(define-syntax with
  (syntax-rules
    "use a context manager. Takes a value, name and body
     and binds value to name in body. Ensures resource cleanup.

     params:
      - val: the value to bind
      - var: the name to bind to
      - body: varargs for the body
     complexity: O(1)
     returns: the result of the resource cleanup" ()
    ((_ val var body ...)
      (let ((var val))
        (begin
          body ...
          (teardown var))))))

(defprotocol context-manager (teardown 1))
(defimpl context-manager input-port?  ((teardown close-input-file)))
(defimpl context-manager output-port? ((teardown close-output-file)))
(defimpl context-manager net:socket? ((teardown net:close-socket)))