Redux Reducer + morphic-ts

SafeReducer.ts

import { Reducer, Action } from "redux";
import { ADT } from '@morphic-ts/adt';

export const safeReducer = <A extends Action, S, tag extends keyof A & string>(
  curriedReducer: (a: A) => (s: S) => S,
  defaultState: S,
  adt: ADT<A, tag>
): Reducer<S, A> => (
  nullableState,
  action
) => {
  if (!nullableState || !adt.verified(action)) return defaultState;
  return curriedReducer(action)(nullableState);
}