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Inspecting objects at point with ESS

Somewhere in the second half of last year I switched my primary text editor from Vim to Emacs. Calm down! I use Evil. So, one of my primary languages is R and I was in love with this plugin in Vim. A snippet of my vim config that I used to rely heavily on in Vim was:

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map <LocalLeader>nr :call RAction("rownames")<CR>
map <LocalLeader>nc :call RAction("colnames")<CR>
map <LocalLeader>n2 :call RAction("names")<CR>
map <LocalLeader>nn :call RAction("dimnames")<CR>
map <LocalLeader>nd :call RAction("dim")<CR>
map <LocalLeader>nh :call RAction("head")<CR>
map <LocalLeader>nt :call RAction("tail")<CR>
map <LocalLeader>nl :call RAction("length")<CR>
map <LocalLeader>cc :call RAction("class")<CR>

These commands were invented by me after looking at a similar usage pattern in the plugin’s manuals. Being able to inspect objects at point without switching from my editor to the R prompt made me much more productive than when I could not do this. After I switched to Emacs and the mighty ESS for programming in R, replicating this was an explicit TODO in my ESS configuration. Ladies & gentlemen, today I bring you the solution. Drumroll!

The primary idea — ess-command wrapped with popup-tip — came from this blog post of yore and was wielded to magnificent effect by yours truly. (Yes, I’m a megalomaniac, thank you very much.)

Lemme show you teh codez.

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;;; Show a popup by executing arbitrary commands on object at point.
;;; Inspiration:
;;; blogisticreflections.wordpress.com/2009/10/01/r-object-tooltips-in-ess/

;; emacs.stackexchange.com/questions/696/get-content-of-a-buffer
(defun asb-read-into-string (buffer)
  (with-current-buffer buffer
    (buffer-string)))

(defun asb-ess-R-object-popup (r-func)
  "R-FUNC: The R function to use on the object.
Run R-FUN for object at point, and display results in a popup."
  (let ((objname (current-word))
        (tmpbuf (get-buffer-create "**ess-R-object-popup**")))
    (if objname
        (progn
          (ess-command (concat "class(" objname ")\n") tmpbuf)
          (let ((bs (asb-read-into-string tmpbuf)))
            (if (not(string-match "\(object .* not found\)\|unexpected" bs))
                (progn
                  (ess-command (concat r-func "(" objname ")\n") tmpbuf)
                  (let ((bs (asb-read-into-string tmpbuf)))
                    (popup-tip bs)))))))
  (kill-buffer tmpbuf)))

(defun asb-ess-R-object-popup-str ()
  (interactive)
  (asb-ess-R-object-popup "str"))

(defun asb-ess-R-object-popup-interactive (r-func)
  (interactive "sR function to execute: ")
  (asb-ess-R-object-popup r-func))

(evil-leader/set-key-for-mode 'ess-mode "ei" 'asb-ess-R-object-popup-str)
(evil-leader/set-key-for-mode 'ess-mode "eI"
  'asb-ess-R-object-popup-interactive)

The function asb-ess-R-object-popup allows us to yank the word at point and execute an arbitrary function on it (without arguments) and display the output as a popup-tip. This function is wrapped into asb-ess-R-object-popup-str mapped to <leader>ei (evil-ess-inspect) to inspect the str of the object interactively because this is what I use the most. Another function called asb-ess-R-object-popup-interactive mapped to <leader>eI (evil-ess-interactive-inspect) asks the user what R function to inspect the object with. Common suspects will be head, tail, names, etc. You know the drill. Have a look at the video and pay attention to the minibuffer.

PS: Actually, don’t bother watching the video; I don’t know why youtube insists on downgrading the video quality.