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August 16, 2016 09:08
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scalaExercisesCats.scala
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| import cats._, cats.implicits._ | |
| import cats.data.Xor | |
| object Main extends App { | |
| assert(Foldable[List].foldK(List(List(1, 2), List(3, 4, 5))) == List(1,2,3,4,5)) | |
| assert(Foldable[List].foldK(List(None, Option("two"), Option("three"))) == Some("two")) | |
| def parseInt(s: String): Option[Int] = | |
| Xor.catchOnly[NumberFormatException](s.toInt).toOption | |
| assert(Foldable[List].traverse_(List("1", "2", "3"))(parseInt) == Some(())) | |
| assert(Foldable[List].traverse_(List("a", "b", "c"))(parseInt) == None) | |
| val FoldableListOption = Foldable[List].compose[Option] | |
| assert(FoldableListOption.fold(List(Option(1), Option(2), Option(3), Option(4))) == 10) | |
| assert(FoldableListOption.fold(List(Option("1"), Option("2"), None, Option("3"))) == "123") | |
| // MonoidK | |
| // Traverse | |
| // cats.data.Reader // Reader[E, A] == Kleisli[Id, E, A] | |
| import cats.Semigroup | |
| import cats.data.{NonEmptyList, OneAnd, Validated, ValidatedNel, Xor} | |
| import cats.std.list._ | |
| import cats.syntax.traverse._ | |
| def parseIntXor(s: String): Xor[NumberFormatException, Int] = | |
| Xor.catchOnly[NumberFormatException](s.toInt) | |
| def parseIntValidated(s: String): ValidatedNel[NumberFormatException, Int] = | |
| Validated.catchOnly[NumberFormatException](s.toInt).toValidatedNel | |
| assert(List("1", "2", "3").traverseU(parseIntXor) == Xor.Right(List(1, 2, 3))) | |
| assert(List("1", "abc", "3").traverseU(parseIntXor).isLeft) | |
| import cats.data.{NonEmptyList, OneAnd, ValidatedNel} | |
| assert(List("1", "2", "3").traverseU(parseIntValidated).isValid) | |
| import cats.syntax.foldable._ | |
| assert(List(Option(1), Option(2), Option(3)).sequence_ == Some(())) | |
| assert(List(Option(1), None, Option(3)).sequence_ == None) | |
| // IDENTITY | |
| val one: Int = 1 | |
| Functor[Id].map(one)(_ + 1) | |
| assert(Applicative[Id].pure(42) == 42) | |
| Monad[Id].map(one)(_ + 1) | |
| Monad[Id].flatMap(one)(_ + 1) | |
| val fortytwo: Int = 42 | |
| assert(Comonad[Id].coflatMap(fortytwo)(_ + 1) == 43) | |
| // Xor | |
| val right: String Xor Int = Xor.Right(41) | |
| assert(right.map(_ + 1) == Xor.Right(42)) | |
| val left: String Xor Int = Xor.Left("went of") | |
| } |
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