fs2.data.pattern.Selector.scala Maven / Gradle / Ivy
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/*
* Copyright 2024 fs2-data Project
*
* 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 fs2.data.pattern
import cats.Show
import cats.syntax.all._
import scala.annotation.tailrec
/** A [[Selector]] represents the part of the matched input that is
* under scrutinee during the pattern match.
*/
sealed trait Selector[Expr, Tag] {
def tags: List[Either[(Tag, Int), Expr]] = {
@tailrec
def loop(sel: Selector[Expr, Tag], acc: List[Either[(Tag, Int), Expr]]): List[Either[(Tag, Int), Expr]] =
sel match {
case Selector.Root() => acc
case Selector.Cons(parent, tag, arg) => loop(parent, (tag, arg).asLeft :: acc)
case Selector.Guard(parent, guard) => loop(parent, guard.asRight :: acc)
}
loop(this, Nil)
}
}
object Selector {
case class Root[Expr, Tag]() extends Selector[Expr, Tag]
case class Cons[Expr, Tag](sel: Selector[Expr, Tag], tag: Tag, n: Int) extends Selector[Expr, Tag]
case class Guard[Expr, Tag](sel: Selector[Expr, Tag], expr: Expr) extends Selector[Expr, Tag]
implicit def show[E: Show, T: Show]: Show[Selector[E, T]] = _ match {
case Root() => "$"
case Cons(sel, tag, n) => show"$sel.$tag.$n"
case Guard(sel, expr) => show"$sel if $expr"
}
}