anchor.diff:  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                   By default, that file is created or superseded; this can be changed with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.
  +
  +IF-DOES-NOT-EXIST:  Can be :error, :create, nil,
  +                    or another value, equivalent to :CREATE for setf.
  +
   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))))
  
positive.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)))
  
  
  (defmacro with-io-syntax (&body body)
    ;; Leave the current package as-is.
  
negative.code:                                          (external-format :default))
    "
  NEW-CONTENTS:   A list of sexps.
  
  IF-DOES-NOT-EXIST:  Can be :error, :create, nil,
                      or another value, equivalent to :CREATE for setf.
  
  DO:             Writes the NEW-CONTENTS SEXPs readably into the file
                  at PATH.  By default, that file is created or
  