popup-forward-backward.el

(require 'cl)

(defgroup popup-forward-backward nil
  "Minor mode for popping up lines which surround forward/backward point")

(defcustom popup-forward-backward:idle-delay 5
  "Number of seconds of idle time to wait before popping up"
  :type 'number
  :group 'popup-forward-backward)

(define-minor-mode popup-forward-backward-mode
  "Minor mode for popping up lines which surround forward/backward point"
  :lighter " PFB"
  :init-value nil
  :group popup-forward-backward
  :global nil
  (if popup-forward-backward-mode
      (popup-forward-backward:enable)
      (popup-forward-backward:disable)))

(defun popup-forward-backward:turn-on ()
  (interactive)
  (popup-forward-backward-mode 1))

(defvar popup-forward-backward:idle-timer nil)

(defvar popup-forward-backward:open-tokens '("(" "{" "[" "<"))
(defvar popup-forward-backward:close-tokens '(")" "}" "]" ">"))
(defvar popup-forward-backward:forward 'forward-sexp)
(defvar popup-forward-backward:backward 'backward-sexp)
(defvar popup-forward-backward:lines 1)

(defun popup-forward-backward:enable ()
  (make-local-variable 'popup-forward-backward:open-tokens)
  (make-local-variable 'popup-forward-backward:close-tokens)
  (make-local-variable 'popup-forward-backward:forward)
  (make-local-variable 'popup-forward-backward:backward)
  (make-local-variable 'popup-forward-backward:lines)
  (add-hook 'post-command-hook 'popup-forward-backward:run-idle-timer))

(defun popup-forward-backward:disable ()
  (remove-hook 'post-command-hook 'popup-forward-backward:run-idle-timer))

(defun popup-forward-backward:run-idle-timer ()
  (when (timerp popup-forward-backward:idle-timer)
    (cancel-timer popup-forward-backward:idle-timer))
  (when popup-forward-backward-mode
    (setq popup-forward-backward:idle-timer
          (run-with-idle-timer popup-forward-backward:idle-delay
                               t
                               'popup-forward-backward
                               ))))

(defun popup-forward-backward ()
  "popup 1+`lines'*2 lines"
  (interactive)
  (cond
    ((find (string (char-before)) popup-forward-backward:close-tokens
           :test 'string-equal)
     (popup-backward popup-forward-backward:lines))
    ((find (string (char-after)) popup-forward-backward:open-tokens
           :test 'string-equal)
     (popup-forward popup-forward-backward:lines))))

(defun popup-forward (lines)
  (let ((text (save-excursion
               (call-interactively popup-forward-backward:forward)
               (unless (and  (<= (window-start) (point))
                             (< (point) (window-end)))
                 (popup-forward-backward:get-lines lines)))))
    (when text
      (popup-tip text))))

(defun popup-backward (lines)
  (let ((text (save-excursion
               (call-interactively popup-forward-backward:backward)
               (unless (and  (<= (window-start) (point))
                             (< (point) (window-end)))
                 (popup-forward-backward:get-lines lines)))))
    (when text
      (popup-tip text))))

(defun popup-forward-backward:get-lines (lines)
  (let ((beg (save-excursion (ignore-errors (previous-line lines))
                             (line-beginning-position)))
        (end (save-excursion (ignore-errors (next-line lines))
                             (line-end-position))))
    (buffer-substring beg end)))