GnuplotMode

First check out if “gnuplot.el” is part of your (X)Emacs distribution.

(Focus are the information that where hard to find for me)

Notice:

a.) On MS-WIN32 operating systems the directory delimiter is the backslash, but to use it inside a string you have to decorate it, “\” becomes “\\”.

b.) My gnuplot is vulnerable against whitespaces at the end of a line, especially if I want to continue a command in the next line, so I looked for a tool that can show different types of whitespaces, I found the library `whitespace.el’.

c.) Sorry I’m not an elisp expert.

Here comes a part of my .xinit.el (I have only XEmacs installed on a MS-WIN32 computer):

[...]
;;;; ====  Configure `whitespace.el'  ====
   (require 'whitespace)
   
;;; add `gnuplot-mode' to the list `whitespace-modes'
  (setq whitespace-modes (cons 'gnuplot-mode whitespace-modes))

;;; Enable whitespace globally
;; To check (and possibly fix if `whitespace-auto-cleanup' is set) whitespace
;; problems automatically on new buffers, you can turn
;; `whitespace-global-mode' on.
  (setq whitespace-global-mode t)
  
;;; Check buffer with `whitespace' every time you open a file:
;; To enable that add `whitespace-write-file-hook' to the `find-file-hooks':
;; add this to check for whitespace, if a file is opened (the file had been found):
   (add-hook 'find-file-hooks 'whitespace-write-file-hook)

;;; Check buffer with `whitespace' before you save the file:
;; To check (and possibly fix if `whitespace-auto-cleanup' is set) whitespace
;; problems automatically but only when saving buffers, you can add the
;; function `whitespace-write-file-hook' to your `write-file-hooks'.
   (add-hook 'write-file-hooks 'whitespace-write-file-hook)

;;; Configure behaviour of `whitespace':
;; define which white spaces should be visuable
  (setq whitespace-style '(trailing newline tab-mark newline-mark))

;; Global variable to check `whitespace' at `end-of-line'
  (setq whitespace-check-ateol-whitespace t)
;; leave alone leading whitespace
  (setq whitespace-check-leading-whitespace nil)

[...]

;;;; ====  Configure Gnuplot-mode  ====
;; these lines enable the use of gnuplot mode
  (autoload 'gnuplot-mode "gnuplot" "gnuplot major mode" t)
  (autoload 'gnuplot-make-buffer "gnuplot" "open a buffer in gnuplot mode" t)

;; this line automatically causes all files with the .gp extension to
;; be loaded into gnuplot mode
  (setq auto-mode-alist
     (append
        (list
           '("\\.gp$" . gnuplot-mode)
           '("\\.plt$" . gnuplot-mode)
        )
      auto-mode-alist))

;; if you have the latest win32 version of gnuplot
(add-hook 'gnuplot-load-hook
                   '(lambda ()
                        (setq gnuplot-program
                              "C:\\Programme\\gnuplot\\bin\\pgnuplot.exe")
                        (setq gnuplot-gnuplot-buffer "plot.plt") ; name of a new gnuplot file
                        ; (setq show-trailing-whitespace t)
                        (setq whitespace-check-buffer-ateol t)
                    ))
[...] 

(Sorry I did not found the way for a linebreak here in the wiki)