Add GeneralizedDescendant and GeneralizedSuccessor

core/src/main/scala/eyrie/instances/DescendantInstances.scala

@@ -6,27 +6,30 @@ import eyrie.ops._
 
 import scala.Function.const
 
+private[eyrie]
+trait GeneralizedDescendantInstances {
+  implicit def eyrieNonDescendantBasedInstance[A, L, R](
+    implicit
+    A: Subdivision[A, L, R],
+    L: NonDescendant[L],
+    R: NonDescendant[R]
+  ): NonDescendant[A] =
+    new NonDescendant[A] { }
+}
+
 private[eyrie]
 trait DescendantInstances {
-  implicit def eyrieDescendantBasedInstance[A, LA, RA, B](
+  implicit def eyrieDescendantBasedInstance[A, L, R, B](
     implicit
-    A: Subdivision[A, LA, RA],
-    LA: Descendant[LA, B],
-    RA: Descendant[RA, B]
+    A: Subdivision[A, L, R],
+    L: Descendant[L, B],
+    R: Descendant[R, B]
   ): Descendant[A, B] =
     new Descendant[A, B] {
       override
       def root: A => B =
-        A.subdivide(_).fold(LA.root, RA.root)
+        A.subdivide(_).fold(L.root, R.root)
     }
-
-  implicit def eyrieNonDescendantBasedInstance[A, LA, RA](
-    implicit
-    A: Subdivision[A, LA, RA],
-    LA: NonDescendant[LA],
-    RA: NonDescendant[RA]
-  ): NonDescendant[A] =
-    eyrieDescendantBasedInstance[A, LA, RA, Nothing]
 }
 
 private[eyrie]

core/src/main/scala/eyrie/instances/DiSuccessorInstances.scala

@@ -52,17 +52,17 @@ trait DiPotentialSuccessorInstances {
   implicit def eyriePotentialSuccessorBasedInstance[A, LA, RA, LB, RB, C](
     implicit
     A: Subdivision[A, LA, RA],
-    L: PotentialSuccessor[LA, LB, C],
-    R: PotentialSuccessor[RA, RB, C]
+    LA: PotentialSuccessor[LA, LB, C],
+    RB: PotentialSuccessor[RA, RB, C]
   ): DiPotentialSuccessor[A, LB, RB, C] =
     new DiPotentialSuccessor[A, LB, RB, C] {
       override
       def parentEitherOption: A => Option[Either[LB, RB]] =
-        A.subdivide(_).fold(L.parentOption >>> (_.map(_.asLeft)), R.parentOption >>> (_.map(_.asRight)))
+        A.subdivide(_).fold(LA.parentOption >>> (_.map(_.asLeft)), RB.parentOption >>> (_.map(_.asRight)))
 
       override
       def lastSegmentOption: A => Option[C] =
-        A.subdivide(_).fold(L.lastSegmentOption, R.lastSegmentOption)
+        A.subdivide(_).fold(LA.lastSegmentOption, RB.lastSegmentOption)
     }
 }
 

core/src/main/scala/eyrie/instances/SuccessorInstances.scala

@@ -4,9 +4,20 @@ import cats.instances.all._
 import cats.syntax.compose._
 import eyrie.ops._
 
+private[eyrie]
+trait GeneralizedSuccessorInstances {
+  implicit def eyrieNonSuccessorBasedInstance[A, L, R](
+    implicit
+    A: Subdivision[A, L, R],
+    L: NonSuccessor[L],
+    R: NonSuccessor[R]
+  ): NonSuccessor[A] =
+    new NonSuccessor[A] { }
+}
+
 private[eyrie]
 trait SuccessorInstances {
-  implicit def eyrieDiSuccessorBasedInstance[A, B, C, L, R](
+  implicit def eyrieDiSuccessorBasedInstance[A, L, R, B, C](
     implicit
     A: DiSuccessor[A, L, R, C],
     L: Convertible[L, B],
@@ -76,7 +87,7 @@ trait PotentialSuccessorInstances {
         A.subdivide(_).toOption.map(R.lastSegment)
     }
 
