pyr by example

Polymorphism

Pyr uses enums with payloads and pattern matching for polymorphic dispatch. Define variants, match on them, and use UFCS for method-style calls.

enums model a closed set of types. each variant can carry its own data.

 
enum Animal {
  Dog(str)
  Cat(str)
  Fish(str, int)
}

a single function handles all variants via match. the compiler enforces exhaustiveness - add a variant and every match must handle it.

 
fn speak(a: Animal) -> str {
  match a {
    Dog(name) -> "{name} says woof"
    Cat(name) -> "{name} says meow"
    Fish(name, bubbles) -> "{name} blows {bubbles} bubbles"
  }
}

fn name(a: Animal) -> str {
  match a {
    Dog(n) -> n
    Cat(n) -> n
    Fish(n, _) -> n
  }
}

fn main() {
  // UFCS: pet.speak() calls speak(pet)
  pet = Dog("Rex")
  println(pet.speak())
  println(pet.name())

  // works with collections
  pets = [Dog("Rex"), Cat("Whiskers"), Fish("Nemo", 3)]
  for p in pets {
    println(p.speak())
  }
}
 
$ pyr run polymorphism.pyr
Rex says woof
Rex
Rex says woof
Whiskers says meow
Nemo blows 3 bubbles