Just for exploratory fun, I decided to see what it takes to write a prototypical object system in Lisp. Apparently its not much, I'm far from an experienced Lisper (barely fluent, if that) and I got it done in ~50 lines. A testament to Lisp's flexibility and expressiveness.

CL-USER> (load "/home/fitzgen/dev/protolith/protolith.lisp")
T
CL-USER> (in-package :protolith)
#<PACKAGE "PROTOLITH">
PROTOLITH> (defobj account ()
             (bal 0)
             (deposit (lambda (self x)
                        (funcall self 'set 'bal (+ (funcall self 'bal)
                                                   x)))))
ACCOUNT
PROTOLITH> (account 'bal)
0
PROTOLITH> (account 'deposit 50)
50
PROTOLITH> (account 'bal)
50
PROTOLITH> (defobj checking-account (account)
             (withdraw (lambda (self x)
                         (progn
                           (funcall self 'set 'bal (- (funcall self 'bal)
                                                      x))
                           x))))
CHECKING-ACCOUNT
PROTOLITH> (checking-account 'bal)
50
PROTOLITH> (checking-account 'withdraw 10)
10
PROTOLITH> (checking-account 'withdraw 10)
10
PROTOLITH> (checking-account 'bal)
30
PROTOLITH> (checking-account 'proto)
#<CLOSURE ACCOUNT>