lisp newbie help

if i set the value of a symbol to a function, how do i call it with that symbol?

(setq a #'append)
(a ... ) <--how do i do this?

thanks

What was the real reason for an arbitrary number of namespaces in those lisps anyway? It looks to be related to pre-von Neumann concerns. The idea of having the privilege of a list variable inside a list function looks stupid. You end up with N setters and N ways to get things... Even C doesn't do this (though C does have separate namespaces for things like structs, but those don't form valid operations much with functions and variables except through things like sizeof).