option.ts

const foo: number | undefined = 2

const inc: (x: number) => number = x => x + 1

const lift: <A, B>(f: (a: A) => B) => (a: A | undefined) => B | undefined =
    f => a => a === undefined
        ? undefined
        : f(a)

const map: <A, B>(a: A | undefined) => (f: (a: A) => B) => B | undefined =
        a =>
        f => a === undefined
            ? undefined
            : f(a)

const bar = map(foo)(inc)
const baz = lift(inc)(foo)