endpoints4s.algebra

An algebra interface for describing algebraic data types. Such descriptions can be interpreted to produce a JSON schema of the data type, a JSON encoder, a JSON decoder, etc.

A description contains the fields of a case class and their type, and the constructor names of a sealed trait.

For instance, consider the following record type:

 case class User(name: String, age: Int)

Its description is the following:

 object User {
   implicit val schema: JsonSchema[User] = (
     field[String]("name") zip
     field[Int]("age")
   ).xmap((User.apply _).tupled)(Function.unlift(User.unapply))
 }

The description says that the record type has two fields, the first one has type String and is named “name”, and the second one has type Int and name “age”.

To describe sum types you have to explicitly “tag” each alternative:

 sealed trait Shape
 case class Circle(radius: Double) extends Shape
 case class Rectangle(width: Double, height: Double) extends Shape

 object Shape {
   implicit val schema: JsonSchema[Shape] = {
     val circleSchema = field[Double]("radius").xmap(Circle)(Function.unlift(Circle.unapply))
     val rectangleSchema = (
       field[Double]("width") zip
       field[Double]("height")
     ).xmap((Rectangle.apply _).tupled)(Function.unlift(Rectangle.unapply))
     (circleSchema.tagged("Circle") orElse rectangleSchema.tagged("Rectangle"))
       .xmap[Shape] {
         case Left(circle) => circle
         case Right(rect)  => rect
       } {
         case c: Circle    => Left(c)
         case r: Rectangle => Right(r)
       }
   }
 }

Helper trait that can be mixed into JsonSchemas to implement (as no-ops) the documentation related methods. This is useful for implementing any non-documentation inteprereters.

Generated trait that provides JsonSchema constructors for tuples from 2 to 22 elements.

endpoints4s.algebra

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