anchor.diff:                                      (if-exists :supersede)
                                       (external-format :default))
     "
  +oIF-DOES-NOT-EXIST:  Can be :error, :create, nil,
  +                    or another value, equivalent to :CREATE for setf.
  +
   DO:     Writes the NEW-CONTENTS SEXP readably into the file at PATH.  By default,
           that file is created or superseded; this can be changed with
           the keyword IF-DOES-NOT-EXIST or IF-EXISTS.
  +
   RETURN: The NEW-CONTENTS, or if-exists or if-does-not-exist in case of error.
   "
     (with-open-file (out path :direction :output
  -                            :if-does-not-exist if-does-not-exist
  +                            :if-does-not-exist (output-file-if-does-not-exist if-does-not-exist)
                               :if-exists if-exists
                               :external-format external-format)
       (if (and (streamp out) (not (or (eq out if-exists)  (eq out if-does-not-exist))))
           (with-io-syntax
  -            (write new-contents :stream out))
  +          (write new-contents :stream out))
           out)))
   
   
  
positive.code: DO:             Store the NEW-CONTENTS, into the file at PATH, each string on a line.
                  By default, that file is created or superseded; this can be changed with
                  the keyword IF-DOES-NOT-EXIST or IF-EXISTS.
  NEW-CONTENT:    A sequence of strings, none of them should contain #\newline,
                  otherwise the mapping between strings and file lines won't be
                  conserved.
  RETURN:         The NEW-CONTENTS or if-exists or if-does-not-exist in case of error.
  "
    (with-open-file (out path :direction :output
                         :if-does-not-exist if-does-not-exist
                         :if-exists if-exists
                         :external-format external-format)
      (if (and (streamp out) (not (or (eq out if-exists)  (eq out if-does-not-exist))))
  
negative.code: (defmacro with-input-file ((streamvar path element-type if-does-not-exist external-format) &body body)
    `(call-with-input-file ,path ,element-type ,if-does-not-exist ,external-format (lambda (,streamvar) ,@body)))
  
  (defun output-file-if-does-not-exist (if-does-not-exist)
    (case if-does-not-exist
      ((:error :create nil) if-does-not-exist)
      (otherwise :create)))
  (declaim (inline output-file-if-does-not-exist))
  
  (defmacro with-io-syntax (&body body)
    ;; Leave the current package as-is.
  