Sqlup.el : the story of the minor mode that could – Short intro to me – Friendly manual to this talk

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Trevoke

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Sqlup.el : the story of the minor mode that could – Short intro to me – Friendly manual to this talk

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sqlup-talk

Diving into emacs lisp by following the trail left by sqlup-mode.el

On Github Trevoke / sqlup-talk

Sqlup.el : the story of the minor mode that could

Or, how Ι stopped worrying and learned to love emacs

Because, why spend five minutes doing something you can spend ten years automating?

Short intro to me

I'm Aldric Giacomoni in meatspace

I'm Trevoke in cyberspace

Find me at trevoke@gmail.com

I study martial arts (the relevance will soon dawn upon you)

Emacs and me

Because everyone's origin story can be instructive

  • college
  • Rubymine
  • vim
  • emacs

Friendly manual to this talk

If you're just reading the slides, you'll see emacs functions. Just use C-h <function-name> in emacs and seize the power.

Short intro to modes

  • One major mode
  • Many minor modes

The simplest minor mode

(define-minor-mode miyagi-mode
  "Teaches you martial arts without you even knowing it"
  (if miyagi-mode
      (message "Wax on")
    (message "Wax off")))

How sqlup started

  • There is a Right Way™ to write SQL
  • I'm SO lazy
  • Can't emacs do EVERYTHING?

Enter The Friend

Oh sure, you just need a keyword list and you look back and see if the word is in the list.

— Eric Jones

At this point, I knew exactly nothing of emacs-lisp.

Implementation for v1

This version took over the space and open-parens keys, and replaced the last word (emacs symbol, really) with its upcased counterpart if it was found in a list.

message

It's Ye Olde Friendly Logger 

(message "Hello, world!")

thing-at-point

It returns the kind of thing… at point… that you specify 

(thing-at-point 'symbol)

bounds-of-thing-at-point

A cons cell with the buffer position for …

Start and end of… Thing… At point… 

(bounds-of-thing-at-point 'symbol)

interactive

This function is used to tell emacs that you're writing an extended command (M-x miyagi) 

(defun miyagi ()
  (interactive)
  (message "Show me… Paint the fence!"))

The meat of it

(setq current-word-upcase (upcase (thing-at-point 'symbol)))
(setq current-word-boundaries (bounds-of-thing-at-point 'symbol))
(delete-region
  (car current-word-boundaries)
  (cdr current-word-boundaries))
(insert current-word-upcase)

Flaws with v1

  • insert operates out of the event loop
(insert "(")
  • limited matching capability (just strings)

"Batch mode"

I added a function to capitalize SQL keywords in a region.

while

(while
    true
  (message "Oh good, a `while true` loop."))

search-forward-regexp

With replace-match 

(search-forward-regexp "[[:alpha:]_]+" (point-max))
(replace-match "Miyagi!")

save-excursion

;; In Okinawa, belt mean no need rope to hold up pants.
(save-excursion
  (goto-char (point-min))
  (while (search-forward-regexp "rope" (point-max) t)
  (replace-match "belt")))

Implementation for v2

Now sqlup uses a post-command hook, working directly with emacs' event loop.

post-command-hook

;; The fourth argument means "buffer-local" if non-nil
(add-hook 'post-command-hook 'do-something nil t)

Arguable choice. Runs ALL THE TIME. So, early guard clauses are imperative. 

(defun sqlup-should-do-work-p ()
  (or (sqlup-user-pressed-return-p)
      (and (sqlup-user-is-typing-p)
           (sqlup-trigger-self-insert-character-p))))

this-command-keys-vector

(defun sqlup-user-pressed-return-p ()
  (equal 13 (elt (this-command-keys-vector) 0)))

symbol-name with this-command 

(defun sqlup-user-is-typing-p ()
  (string= "self-insert-command" (symbol-name this-command)))

Oh yeah, also leverage sql-mode !

(sql-add-product-keywords 'ansi '())

Required tweaks for v2

Pull the correct keywords from sql-mode 

(defun sqlup-find-correct-keywords ()
  (if (and (boundp 'sql-mode-font-lock-keywords)
           sql-mode-font-lock-keywords)
      (mapcar 'car sql-mode-font-lock-keywords)
    (mapcar 'car (sql-add-product-keywords
                  (or (and (boundp 'sql-product) sql-product)
                      'ansi) '()))))

Lesson learned

This looks so simple NOW. 

(defun sqlup-maybe-capitalize-last-symbol ()
  (forward-symbol -1)
  (sqlup-work-on-symbol-at-point))

Lesson learned

Wait, emacs can do WHAT? 

(defun sqlup-comment-p (line)
  (nth 4 (syntax-ppss)))

Trust me. Write down syntax-ppss and look it up.

syntax-ppss..

Okay, so if you've looked up syntax-ppsss...

Its behavior hinges on the current major mode.

So .... V3, coming next ........ Is a hack

V3?! emacs is SO POWERFUL!

Here's the hack. 

(defun sqlup-capitalizable-p (point-location)
  (let ((old-buffer (current-buffer)))
    (with-temp-buffer
      (insert-buffer-substring old-buffer)
      (sql-mode)
      (goto-char point-location)
      (and (not (sqlup-commentp))
           (not (sqlup-stringp))))))

This is the implementation I'm most ashamed of. Mostly because I've received no feedback from emacs hackers on it yet.

v .. 3.5 ? redis

I got a request for redis-mode support.

Luckily, redis-mode provides a list of keywords.

Ze Code

(defun sqlup-find-correct-keywords ()
  (cond ((sqlup-redis-mode-p) (mapcar 'downcase redis-keywords))
        ((sqlup-within-sql-buffer-p) (mapcar 'car sql-mode-font-lock-keywords))
        (t (mapcar 'car (sql-add-product-keywords
                         (or (and (boundp 'sql-product) sql-product)
                             'ansi) '())))))

(defun sqlup-redis-mode-p ()
  (string= (with-current-buffer (current-buffer) major-mode)
           "redis-mode"))

What about tests?

I AM SO EXCITED BECAUSE I GOT SOME TESTS WORKING LAST WEEK!

Yeah, sqlup is two years old, so I'm batting a thousand.

Links

Thanks!

Sqlup.el : the story of the minor mode that could Or, how Ι stopped worrying and learned to love emacs Because, why spend five minutes doing something you can spend ten years automating?