-  implicit def eyrieDiPotentialSuccessorBasedInstance[A, C, L, R](
+  implicit def eyrieDiPotentialSuccessorBasedInstance[A, L, R, C](
     implicit
     A: DiPotentialSuccessor[A, L, R, C],
     L: Convertible[L, A],

core/src/main/scala/eyrie/ops/Descendant.scala

@@ -3,7 +3,7 @@ package eyrie.ops
 import eyrie.instances.{DescendantByInputInstances, DescendantInstances}
 import simulacrum.typeclass
 
-trait Descendant[A, B] {
+trait Descendant[A, B] extends GeneralizedDescendant[A, B] {
   def root: A => B
 }
 

core/src/main/scala/eyrie/ops/GeneralizedDescendant.scala

@@ -0,0 +1,7 @@
+package eyrie.ops
+
+import eyrie.instances.GeneralizedDescendantInstances
+
+trait GeneralizedDescendant[A, B]
+
+object GeneralizedDescendant extends GeneralizedDescendantInstances

core/src/main/scala/eyrie/ops/GeneralizedSuccessor.scala

@@ -0,0 +1,7 @@
+package eyrie.ops
+
+import eyrie.instances.GeneralizedSuccessorInstances
+
+trait GeneralizedSuccessor[A, B, C]
+
+object GeneralizedSuccessor extends GeneralizedSuccessorInstances

core/src/main/scala/eyrie/ops/Successor.scala

@@ -3,7 +3,7 @@ package eyrie.ops
 import eyrie.instances.{SuccessorByInputInstances, SuccessorInstances}
 import simulacrum.typeclass
 
-trait Successor[A, B, C] {
+trait Successor[A, B, C] extends GeneralizedSuccessor[A, B, C] {
   def parent: A => B
   def lastSegment: A => C
 }

core/src/main/scala/eyrie/ops/package.scala

@@ -1,8 +1,8 @@
 package eyrie
 
 package object ops {
-  type NonSuccessor[A] = Successor[A, Nothing, Nothing]
+  type NonSuccessor[A] = GeneralizedSuccessor[A, Nothing, Nothing]
 
   type TrivialDescendant[A] = Descendant[A, A]
-  type NonDescendant[A] = Descendant[A, Nothing]
+  type NonDescendant[A] = GeneralizedDescendant[A, Nothing]
 }

file/src/main/scala/eyrie/file/instances/FilePathSuccessor.scala → file/src/main/scala/eyrie/file/instances/FilePathDescendant.scala

@@ -32,10 +32,6 @@ object RelativeFilePathDescendant extends NonDescendant[RelativeFile[Any]]
   with Successor[RelativeFile[Any], FilePath.Relative[Any], FileName[Any]] {
   import eyrie.file.syntax.asJava._
 
-  override
-  def root: RelativeFile[Any] => Nothing =
-    _ => throw new UnsupportedOperationException("Unexpected invocation")
-
   private
   def relative[S](path: Path): FilePath.Relative[S] =
     if (path.getNameCount < 2 && Option(path.getFileName).forall(_.toString.isEmpty)) {
@@ -81,32 +77,12 @@ object AbsoluteFilePathDescendant extends Descendant[AbsoluteFile[Any], RootDire
 
 private
 object FilePathNonDescendant extends NonDescendant[IdentityFilePath[Any]]
-  with NonSuccessor[IdentityFilePath[Any]] {
-  override
-  def root: IdentityFilePath[Any] => Nothing =
-    _ => throw new UnsupportedOperationException("Unexpected invocation")
-
-  override
-  def parent: IdentityFilePath[Any] => Nothing =
-    _ => throw new UnsupportedOperationException("Unexpected invocation")
-
-  override
-  def lastSegment: IdentityFilePath[Any] => Nothing =
-    _ => throw new UnsupportedOperationException("Unexpected invocation")
-}
+  with NonSuccessor[IdentityFilePath[Any]]
 
 private
 object FilePathTrivialDescendant extends TrivialDescendant[RootDirectory[Any]]
   with NonSuccessor[RootDirectory[Any]] {
   override
   def root: RootDirectory[Any] => RootDirectory[Any] =
     identity
-
-  override
-  def parent: RootDirectory[Any] => Nothing =
-    _ => throw new UnsupportedOperationException("Unexpected invocation")
-
-  override
-  def lastSegment: RootDirectory[Any] => Nothing =
-    _ => throw new UnsupportedOperationException("Unexpected invocation")
 }