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  1. object Fuels {
  2.  
  3.   trait Monoid[F] {
  4.     def zero: F
  5.     def append(f1: F, f2: F): F
  6.   }
  7.  
  8.   object Monoid {
  9.     def fold[F](as: Seq[F])(implicit m: Monoid[F]): F = as.foldLeft(m.zero)(m.append)
  10.   }
  11.  
  12.   case class Fuel[F <: FuelType](amount: Double, fuelType: F = Petrol) {
  13.     def +(that : Fuel[F]): Fuel[F] = {
  14.       copy(amount = this.amount + that.amount)
  15.     }
  16.   }
  17.  
  18.   def add[F <: FuelType](x: Fuel[F], y: Fuel[F]): Fuel[F] = x + y
  19.  
  20.   sealed trait FuelType {
  21.     val name : String
  22.   }
  23.   case object Petrol extends FuelType{
  24.     override val name = "Petrol"
  25.   }
  26.   case object Diesel extends FuelType{
  27.     override val name = "Diesel"
  28.   }
  29.   case object Hydrogen extends FuelType{
  30.     override val name = "Hydrogen"
  31.   }
  32.  
  33.   implicit def fuelMonoid[F <:FuelType](implicit fuelType: F): Monoid[Fuel[F]] = new Monoid[Fuel[F]] {
  34.     override def zero: Fuel[F] = Fuel(0, fuelType)
  35.     override def append(m1: Fuel[F], m2: Fuel[F]): Fuel[F] = m1 + m2
  36.   }
  37. }
  38.  
  39. object Main {
  40.   def main (args: Array[String] ) {
  41.     import Fuels._
  42.     println(Fuel(10, Petrol) + Fuel(20, Petrol))
  43.     println(add(Fuel(10, Petrol), Fuel(20, Petrol)))
  44.     implicit val petrolM = fuelMonoid(Petrol)
  45.     println(Monoid.fold(Seq(Fuel(10, Petrol), Fuel(20, Petrol), Fuel(30, Petrol))))
  46.   }
  47. }
Success #stdin #stdout 0.39s 382080KB
comments (?)
stdin 
Standard input is empty
stdout 
Fuel(30.0,Petrol)
Fuel(30.0,Petrol)
Fuel(60.0,Petrol)
https://ideone.com/QKuCad
language:
Scala (scala 2.12.8)
created:
10 years ago
visibility:
public

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