It would give users even more flexibility if they had the capability not only to explicitly define the location of the gnuplot 'data' file ( http://common-lisp.net/pipermail/clnuplot-devel/2009-February/000008.html) but to also have the capability to explicitly specify the location of the rendered (graphical) version of the chart/plot.
Something like
(defun fullname-rendered (plot type) (let ((fullpath (fullpath plot))) (namestring (make-pathname ;; strip type info :name (pathname-name fullpath) :directory (pathname-directory fullpath) :type type))))
and then a modification of each 'set output' line for gnuplot (in the various WRITE-PLOT definitions) to something like
(format out "set output '~A'~C" (fullname-rendered plot "ps") #\Linefeed))
seems like it would do the trick...
- Alan