Scala example source code file (t3399.scala)

This example Scala source code file (t3399.scala) is included in the DevDaily.com "Java Source Code Warehouse" project. The intent of this project is to help you "Learn Java by Example" ^TM.

Java - Scala tags/keywords

acc, add, apply, f, f, fold, fold, foldr, nat, nat, succ, type, type, value

The Scala t3399.scala source code

object Nats {
    sealed trait Nat {
        // fold right on N, N-1, ..., 1
        type FoldR[Init <: Type, Type, F <: Fold[Nat, Type]] <: Type
    }
    sealed trait _0 extends Nat {
        type FoldR[Init <: Type, Type, F <: Fold[Nat, Type]] = Init
    }
    sealed trait Succ[N <: Nat] extends Nat {
        type FoldR[Init <: Type, Type, F <: Fold[Nat, Type]] =
          F#Apply[Succ[N], N#FoldR[Init, Type, F]]
    }
    
    type Add[A <: Nat, B <: Nat] = A#FoldR[B, Nat, Inc]
    trait Fold[-Elem, Value] {
        type Apply[N <: Elem, Acc <: Value] <: Value
    }
    type Inc = Fold[Any, Nat] {
        type Apply[N <: Any, Acc <: Nat] = Succ[Acc]
    }
    
    type _1 = Succ[_0]
    implicitly[ Add[_1, _1] =:= _1]
}