johnthecat

export type Lens<S, A> = (f: (y: A) => A, x: S) => S;

export const view = <S, A>(lens: Lens<S, A>) => (x: S) => {
  let value: unknown = null;
  lens(x => (value = x), x);
  // Because of lack of functor we can't create beautiful composition of .map.map... etc.,
  // so Const functor here is just plain variable without initializer
  return value as A;
};