How to check if a function (e.g. server-running-p) is available under Emacs?

问题

I'm trying to check if server-running-p is available in my .emacs file before calling it. I already have the following:

(if (not (server-running-p))
    (server-start))

But on some computers where I use Emacs, calling (server-running-p) gives an error because said call is not available. So I want to check if server-running-p is available before calling it. I thought boundp would do the try, but calling (boundp 'server-running-p) return nil even though the (server-running-p) call succeeds. What's the right way to check that calling server-running-p won't fail... or at least to suppress the error if said call fails. (And what kind of weird object is server-running-p anyway that boundp returns nil, but calling it succeeds?)

This is on Emacs 23.2.1, if it makes any difference.

---

Actually found the answer. You have to use fboundp for this instead of boundp, for some reason.

回答1:

boundp checks to see if a variable is bound. Since server-running-p is a function you'll want to use fboundp. Like so:

(if (and (fboundp 'server-running-p) 
         (not (server-running-p)))
   (server-start))

回答2:

A simpler way is to use "require" to make sure the server code is loaded. Here's what I use:

(require 'server)
(unless (server-running-p)
    (server-start))

回答3:

ryuslash’s suggestion was really helpful, but I modified it for my .emacs:

(unless (and (fboundp 'server-running-p)
             (server-running-p))
  (server-start))

This gets the server running even if server.el hasn't been loaded—server-running-p is only defined when server.el is loaded, and server-start is autoloaded.

来源：https://stackoverflow.com/questions/9999320/how-to-check-if-a-function-e-g-server-running-p-is-available-under-emacs