Higher Kinded Data fp-ts

HKD.ts

import {Applicative1} from 'fp-ts/lib/Applicative';
import * as Array from 'fp-ts/lib/Array';
import {Kind, URIS} from 'fp-ts/lib/HKT';
import {pipe} from 'fp-ts/lib/pipeable';

export type HKD<F extends URIS, A> = {[K in keyof A]: Kind<F, A[K]>};

export const sequenceHKD = <F extends URIS>(F: Applicative1<F>) => <A>(
  lifted: HKD<F, A>,
): Kind<F, A> => {
  const fa = pipe(
    lifted,
    Object.keys,
    Array.map(key => {
      const fak = lifted[key] as Kind<F, unknown>;
      const foo = F.map(fak, value => (obj: Partial<A>) => ({
        ...obj,
        [key]: value,
      }));
      return foo;
    }),
    Array.reduce(F.of({}), (acc, fab) => F.ap(fab, acc)),
  ) as Kind<F, A>;

  return fa;
};

export const liftHKD = <F extends URIS>(F: Applicative1<F>) => <A>(
  obj: A,
): HKD<F, A> => {
  const lifted = pipe(
    obj,
    Object.keys,
    Array.map(key => {
      const liftedValue = F.of(obj[key] as unknown);
      return (acc: Partial<HKD<F, A>>) => ({
        ...acc,
        [key]: liftedValue,
      });
    }),
    Array.reduce({}, (acc, ctor) => ctor(acc)),
  ) as HKD<F, A>;
  return lifted;
};