Sanshiro Yoshida halcat0x15a

一つの型に対して2つのインスタンスを提供する

コンパニオンオブジェクトの同一階層に複数のimplicit valueを定義した場合

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	object GADTs {

	sealed trait Data1[A]
	case class Constructor1() extends Data1[Int]

	sealed trait Data2 { type T }
	case class Constructor2() extends Data2 { type T = Int }

	def f1[A](data: Data1[A]): A = data match { case Constructor1() => 0 }
	//def f2[A](data: Data2 { type T = A }): A = data match { case Constructor2() => 0 }

	import scala.annotation.tailrec

	sealed abstract class Var {

	def walk(subst: Subst): Var = {
	@tailrec
	def go(v: Var, stack: List[Var], acc: Option[Var]): Var =
	v match {
	case Unbound(k) =>
	subst.get(k) match {

	import scala.annotation.tailrec

	sealed abstract class Queue[U <: Union, -A, +B] {

	def apply(a: A): Free[U, B] = {
	@tailrec
	def go(tpe: { type T })(arrows: Queue[U, tpe.T, B], value: tpe.T): Free[U, B] =
	arrows.view match {
	case One(f) => f(value)
	case cons@Cons() =>

	package kits.free

	import scala.annotation.tailrec

	sealed abstract class Queue[R[_], -A, +B] {

	def :+[C](f: B => Free[R, C]): Queue[R, A, C] = new Node(this, new Leaf(f))

	def ++[C](that: Queue[R, B, C]): Queue[R, A, C] = new Node(this, that)

	import scala.annotation.tailrec

	sealed abstract class Queue[F[_], A, B] {

	def :+[C](f: B => F[C]): Queue[F, A, C] =
	new Node(this, new Leaf(f))

	def ++[C](that: Queue[F, B, C]): Queue[F, A, C] =
	new Node(this, that)

	@tailrec
	def go[F[_], A, B](arg: (Queue[F, A, T], Queue[F, T, B]) forSome { type T }): View[F, A, B] = {
	arg match {
	case (Leaf(v), y) => new Cons(v, y)
	case (Node(l, r), y) => go[F, A, B](l, Node(r, y))
	}
	}