my-align.el

;;; my-align.el
;; Copyright (c) 2017 Bill Evans (r2evans)
;;
;; Author: Bill Evans
;; Created: 2017 Aug 03
;; Keywords: code align programming

;;; Commentary:
;; Simple wrapper wround 'align-regexp' with sane defaults.
;; Based on code first seen here
;;   https://stackoverflow.com/questions/3633120/emacs-hotkey-to-align-equal-signs
;; then extended to allow secondary alignment strings.

;; My preference is to assign it to `C-c =`, with
;;   (global-set-key (kbd "C-c =") 'align-to-equals)

;;; Usage:
;; - (default, no prefix) aligns on '='
;;    e.g., from R, starting with
;;
;;        list(
;;          short = 1000 - 1,
;;          longvariablename = 3 + 1415,
;;          another = 1 - 0
;;        )
;;        
;;    `C-c =`:
;;
;;        list(
;;          short            = 1000 - 1,
;;          longvariablename = 3 + 1415,
;;          another          = 1 - 0
;;        )
;;
;; - single prefix (C-u), user-defined alignment string
;;
;;    `C-u C-c =` then `-`:
;;        
;;        list(
;;          short            = 1000 - 1,
;;          longvariablename = 3 + 1415,
;;          another          = 1    - 0
;;        )
;;
;;    Note: user strings can be valid regexps, so a single period
;;    (e.g.) will need to be escaped as '\.' Instead of a simple '-',
;;    one could align on different characters with:
;;
;;    `C-u C-c =` then `[-+]` or
;;    `C-u C-c =` then `\(-\|+\|_\|:::\)`:
;;        
;;        list(
;;          short            = 1000 - 1,
;;          longvariablename = 3    + 1415,
;;          another          = 1    - 0
;;        )

;;; Code:
(defun align-to-equals (prefix)
  "Align region to equal signs"
  (interactive "p")
  (let ((ch (if (= prefix 1)
                "="
              (read-from-minibuffer "Indent on string: ")))
        (begin (region-beginning))
        (end (region-end))
        )
    (message (concat "Indenting on: '" ch "'"))
    (align-regexp begin end (concat "\\(\\s-*\\)" ch) 1 1 ))
  )

;; works in R and python, likely others, so keep it global
(global-set-key (kbd "C-c =") 'align-to-equals)

;;; my-align.el ends here