(fa.asInstanceOf[F[Any]]))
}).getConst
@nowarn
def enumerate: NonEmptyChain[F[Any]] =
analyze_(fa => NonEmptyChain.one(fa))
}
object FreeApply {
def foldMap[F[_], G[_], A](fa: FreeApply[F, A])(fk: F ~> G)(implicit G: Apply[G]): G[A] = {
@nowarn
def go[B](fa: FreeApply[F, B]): Eval[G[B]] = Eval.defer {
fa match {
case Lift(fa) => Eval.now(G.map(fk(fa))(x => x))
case fmap: Fmap[F, a, B] => go(fmap.fa).map(G.map(_)(fmap.f))
case ap: Ap[F, a, B] => (go(ap.ff), go(ap.fa)).mapN((gf, ga) => G.ap(gf)(ga))
}
}
go(fa).value
}
final case class Ap[F[_], A, B](ff: FreeApply[F, A => B], fa: FreeApply[F, A]) extends FreeApply[F, B]
final case class Lift[F[_], A](fa: F[A]) extends FreeApply[F, A]
// Allows O(1) fmap
final case class Fmap[F[_], A, B](fa: FreeApply[F, A], f: A => B) extends FreeApply[F, B]
def lift[F[_], A](fa: F[A]): FreeApply[F, A] = Lift(fa)
implicit def freeApply[F[_]]: Apply[FreeApply[F, *]] = {
type G[A] = FreeApply[F, A]
new Apply[G] {
override def map[A, B](fa: G[A])(f: A => B): G[B] = Fmap(fa, f)
override def ap[A, B](ff: G[A => B])(fa: G[A]): G[B] = Ap(ff, fa)
}
}
}