paredit-mode (http://www.emacswiki.org/emacs/ParEdit http://www.emacswiki.org/emacs/ParEdit) already provides a lot of functions for manipulating s-expressions,

paredit-mode (http://www.emacswiki.org/emacs/ParEdit http://www.emacswiki.org/emacs/ParEdit) already provides a lot of functions for manipulating s-expressions, including keeping track of your braces.