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TimWSpenceTimWSpence
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Derive ShowPretty (typelevel#490)
* WIP derive ShowPretty * Derive ShowPretty * Derive ShowPretty WIP * Fix show pretty derivations
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‎core/src/main/scala-3/cats/derived/DerivedShowPretty.scala

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package cats.derived
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import cats.Show
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import shapeless3.deriving.{Continue, K0, Labelling}
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import scala.annotation.implicitNotFound
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import scala.compiletime.*
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import scala.deriving.Mirror
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trait ShowPretty[A] extends Show[A]:
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def showLines(a: A): List[String]
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def show(a: A): String = showLines(a).mkString(System.lineSeparator)
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object ShowPretty:
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inline def apply[A](using A: ShowPretty[A]): A.type = A
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@implicitNotFound("""Could not derive an instance of ShowPretty[A] where A = ${A}.
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Make sure that A satisfies one of the following conditions:
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* it is a case class where all fields have a Show instance
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* it is a sealed trait where all subclasses have a Show instance""")
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type DerivedShowPretty[A] = Derived[ShowPretty[A]]
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object DerivedShowPretty:
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opaque type Or[A] = A => List[String]
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object Or extends OrInstances:
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def apply[A](instance: A => List[String]): Or[A] = instance
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extension [A](or: Or[A]) def apply(a: A): List[String] = or(a)
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sealed abstract class OrInstances:
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inline given [A]: Or[A] = summonFrom {
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case instance: Show[A] => Or((a: A) => instance.show(a).split(System.lineSeparator).toList)
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case derived: DerivedShowPretty[A] => Or(derived.instance.showLines(_))
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}
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inline def apply[A]: ShowPretty[A] =
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import DerivedShowPretty.given
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summonInline[DerivedShowPretty[A]].instance
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given [A](using inst: K0.ProductInstances[Or, A], labelling: Labelling[A]): DerivedShowPretty[A] =
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new Product[A] {}
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given [A](using inst: => K0.CoproductInstances[Or, A]): DerivedShowPretty[A] =
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new Coproduct[A] {}
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trait Product[A](using inst: K0.ProductInstances[Or, A], labelling: Labelling[A]) extends ShowPretty[A]:
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def showLines(a: A): List[String] =
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val prefix = labelling.label
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val labels = labelling.elemLabels
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val n = labels.size
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if n <= 0 then List(s"$prefix()")
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else
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var lines: List[String] = List(")")
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val inner = inst.project(a)(n - 1)([t] => (show: Or[t], x: t) => show.apply(x))
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inner match
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case Nil => lines = s" ${labels(n - 1)} = \"\"," :: lines
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case h :: t => lines = s" ${labels(n - 1)} = $h" :: t.map(s => " " + s) ::: lines
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var i = n - 2
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while i >= 0 do
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val inner = inst.project(a)(i)([t] => (show: Or[t], x: t) => show.apply(x))
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inner match
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case Nil => lines = s" ${labels(i)} = \"\"," :: lines
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case v :: Nil => lines = s" ${labels(i)} = $v," :: lines
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case h :: t => lines = s" ${labels(i)} = $h" :: t.init.map(s => " " + s) ::: s" ${t.last}," :: lines
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i -= 1
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lines = s"$prefix(" :: lines
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lines
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trait Coproduct[A](using inst: K0.CoproductInstances[Or, A]) extends ShowPretty[A]:
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def showLines(a: A): List[String] =
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inst.fold(a)([t] => (st: Or[t], t: t) => st.apply(t))

‎core/src/main/scala-3/cats/derived/package.scala

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@@ -29,6 +29,7 @@ extension (x: MonoidK.type) inline def derived[F[_]]: MonoidK[F] = DerivedMonoid
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extension (x: Contravariant.type) inline def derived[F[_]]: Contravariant[F] = DerivedContravariant[F]
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extension (x: Invariant.type) inline def derived[F[_]]: Invariant[F] = DerivedInvariant[F]
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extension (x: PartialOrder.type) inline def derived[A]: PartialOrder[A] = DerivedPartialOrder[A]
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extension (x: ShowPretty.type) inline def derived[A]: ShowPretty[A] = DerivedShowPretty[A]
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object semiauto:
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inline def eq[A]: Eq[A] = DerivedEq[A]
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inline def contravariant[F[_]]: Contravariant[F] = DerivedContravariant[F]
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inline def invariant[F[_]]: Invariant[F] = DerivedInvariant[F]
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inline def partialOrder[A]: PartialOrder[A] = DerivedPartialOrder[A]
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inline def showPretty[A]: ShowPretty[A] = DerivedShowPretty[A]
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object auto:
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object eq:
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object partialOrder:
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inline given [A](using NotGiven[PartialOrder[A]]): PartialOrder[A] = DerivedPartialOrder[A]
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object showPretty:
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inline given [A](using NotGiven[Show[A]]): ShowPretty[A] = DerivedShowPretty[A]

