Emacs Yasnippet for Different Coding Styles

Just recently started using yasnippet for emacs and really like the way it works, however I've run into a minor nuisance I'd like some help to solve if possible.

One snippet I like in particular is the "for"-snippet, i.e.:

# -*- mode: snippet -*-
# name: for
# key: for
# --
for (${1:i = 0}; ${2:i < N}; ${3:i++}) {
    $0
}

However I recently started working on a project where we have a different coding style. Simply put the snippet above would be changed to place the starting brace position to:

# -*- mode: snippet -*-
# name: for
# key: for
# --
for (${1:i = 0}; ${2:i < N}; ${3:i++})
{
    $0
}

I would however like to easily switch between different projects and consequently between different coding styles without having to manually change the snippets or create many duplicates. So I figured it should be possible to write some elisp code in the snippet to automatically adapt to the currently active coding style.

Looking around at some of the Emacs/elisp documentation, I found the so called c-hanging-brace-alist (GNU doc) which I feel I should be able to use somehow. However I have never really done any programming in elisp, and I'm not really sure how to accomplish this. Any help or advice would be appreciated!

Solution

Here is a suggestion:

Define a variable to hold the current coding style:
```
(setq current-coding-style 'default)
```

Define a command to toggle between the default style and the style used in your new project, and bind it to a key sequence of your choosing:

(defun toggle-coding-style ()
  (interactive)
  (if (eq current-coding-style 'default)
      (setq current-coding-style 'special)
    (setq current-coding-style 'default)))

(global-set-key (kbd "C-c t") 'toggle-coding-style) ;; Replace C-c t 
                                                    ;; with another binding
                                                    ;; if you like

Define a function that places the opening brace according to the coding style that is currently "active":
```
(defun place-brace ()
  (if (eq current-coding-style 'default) " {" "\n{"))
```
Replace the opening brace in the for snippet with a call to this function (as explained here, arbitrary Elisp code can be embedded into snippets by enclosing it in backquotes):
```
# -*- mode: snippet -*-
# name: for
# key: for
# --
for (${1:i = 0}; ${2:i < N}; ${3:i++})`(place-brace)`
    $0
}
```

With this in place all you need to do to switch between coding styles (and corresponding snippet expansions) is press C-c t.