Prisms

object Prisms {
    
    // Sum type constructors

    def left[B, C](x: B): (B=>C)=>C = {
        (k) => {
            k(x)
        }
    }
    
    def right[B, C](y: C): (B=>C)=>C = {
        (k)=> y
    }
    
    // Simulation of call-cc
    
    case class Thrown[A](x: A) extends Throwable
    
    def callCC[P, Q](f: (P=>Q)=>P): P = {
        try {
            def h(x: P): Q = {
                throw Thrown(x)
            }
            f(h)
        } catch {
            case Thrown(x) => {
                x.asInstanceOf[P]
            }
        }
    }
    
    // Sum type destructor
    
    def either[B, C, X](x: (B=>C)=>C, f: B=>X, g: C=>X): X = {
        callCC((raise: X=>C)=> {
            def h(y: B): C = {
                raise(f(y))
            }
            g(x(h))          
        })
    }
    
    def main(argv: Array[String]) = {
        val x = left(1)
        val y = right(true)
        either(x, (i:Int)=>println("left: "+(i*3)), (j:Boolean)=>println("right: "+(!j))) // prints left: 3
        either(y, (i:Int)=>println("left: "+(i*3)), (j:Boolean)=>println("right: "+(!j))) // prints right: false
    }
        
}