Token pasting/concatenation question

[Jon Drukman <jdrukman@xxxxxxxxx>]

I want to do the following:

#define API_URL(tail) @"http://localhost:2000/api/##tail";

#define URL_GET_USER_DATA API_URL(/get/user/data.json)

and then when I refer to URL_GET_USER_DATA later in the code, it should 
expand to @"http://localhost:2000/api/get/user/data.json";

I can not get "tail" to expand in the API_URL macro.  I've tried every 
combination of single and double pound signs.  (Well, every combination 
except for whatever the correct one is, obviously.)

gcc 4.0.1 on mac os X, trying to build an iPhone app in Objective-C.

Thanks for any help.
-jsd-