REDNBLACK · June 14, 2019 08:41 · Jun 14, 2019 · Jun 14, 2019
diff --git a/Monocle.scala b/Monocle.scala
@@ -1,4 +1,4 @@
-package ru.tinkoff
+package pkg
 
 import cats.{Applicative, Traverse}
 

diff --git a/Monocle.scala b/Monocle.scala
@@ -0,0 +1,62 @@
+package ru.tinkoff
+
+import cats.{Applicative, Traverse}
+
+import monocle.macros.{GenLens, Lenses}
+import monocle.macros.syntax.lens._
+import monocle.function.all._
+import cats.syntax.option._
+
+import monocle.Traversal
+import monocle.function.FilterIndex.fromTraverse
+import monocle.function.{FilterIndex, FilterIndexFunctions}
+
+object Demo extends App {
+  @Lenses
+  case class Company(name: String, employees: List[Employee])
+
+  @Lenses
+  case class Employee(name: String, data: List[Field])
+
+  @Lenses
+  case class Field(name: String, value: Option[String])
+
+  val company1 = Company("awesome inc", List(
+    Employee("Steven", Field("age", "20".some) :: Nil),
+    Employee("Carl", Field("age", "30".some) :: Nil),
+    Employee("Max", Field("married", "true".some) :: Nil)
+  ))
+
+
+  object Impl {
+    abstract class Filter[S, A] extends Serializable {
+      def filter(predicate: A => Boolean): Traversal[S, A]
+    }
+
+    trait FilterFunctions {
+      def filter[S, A](predicate: A => Boolean)(implicit ev: Filter[S, A]): Traversal[S, A] = ev.filter(predicate)
+
+      def filterNot[S, A](predicate: A => Boolean)(implicit ev: Filter[S, A]): Traversal[S, A] = ev.filter(!predicate(_))
+    }
+
+    object Filter extends FilterFunctions {
+      import cats.syntax.traverse._
+      import cats.syntax.applicative._
+
+      implicit def traverseFilter[S[_]: Traverse, A]: Filter[S[A], A] = predicate => new Traversal[S[A], A] {
+        def modifyF[F[_]: Applicative](f: A => F[A])(s: S[A]): F[S[A]] =
+          s.traverse(a => if (predicate(a)) f(a) else a.pure[F])
+      }
+    }
+  }
+
+  import Impl.Filter._
+  import cats.instances.list._
+
+  val lens = GenLens[Company](_.employees) ^|->> each ^|-> GenLens[Employee](_.data) ^|->> filter((_: Field).name == "age") modify(
+    _.copy(value = "100500".some)
+  )
+
+  println(company1)
+  println(lens(company1))
+}