require("@babel/polyfill")
const { implement, Functor } = require("@masaeedu/fp")

const Fluture= require("fluture")

// We can just get map from of and chain for free everywhere
const deriveFunctor = implement(Functor)

// Identity monad
const id = x => x;
const Identity = deriveFunctor({ of: id, chain: id });

const Maybe = (() => {
  // ADT
  const Just = x => ({ hasValue: true, x });
  const Nothing = { hasValue: false };
  const match = ({ Just, Nothing }) => ({ hasValue, x }) =>
    hasValue ? Just(x) : Nothing;

  // Monad transformer
  const T = M => {
    // Monad
    const of = x => M.of(Just(x));
    const chain = f =>
      M.chain(match({
        Nothing: M.of(Nothing),
        Just: f
      }));

    // MonadTrans
    const liftT = M.map(Just);

    return deriveFunctor({ of, chain, liftT })
  };

  // Monad
  const { of, chain } = T(Identity)

  return deriveFunctor({ Just, Nothing, match, T, of, chain });
})();

const MaybeOfFluture = Maybe.T(Fluture)
const tests = [
  MaybeOfFluture.map(x => x * 2)(Fluture.of(Maybe.Nothing)), // => Nothing
  MaybeOfFluture.map(x => x * 2)(Fluture.of(Maybe.Just(21))) // => 42
]

tests.map(f => f.fork(console.error, console.log))