Provide an align command for the haskell-mode

[PierreR]

Integrating something like the following would be a nice improvement (for those who don't want to bother with hindent)

The binding <space>m a could be used as it is the case in pupppet mode.

  (require 'align)
  ;; align rules
      (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))))

[gitfoxi]

Here is my favorite alignment plugin for vim:

https://github.com/junegunn/vim-easy-align

It is a mighty sword and not just for haskell (but also for haskell).

[d12frosted]

@PierreR Would you like to open PR for this?

[PierreR]

I know the code works fine but I am hesitant about making a PR because it is so haskell specific.

I guess I just need a confirmation that it is ok to add specific align rule such as these.

[d12frosted]

So you could add it into haskell layer 😄