emacs align-regexp

Question

I'm looking for a way in emacs to format a code like this:

// param1, param2, param3, param4
foo(9, 8, "bar", 3)

to this:

//  param1, param2, param3, param4
foo(9,      8,      "bar",  3)

I guess it should be feasible with align-regexp but I have troubles to express the regexp to use in this case (actually I don't really understand what the regexp is supposed to match). Any idea?

Answer 1

With indent-tabs-mode set to nil¹, the following will do most of that:

C-uM-x align-regexp RET ,\(\s-*\) RET RET y

Dealing with the initial parameter is decidedly trickier. If you can guarantee the presence of a space after each comma, then you could use the following regexp along with 0 for the "Amount of spacing" question:

\(?:, \|^\(?://\|.*?(\)\)\(\s-*\)

You may prefer to use a two-step process, though. e.g.:

• ^\(?://\|.*?(\)\(\s-*\) with spacing = 0, and not repeating; followed by
• ,\(\s-*\) with spacing = 1, and repeating

You should probably elaborate on the kind of workflow you're looking for, though. Are you looking for a command to call manually? Automated alignment rules? Something to use occasionally via a keyboard macro? Other?

---

¹ I would recommend using the following in general:

;; Align with spaces only
(defadvice align-regexp (around align-regexp-with-spaces)
  "Never use tabs for alignment."
  (let ((indent-tabs-mode nil))
    ad-do-it))
(ad-activate 'align-regexp)