lazy

stream.js

var noop = [];

function stream(arr){
    if(arr.length === 0) return noop;
    return cons(function (){return arr[0]}, function (){ return stream(arr.slice(1))})
}

function cons(head, tail){
    return [head, tail];
}

function nil(stream) {
    return stream === noop;
}

function force(obj) {
    if (typeof obj === 'function') {
        return obj();
    }
    return obj;
}

function head(stream) {
    return (stream[0] = force(stream[0]));
}

function tail(stream) {
    return (stream[1] = force(stream[1]));
}

function foldr(stream, fn, z) {
    if (nil(stream)) return z;
    else {
        return fn(head(stream), function () {
            return foldr(tail(stream), fn, z);
        });
    }
}

function foldl(stream, fn, init) {
    var result = init;
    while (!nil(stream)) {
        result = fn(result, head(stream))
        stream = tail(stream);
    }
    return result
}

function take(stream, n){
    return foldr(stream, function (a, rest) {
        return function (n) {
            if (n <= 0) return noop;
            return cons(a, force(rest)(n-1));
        };
    }, function () { return noop; })(n);
}

function drop(stream, n){
    while (n-->0) {
        stream = tail(stream);
    }
    return stream;
}

function some(stream, fn){
    return foldr(stream, function(a,rest){
        return fn(a) || a();
    }, false)
}

const num = n => cons(() => n, () => num(n+1));

function sum(stream) {
    return foldr(stream, function(a, b) {
        return a + force(b);
    }, 0);
}


console.log(take(drop(num(0), 1000000), 1))