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18 Aligning code

Select a region you want to align text within, M-x align-regexp, and type a regexp representing the alignment delimiter.

For example, I often line up my Haddock comments: 

f :: a -- ^ does a
  -> Foo b -- ^ and b
  -> c -- ^ to c

Select the region, and let the regexp be ‘--’: 

f :: a     -- ^ does a
  -> Foo b -- ^ and b
  -> c     -- ^ to c

Of course, this works for just about anything. Personally, I’ve globally bound it to C-x a r: 

(global-set-key (kbd "C-x a r") 'align-regexp)

Note that you can also just use the rules below for telling the aligner about Haskell. Once you evaluate this, you can just use M-x align, which I like to bind to M-[. 

(add-to-list 'align-rules-list
             '(haskell-types
               (regexp . "\\(\\s-+\\)\\(::\\|∷\\)\\s-+")
               (modes quote (haskell-mode literate-haskell-mode))))
(add-to-list 'align-rules-list
             '(haskell-assignment
               (regexp . "\\(\\s-+\\)=\\s-+")
               (modes quote (haskell-mode literate-haskell-mode))))
(add-to-list 'align-rules-list
             '(haskell-arrows
               (regexp . "\\(\\s-+\\)\\(->\\|→\\)\\s-+")
               (modes quote (haskell-mode literate-haskell-mode))))
(add-to-list 'align-rules-list
             '(haskell-left-arrows
               (regexp . "\\(\\s-+\\)\\(<-\\|←\\)\\s-+")
               (modes quote (haskell-mode literate-haskell-mode))))