;http://groups.google.com/group/comp.lang.functional/msg/2fde5545c6657c81

  (define-syntax do
       (syntax-rules (def)
         ((do (v <- expr) rest) (bind expr (lambda (v) rest)))
         ((do expr)             expr)
         ((do expr expr)        (bind (set expr) (lambda (dummy) expr)))
         ((do expr expr* ...)   (do expr (do expr* ...))))) 

 This emulates Haskell's do-notation, which we can use as
     follows:

     (define (number-tree tree)
        (if (pair? tree)
            (do (left-subtree <- (number-tree (car tree)))
                (right-subtree <- (number-tree (cdr tree)))
                (unit (cons left-subtree right-subtree)))
            (do (n <- get)
                (set (+ n 1))
                (unit n))))

     Cool, huh?