Square root function using continuations

sqrt_callcc.ss

;; sqrt function using continuations
;;
;; a port from an example in the first Scheme memo (AIM-349)
;; to modern Scheme

(define sqrt
  (lambda (x epsilon)
    ((lambda (ans looptag)
       (call-with-current-continuation
        (lambda (returntag)
          (begin
            (set! looptag (call-with-current-continuation (lambda (k) k)))
            (if (< (abs (- (* ans ans) x)) epsilon)
                (returntag ans)
                #f)
            (set! ans (/ (+ (/ x ans) ans) 2))
            (looptag looptag)))))
     1.0
     #f)))

;; "Anyone who doesn't understand how this manages to work 
;; probably should not attempt to use CATCH" (Sussman & Steele, AIM-349)