anchor.diff:  ;;;;AUTHORS
   ;;;;    <PJB> Pascal J. Bourguignon <pjb@informatimago.com>
   ;;;;MODIFICATIONS
  +;;;;    2021-05-12 <PJB> Corrected handling of :if-does-not-exist <value> for SETF functions.
   ;;;;    2018-08-18 <PJB> Added create-file.
   ;;;;    2014-10-22 <PJB> Factorized out file reader functions, handle if-does-not-exist non-nil values.
   ;;;;    2009-07-27 <PJB> Renamed TEXT-FILE-TO-STRING-LIST to STRING-LIST-TEXT-FILE-CONTENTS,
  
positive.code:                                     (if-exists :supersede)
                                      (external-format :default))
    "
  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          that file is created or superseded; this can be changed with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-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))
          out)))
  
  
  
negative.code:                                     (external-format :default))
    "
  RETURN: The NEW-CONTENTS, or if-exists or if-does-not-exist in case of error.
  
  DO:     Store the NEW-CONTENTS 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          that file is created or superseded; this can be changed with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.
  
  NEW-CONTENT:  A sequence of ELEMENT-TYPE.
  
  IF-DOES-NOT-EXIST:  Can be :error, :create, nil,
                      or another value, equivalent to :CREATE for setf.
  "
    (with-open-file (out path :direction :output
                         :if-does-not-exist (output-file-if-does-not-exist if-does-not-exist)
                         :if-exists if-exists
                         :element-type element-type
                         :external-format external-format)
  