‎core/src/test/scala-3/cats/derived/ShowPrettySuite.scala

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package cats
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package derived
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import cats.laws.discipline.SerializableTests
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import scala.compiletime.*
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class ShowPrettySuite extends KittensSuite:
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import ShowPrettySuite.*
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import ShowPrettySuite.given
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import TestDefns.*
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inline def showPretty[A](value: A): String =
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summonInline[ShowPretty[A]].show(value)
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inline def testShowPretty(context: String): Unit = {
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checkAll(s"$context.ShowPretty is Serializable", SerializableTests.serializable(summonInline[ShowPretty[IntTree]]))
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test(s"$context.ShowPretty[Foo]") {
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val value = Foo(42, Option("Hello"))
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val pretty = """
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|Foo(
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| i = 42,
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| b = Some(Hello)
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|)
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""".stripMargin.trim
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assertEquals(showPretty(value), pretty)
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}
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test(s"$context.ShowPretty[Outer]") {
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val value = Outer(Inner(3))
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val pretty = """
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|Outer(
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| in = Inner(
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| i = 3
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| )
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|)
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""".stripMargin.trim
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assertEquals(showPretty(value), pretty)
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}
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test(s"$context.ShowPretty[IntTree]") {
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val value: IntTree = IntNode(IntLeaf(1), IntNode(IntNode(IntLeaf(2), IntLeaf(3)), IntLeaf(4)))
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val pretty = """
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|IntNode(
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| l = IntLeaf(
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| t = 1
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| ),
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| r = IntNode(
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| l = IntNode(
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| l = IntLeaf(
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| t = 2
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| ),
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| r = IntLeaf(
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| t = 3
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| )
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| ),
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| r = IntLeaf(
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| t = 4
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| )
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| )
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|)
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""".stripMargin.trim
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assertEquals(showPretty(value), pretty)
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}
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test(s"$context.ShowPretty[GenericAdt[Int]]") {
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val value: GenericAdt[Int] = GenericAdtCase(Some(1))
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val pretty = """
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|GenericAdtCase(
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| value = Some(1)
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|)
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""".stripMargin.trim
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assertEquals(showPretty(value), pretty)
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}
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test(s"$context.ShowPretty[People]") {
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val value = People("Kai", ContactInfo("303-123-4567", Address("123 1st St", "New York", "NY")))
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val pretty = """
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|People(
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| name = Kai,
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| contactInfo = ContactInfo(
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| phoneNumber = 303-123-4567,
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| address = 123 1st St New York NY
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| )
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|)
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""".stripMargin.trim
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assertEquals(showPretty(value), pretty)
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}
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test(s"$context.ShowPretty[ListField]") {
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val value = ListField("a", List(ListFieldChild(1)))
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val pretty = """
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|ListField(
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| a = a,
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| b = List(ListFieldChild(
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| c = 1
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| ))
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|)
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""".stripMargin.trim
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assertEquals(showPretty(value), pretty)
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}
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test(s"$context.ShowPretty[Interleaved[Int]]") {
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val value = Interleaved(1, 2, 3, Vector(4, 5, 6), "789")
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val pretty = """
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|Interleaved(
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| i = 1,
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| t = 2,
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| l = 3,
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| tt = Vector(4, 5, 6),
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| s = 789
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|)
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""".stripMargin.trim
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assertEquals(showPretty(value), pretty)
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}
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test(s"$context.ShowPretty[Tree[Int]]") {
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val value: Tree[Int] = Node(Leaf(1), Node(Node(Leaf(2), Leaf(3)), Leaf(4)))
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val pretty = """
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|Node(
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| left = Leaf(
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| value = 1
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| ),
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| right = Node(
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| left = Node(
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| left = Leaf(
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| value = 2
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| ),
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| right = Leaf(
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| value = 3
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| )
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| ),
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| right = Leaf(
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| value = 4
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| )
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| )
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|)
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""".stripMargin.trim
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assertEquals(showPretty(value), pretty)
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}
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test(s"$context.ShowPretty respects existing instances") {
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val value = Box(Bogus(42))
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val pretty = """
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|Box(
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| content = Blah
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|)
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""".stripMargin.trim
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assertEquals(showPretty(value), pretty)
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}
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}
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locally {
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import auto.showPretty.given
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testShowPretty("auto")
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}
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locally {
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import semiInstances.given
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testShowPretty("semiauto")
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}
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object ShowPrettySuite:
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import TestDefns.*
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given Show[Address] = Show.show { a =>
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List(a.street, a.city, a.state).mkString(" ")
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}
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final case class Bogus(value: Int)
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object Bogus:
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given Show[Bogus] = Show.show(_ => "Blah")
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object semiInstances:
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given ShowPretty[Foo] = semiauto.showPretty
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given ShowPretty[Outer] = semiauto.showPretty
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given ShowPretty[IntTree] = semiauto.showPretty
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given ShowPretty[GenericAdt[Int]] = semiauto.showPretty
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given ShowPretty[People] = semiauto.showPretty
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given ShowPretty[ListFieldChild] = semiauto.showPretty
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given ShowPretty[ListField] = semiauto.showPretty
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given ShowPretty[Interleaved[Int]] = semiauto.showPretty
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given ShowPretty[Tree[Int]] = semiauto.showPretty
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given ShowPretty[Box[Bogus]] = semiauto.showPretty

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