anchor.diff:    #- (or darwin linux)
     (error "XARGS-SEQUENCE is not supported on your operating system."))
   
  -(defun prepare-xargs-script (directory area tree program &key (if-exists :error))
  +(defun prepare-xargs-script (directory area tree program &key (if-exists :error if-exists-p))
     (declare (type (member :error :supersede :supersede-all) if-exists))
     (let ((program-path (if (listp program)
   			  (apply #'lisp-executable-pathname program)
  
positive.code: 	(error "Directory ~S already exists!" directory))
  
        (let ((*default-pathname-defaults* (parse-namestring pathspec)))
  	(let ((if-exists (if (eql if-exists :supersede-all) :supersede if-exists)))
  	  (write-program-data "xargs-data.sexp" area tree :if-exists if-exists)
  
  	  (with-open-file (out "xargs-program.sh" :if-exists if-exists :direction :output)
  
negative.code: 			 (namestring (merge-pathnames "xargs-data.sexp"))
  			 depth)))))
  	
  	(let ((if-exists (case if-exists
  			   (:supersede-all
  			    :supersede)
  			   (:supersede
  			    nil)
  			   (t
  			    (if if-exists-p
  				if-exists
  				:error)))))
  	  (with-open-file (out "xargs-arguments" :if-exists if-exists :direction :output)
  	    (when out
  	      (write-string *xargs-arguments-string* out)))
  