/balance <account> 400
/overdraft <account> 100
/savings-rate <account> 0.1

/balance <savings-account> 0

$ account.balance
400

/withdraw <account> 100
-->
/balance <savings-account> 10
/balance <account> 290


/withdraw <account> 300
-->
/balance <savings-account> 40
/balance <account> -40

/withdraw <account> 100
-->
! Insufficient Funds !

/withdraw <account> 60
-->
/balance <account> -100
/balance <savings-account> 40

$ account.available-balance
60

--------------------------------------------------------------------------------

/available-balance= <account> _.balance + _.overdraft


/reaction= <account.withdraw> (/balance= <account> _.available-balance - $input)

/reaction.before= <account.withdraw>
  ($input > 0) False:(Error("Don't you want any money?"))

/reaction.before= <account.withdraw>
  (_.available-balance > 0) False:(Error("You're broke"))

/reaction.before= <account.withdraw>
  ((_.available-balance - $input) > 0) False:(Error("Insufficient Funds"))

/reaction.after <account.withdraw>
  Let('savings', ($input * _.savings-rate));
  ((_.available-balance - savings) > 0)
    True: ((/balance= <savings-account> _.balance + savings);
           (/balance= <account> _.balance - savings))

--------------------------------------------------------------------------------

/left <rect> 0
/top <rect> 0
/width <rect> 40
/height <rect> 10

/right= <rect> _.left + _.width
/bottom= <rect> _.top + _.height

/repr= <rect> "Rectangle((%s, %s), (%s, %s))" % (_.left, _.top, _.right, _.bottom)

/width <rect> 17

$ rect.repr
Rectangle(0, 0, 17, 10)

/left <rect> 25

$ rect.repr
Rectangle(25, 0, 42, 10)