"Set SESSION's value of PARAMETER to VALUE.

SESSION nil means use the current session.

Return value."

  (let ((session (or session (wg-current-session))))

    (wg-set-parameter (wg-session-parameters session) parameter value)

    (setf (wg-session-modified session) t)

    value))

(defun wg-remove-session-parameter (session parameter)

  "Remove parameter PARAMETER from SESSION's parameters."

  (let ((session (or session (wg-current-session))))

    (wg-asetf (wg-session-parameters session) (wg-aremove it parameter))

    (setf (wg-session-modified session) t)))

(defun wg-session-local-value (variable &optional session)

  "Return the value of VARIABLE in SESSION.

SESSION nil defaults to the current session.  If VARIABLE does

not have a session-local binding in SESSION, the value is

resolved by Emacs."

  (let* ((undefined (cl-gensym))

         (value (wg-session-parameter session variable undefined)))

    (if (not (eq value undefined)) value

      (symbol-value variable))))

(defun wg-reset-frame (frame)

  (set-frame-parameter frame 'wg-workgroup-state-table nil)

  (set-frame-parameter frame 'wg-current-workgroup-uid nil)

  (set-frame-parameter frame 'wg-previous-workgroup-uid nil))

(defun wg-save-session-on-exit (behavior)

  "Perform session-saving operations based on BEHAVIOR."

  (cl-case behavior

    (ask (wg-query-and-save-if-modified))

    (save

     (if (wg-determine-session-save-file-name)

         (wg-save-session)

       (wg-query-and-save-if-modified)))))

(defun wg-save-frames ()

  "Save opened frames as a session parameter.

Exclude `selected-frame' and daemon one (if any).

http://stackoverflow.com/questions/21151992/why-emacs-as-daemon-gives-1-more-frame-than-is-opened"

  (interactive)

  (let ((fl (frame-list)))

    (mapc (lambda (frame)

            (if (string-equal "initial_terminal" (terminal-name frame))

                (delete frame fl))) fl)

    (setq fl (delete (selected-frame) fl))

    (if (wg-current-session t)

        (wg-set-session-parameter (wg-current-session t)

                                  'frame-list

                                  (mapcar 'wg-frame-to-wconfig fl)))))