Emacs Lisp函数用于在4和8之间切换变量'tab-width'

The source tree that I work on has files indented with different tab values, (not to mention spaces) and the best I can do is to set emacs to use the style found in the region of code I am modifying. Instead of doing M-x set-variable tab-width to 4 or 8, a key binding to toggle the tab-width among these two value would help immensely.The source tree that I work on has files indent