Writing GNU Emacs Extensions

To What Is C-h Bound?

In order to find the symbol that names the Help command, we can use C-h b, which invokes another command called describe-bindings. This is one of the Help system's many subcommands. It presents a window listing all the keybindings in effect. Looking through it for the C-h binding, we find this line:

C-h          help-command

This tells us that help-command is the symbol that names the function that invokes Help.

Our Lisp example is almost complete, but we can't just write

(global-set-key "\M-?" help-command)       ;almost right!

This is wrong because of the way symbols are interpreted when they appear in Lisp expressions. If a symbol appears in the first position of a list, it's the name of a function to execute. If it appears elsewhere, it's a variable whose value needs to be retrieved. But when we run global-set-key as shown, we don't want the value contained in help-command, whatever that may be. The value we want is the symbol help-command itself. In short, we wish to prevent the symbol from being evaluated before it's passed to global-set-key. After all, as far as we know, help-command doesn't have a value as a variable.

The way to prevent a symbol (or any Lisp expression) from being evaluated is to quote it by preceding it with a single quote ('). It looks like this:

(global-set-key "\M-?" 'help-command)

Our Lisp example is now complete. If you place this line in your .emacs file, then M-? will invoke help-command the next time you run Emacs, and in all future Emacs sessions. ...