[R] Simple example of using a closure in R to manage bank accounts?

[Michael Hannon]

Greetings.  I once ran across a simple (toy) example of using a closure in R to 
manage bank accounts.  I've got a use for it now but can no longer find it.  If 
you have it (or a similar example), will you please send it to me?  
(Unfortunately, a web search that includes the terms "bank" and "closure" leads 
into a whole pile of unrelated stuff.)

Thanks,

-- Mike