A little JavaScript problem

README.md

Here is my TypeScript solution for A little JavaScript problem posted last year on Mishoo's blog

output.log

info > 1..3
log > 1
log > 2
log > 3

info > 1..10
log > 1
log > 2
log > 3
log > 4
log > 5
log > 6
log > 7
log > 8
log > 9
log > 10

info > 1..10 map pow
log > 1
log > 4
log > 9
log > 16
log > 25
log > 36
log > 49
log > 64
log > 81
log > 100

info > reverse 1..10 map pow
log > 100
log > 81
log > 64
log > 49
log > 36
log > 25
log > 16
log > 9
log > 4
log > 1

solution.ts

type Iteratee<T, R> = (head?: T, tail?: List<T>) => R;

type List<T> = <R>(fn: Iteratee<T, R>) => R

function Nil<R, T>(fn: Iteratee<T, R>) { return fn() }

const nil = <T>(): List<T> => Nil

const list = <T>(head: T, tail: List<T> = Nil): List<T> =>
    function List<R>(fn: Iteratee<T, R>): R { return fn(head, tail) }

const range = (start: number, end: number, acc = list(end)): List<number> =>
    end > start ? range(start, end - 1, list(end - 1, acc)) : acc

const foreach = <T>(listX: List<T>, fn: (item: T) => void): void => {
    if (listX !== Nil) {
        listX((head: T, tail: List<T>) => {
            fn(head)
            foreach(tail, fn)
        })
    }
}

const map = <T, R>(listX: List<T>, fn: (item: T) => R): List<R> =>
    listX === Nil ? Nil : listX((head: T, tail: List<T>) =>
        list(fn(head), map(tail, fn)))

const lhead = <T>(listX: List<T>): T | null | undefined =>
    listX === Nil ? null : listX(head => head)

const ltail = <T>(listX: List<T>): List<T> =>
    listX === Nil ? Nil : listX((__, tail) => tail) as List<T>

const reverse = <T, R>(listX: List<T>): List<R> => {
    const last = (_: List<T>) => lhead(reverse(_))
    const initial = (_: List<T>) => reverse(ltail(reverse(_)))

    return listX === Nil ? Nil : listX(
        (head: T, tail: List<T>) =>
            tail === Nil ? list(head) : list(
                last(tail),
                reverse(list(head, initial(tail)))
            ))
}

const tripod = list(1, list(2, list(3)))

console.info('1..3')
foreach(tripod, console.log.bind(console))

console.info('1..10')
foreach(range(1, 10), console.log.bind(console))

console.info('1..10 map pow')
const pow = (n: number) => n * n
foreach(map(range(1, 10), pow), console.log.bind(console))

console.info('reverse 1..10 map pow')
foreach(reverse(map(range(1, 10), pow)), console.log.bind(console))