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I want to enforce only one GUI instance for Emacs, so I want to check if at least one GUI frame is open or not (i.e. the frame that is open with emacsclient -c), and ignore the ones opened in Terminal. How do I do that? I already tried visible-frame-list function but this seems to count all frames.

  • frame-list returns a list of all live frames and frame-visible-p returns if a frame is visible – eflanigan00 Mar 8 '17 at 4:39
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You can use the framep function to determine the type of each frame. It returns a symbol describing the type of the frame: t for terminal, x for X window, w32 for MS windows, ns for Mac/GNUstep, and pc for a direct-write MS-DOS frame.

Once you have this you could count the number of (say) X Window frames with something like (length (seq-filter (lambda (f) (eq (framep f) 'x)) (frame-list))), or for a function that returns t if there is an X Window frame otherwise nil, use (seq-some (lambda (f) (eq (framep f) 'x)) (frame-list)). There are many other variations as well :-)

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Use the display-graphic-p function:

display-graphic-p is a compiled Lisp function in `frame.el'.

(display-graphic-p &optional DISPLAY)

Return non-nil if DISPLAY is a graphic display. Graphical displays are those which are capable of displaying several frames and several different fonts at once. This is true for displays that use a window system such as X, and false for text-only terminals. DISPLAY can be a display name, a frame, or nil (meaning the selected frame's display).

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