sir-wabbit · November 1, 2018 04:25 · Nov 1, 2018
diff --git a/shapely-POC.scala b/shapely-POC.scala
@@ -0,0 +1,84 @@
+trait Iso[A, B] {
+  def to(a: A): B
+  def from(b: B): A
+}
+
+trait Derivable[F[_]] {
+  type Fields[_]
+  def fieldOf[A](name: String, value: F[A]): Fields[A]
+  def fieldUnit: Fields[Unit]
+  def fieldZip[A, B](left: Fields[A], right: Fields[B]): Fields[(A, B)]
+  def fieldMap[A, B](fa: Fields[A])(f: Iso[A, B]): Fields[B]
+
+  type Cases[_]
+  def caseOf[A](name: String, fields: Fields[A]): Cases[A]
+  def caseUnit: Cases[Nothing]
+  def caseZip[A, B](left: Cases[A], right: Cases[B]): Cases[Either[A, B]]
+  def caseMap[A, B](fa: Cases[A])(f: Iso[A, B]): Cases[B]
+
+  def coproduct[A](name: String, cases: Cases[A]): F[A]
+  def product[A](name: String, fields: Fields[A]): F[A]
+}
+
+trait Show[A] {
+  def show(a: A): String
+}
+
+val showDerivable: Derivable[Show] = new Derivable[Show] { 
+  type Fields[A] = A => List[String]
+
+  def fieldOf[A](name: String, value: Show[A]): Fields[A] =
+    a => List(name + "=" + value.show(a))
+
+  def fieldUnit: Fields[Unit] =
+    a => Nil
+
+  def fieldZip[A, B](left: Fields[A], right: Fields[B]): Fields[(A, B)] =
+    { case (a, b) => left(a) ++ right(b) }
+
+  def fieldMap[A, B](fa: Fields[A])(f: Iso[A, B]): Fields[B] =
+    b => fa(f.from(b))
+
+  type Cases[A] = A => String
+
+  def caseOf[A](name: String, fields: Fields[A]): Cases[A] =
+    a => name + "(" + fields(a).mkString(", ") + ")"
+
+  def caseUnit: Cases[Nothing] =
+    a => a
+
+  def caseZip[A, B](left: Cases[A], right: Cases[B]): Cases[Either[A, B]] =
+    ab => ab.fold(left, right)
+
+  def caseMap[A, B](fa: Cases[A])(f: Iso[A, B]): Cases[B] =
+    b => fa(f.from(b))
+
+  def coproduct[A](name: String, cases: Cases[A]): Show[A] =
+    a => cases(a)
+
+  def product[A](name: String, fields: Fields[A]): Show[A] =
+    a => name + "(" + fields(a).mkString(", ") + ")"
+}
+
+implicit val intShow: Show[Int] = a => a.toString
+implicit val boolShow: Show[Boolean] = a => a.toString
+
+final case class Foo(i: Int, b: Boolean)
+
+val fooShow = {
+  import showDerivable._
+
+  val fooIso = new Iso[(Int, Boolean), Foo] {
+    def to(p: (Int, Boolean)): Foo = Foo(p._1, p._2)
+    def from(p: Foo): (Int, Boolean) = (p.i, p.b)
+  }
+
+  product("Foo", fieldMap(fieldZip(
+    fieldOf("i", implicitly[Show[Int]]),
+    fieldOf("b", implicitly[Show[Boolean]])))(fooIso))
+}
+
+println(fooShow.show(Foo(1, true)))
+
+
+///