compose ts

type Incrementer = (x: number) => number;
const increment: Incrementer = x => x + 1;
console.assert(increment(2) == 3)


type Tostr = (x: number) => string;
const tostr: Tostr = (x: number) => `"${x}"`
console.assert(tostr(2) == `"2"`)

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 IncrNTostr = (x: number) => string
const incrNTostr: IncrNTostr = compose(tostr, increment)

console.assert(incrNTostr(5) == `"6"`)