smithy4s.codegen.internals.recursion.scala Maven / Gradle / Ivy
/*
* Copyright 2021-2024 Disney Streaming
*
* Licensed under the Tomorrow Open Source Technology License, Version 1.0 (the "License");
* you may not use this file except in compliance with the License.
* You may obtain a copy of the License at
*
* https://disneystreaming.github.io/TOST-1.0.txt
*
* 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 smithy4s.codegen
package internals
import cats.Functor
import cats.Monad
import cats.Traverse
import cats.syntax.all._
import cats.~>
private[internals] case class Fix[F[_]](unfix: F[Fix[F]])
/**
* This package contains recursion-scheme implementations.
* Because of the concision and the fact that we need a small subset of them,
* we re-implement them as opposed to depending on a library.
*
* See libraries that offer larger sets of recursion-schemes (and docs) :
* * Droste https://index.scala-lang.org/higherkindness/droste
* * Matryoshka https://index.scala-lang.org/precog/matryoshka
*
*/
private[internals] object recursion {
def hylo[F[_]: Functor, A, B](unfold: A => F[A], fold: F[B] => B)(a: A): B =
fold(unfold(a).map(hylo(unfold, fold)))
def hyloM[M[_]: Monad, F[_]: Traverse, A, B](
unfold: A => M[F[A]],
fold: F[B] => M[B]
)(a: A): M[B] = {
type MF[T] = M[F[T]] // composition of M and F
implicit val MF: Functor[MF] = Functor[M].compose(Functor[F])
val F = Traverse[F]
def foldM(mfmb: M[F[M[B]]]): M[B] = for {
fmb <- mfmb
fb <- F.sequence[M, B](fmb)
f <- fold(fb)
} yield f
hylo[MF, A, M[B]](unfold, foldM)(a)
}
def cata[F[_]: Functor, B](fold: F[B] => B)(tree: Fix[F]): B =
hylo[F, Fix[F], B](_.unfix, fold)(tree)
def ana[F[_]: Functor, A](unfold: A => F[A])(a: A): Fix[F] =
hylo[F, A, Fix[F]](unfold, Fix(_))(a)
def anaM[M[_]: Monad, F[_]: Traverse, A](unfold: A => M[F[A]])(
a: A
): M[Fix[F]] =
hyloM[M, F, A, Fix[F]](unfold, x => Monad[M].pure(Fix(x)))(a)
def preprocess[F[_]: Functor](nt: F ~> F)(tree: Fix[F]): Fix[F] =
cata[F, Fix[F]](ff => Fix(nt(ff)))(tree)
}