Closures

gistfile1.txt

** Scheme **
(define makeaccount
    (lambda (balance)
        (lambda (amt)
            (begin (set! balance (+ balance amt))
                balance))))


<==>

** JavaScript **
var makeAccount = function(balance) {
    return function(amt) {
        balance += amt;     // since balance is in the local scope, this function will close around it
        return balance;     // even though it hasn't been assigned to a var (see jsfiddle.net/6g5U6).
    };
};