functs maybe option

type Composer = <A, B, C> (
    f: (x: B) => C,
    g: (x: A) => B,
) => (x: A) => C
const compose: Composer = (f, g) => x => f(g(x))

type Option<A> = Some<A> | None
interface Some<A> {
    _tag: 'Some',
    value: A
}
interface None {
    _tag: 'None'
}

const some = <A>(x: A): Option<A> => ({ _tag: 'Some', value: x })
const none: Option<never> = {_tag: 'None'}

const isNone = <A>(x: Option<A>): x is None => x._tag === 'None'

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

type Div2 = (x: number) => Option<number>
const div2: Div2 = x => x === 0 ? none : some(2/x)

const composed = compose(
    (x: Option<number>) => isNone(x) ? none : some(inc(x.value)),
    div2
)

console.log(composed(4))
console.log(composed(0))