selector-fp-ts.ts

import { Monad2 } from "fp-ts/lib/Monad";
import { HKT } from "fp-ts/lib/HKT";
import { createSelector, Selector } from "reselect";
import { sequenceT } from "fp-ts/lib/Apply";
import { Do } from "fp-ts-contrib/lib/Do";

declare module "fp-ts/lib/HKT" {
  interface URI2HKT2<L, A> {
    Selector: Selector<L, A>;
  }
}

export type Foo = HKT<any, any>

export const URI = "Selector";
export type URI = typeof URI;

export const selector: Monad2<URI> = {
  URI,
  of<State, A>(a: A): Selector<State, A> {
    return () => a;
  },
  map<State, A, B>(fa: Selector<State, A>, f: (a: A) => B): Selector<State, B> {
    return createSelector(
      fa,
      f
    );
  },
  ap<State, A, B>(fab: Selector<State, (a: A) => B>, fa: Selector<State, A>): Selector<State, B> {
    return createSelector(
      fab,
      fa,
      (ab, a) => ab(a)
    );
  },
  chain<State, A, B>(fa: Selector<State, A>, f: (a: A) => Selector<State, B>): Selector<State, B> {
    return createSelector(
      (state: State) => {
        const a = fa(state);
        const fb = f(a);
        return fb(state);
      },
      fb => fb
    );
  }
};

sequenceT(selector) // passes

Do(selector) //fails with:
// selector-fp-ts.ts:50:4 - error TS2345: Argument of type 'Monad2<"Selector">' is not assignable to parameter of type 'Monad<"Selector">'.
//   Types of property 'of' are incompatible.
//     Type '<L, A>(a: A) => Selector<L, A>' is not assignable to type '<A>(a: A) => HKT<"Selector", A>'.
//       Type 'Selector<{}, A>' is missing the following properties from type 'HKT<"Selector", A>': _URI, _A