Assign a function to a variable, and invoke it

[troelskn <troelskn@gmail.com>]

I'm trying to assign an existing function to a variable, so I can call
that variable, rather than the actual function directly. The aim is to
have a single point, where I can change behaviour for my module. The
code I have so far is:

(defvar my-browse-url 'browse-url)
...
(my-browse-url "http://example.com")

I suppose that functions and variables have different namespaces in
elisp? How do I invoke the function, which my-browse-url points to?