Arrow.re

module Action = {
  type t('i, 'o) = 'i => 'o;

  let chain = (action1, action2, arg) => arg |> action1 |> action2;
};

module Rule = {
  type t('i, 'o) = {
    action: Action.t('i, 'o),
    f: option(unit),
  };

  let make = action => {action, f: None};
  let chain = ({action: a1, _}, {action: a2, _}) => {
    action: Action.chain(a1, a2),
    f: None,
  };

  let execute = (input, {action, _}) => action(input);
};

let test = () => {
  let hello = Rule.make(() => "Hello");
  let plusWorld = Rule.make(s => s ++ ", world");
  let print = Rule.make(print_endline);
  let all = Rule.(chain(chain(hello, plusWorld), print));
  Rule.execute((), all);
};