Reason Phantom Type Animal module type

ReasonAnimalType.re

module type Animal = {
  /* Define abstract types t, dog, and cat */
  type t('a);
  type dog;
  type cat;
  
  /* helpers to create a type dog or cat */
  let makeDog: string => t(dog);
  let makeCat: string => t(cat);
  let mate: (t('a), t('a)) => string;
};