Concepts already implemented in Nim at time of publishing

[ZoomRmc]

VerdagonSite/src/blog/0.2/concept-functions.vmd

Line 53 in da63cb0

The only existing language today which can accomplish something like this is C++, with its `requires requires` clause:

Not sure when exactly, but they had been implemented for a few years by 2022 when the article was published.
The current state: https://nim-lang.org/docs/manual_experimental.html#concepts
The redesign (testing implementation exists): nim-lang/RFCs#168

type
  Strong = concept t
    t.strength is int

  Damaging = concept a, b
    calcDamage(a, b) is int

func calcDamage(attacker, target: Strong): int =
  attacker.strength - target.strength

func battle(attacker, defender: Damaging): int =
  calcDamage(attacker, defender)

type Ship = object
  strength: int

let rocinante = Ship(strength: 10)
let  bessie = Ship(strength: 9000)

echo bessie.battle(rocinante)

[Verdagon]

Added a mention for Nim's concepts, thanks for the heads up!