Modad.re

module type Monad = {
  type m(_);
  let flatMap: m('a) => ('a => m('b)) => m('b);
};


module ListMonad: Monad {
  type t('a) = list('a)
  let rec flatMap = (ma, f) => switch (ma) {
  | [] => []
  | [x, ...xs] => List.concat([f(x), flatMap(xs, f)])
  }
}


open ListMonad;

Js.log([1,2,3])
Js.log(
	[1,2,3]->flatMap(x => [x, x])
)