typeclass #Copy =
  & copy : #Copy -> #Copy

typeclass (#Ord : #Eq) =
  & ( < ) : #Ord -> #Ord -> Bool
  & ( > ) : #Ord -> #Ord -> Bool
  & ( <= ) : #Ord -> #Ord -> Bool
  & ( >= ) : #Ord -> #Ord -> Bool

typeclass (#D : #A #B #C) 'A 'B =
  & do_something : Unit -> (& 'A & 'B)

typeclass #E 'A =
  & do_something : Unit -> 'A

namespace const ord : #Ord {
  def ( <= ) : a b = (a < b) || (a == b)
  def ( > ) : a b = !(a <= b)
  def ( >= ) : a b = !(a < b)
}

// === ?? dependent types ?? ===
//
// typeclass #F : (a : Int) (b : Int) =
//   & do_something Int -> Int
//
// namespace (f : #F a b c) {
//   require do_sometihng a = b
// }
//
// ===

// ?? operators over functions (without arguments, like "def <= = < || ==;") ??
// ?? define operators like OCaml ??
// ?? denote moved type ??
// ?? "trait" VS "typeclass" ??