index.ts

export interface Foldable<F, A> {
  reduce: (fn: (b: A, a: A) => A, initial: A, foldable: F) => A;
}

export const getArrayFold = <R, Q extends Array<R> = Array<R>>(): Foldable<Q, R> => {
  return {
    reduce: (fn, initial, array) => {
      return array.reduce(fn, initial);
    }
  };
};

getArrayFold<string>().reduce(
  (a, b) => a + b,
  '',
  ['hello', 'world']
);

getArrayFold<number>().reduce(
  (a, b) => a + b,
  0,
  [1, 2, 3]
);