Polymorphism in Nim

[xigoi]

This seems to work, but for some reason it shows a wrong value for `y`.
    
    
    method `$`(x: Uno): string {.base.} =
      system.`$`(x)
    
    method `$`(x: Due): string =
      system.`$`(x)
    
    method `$`(x: Tre): string =
      system.`$`(x)
    
    
    Run