anchor.diff:      (posix-write fd (make-array 1 :initial-element byte :element-type '(unsigned-byte 8)))))
   
   (defmacro with-fd-streams (() &body body)
  +  "Evaluate `body' in an environment where the standard streams are
  +bound to `fd-stream's.
  +
  +`*standard-input*', `*standard-output*', and `*error-output*' are
  +bound to symbolic `fd-stream's for fds 0, 1, and 2 respectively."
     `(let ((*standard-input* (make-instance 'fd-character-input-stream :fd 0 :symbolic t))
            (*standard-output* (make-instance 'fd-character-output-stream :fd 1 :symbolic t))
            (*error-output* (make-instance 'fd-character-output-stream :fd 2 :symbolic t)))
        ,@body))
   
   (defun make-binary-fd-stream (fd direction symbolic)
  +  "Create a binary `fd-stream'."
     (macrolet
         ((make (type)
            `(make-instance ',type :symbolic symbolic :fd fd)))
  
positive.code:         result))))
  
  (defun fd-stream-unread (stream thing)
    (with-slots (buffer buffer-offset) stream
      (when (zerop buffer-offset)
        (error "Can't unread without reading first"))
  
negative.code:         (error 'invalid-fd :fd fd))))
    fd)
  
  (defun %simplify-fd-bindings (fd-bindings new-fd-fn)
    "Transform the given bindings so that there is no overlap between
  fds that will be bound in the child process and the source fds in this
  process.
  