"Dependently-typed" JS thing

gistfile1.js

// Syntax note: optionally whitespace-sensitive, \ is an alias for function,
// and -> at the end of a function means return the last value.
// Haskell-style (operator), which is implicit if an operator is the only
// argument to a function.

// The return value of a type function is compared to the value put in,
// and if they are === it type checks.
function Int(n) -> Math.floor(n)

function add(a: Int, b: Int) -> a + b

function Addable(value) -> value + value.constructor()

function add(a: Addable, b: Addable) -> a + b

function TypedArray(type) ->
    function (value) -> value.every(\e -> type(e) === e)) ? value : NaN

function sum(array: TypedArray(Addable)) -> array.reduce(+)