A non-standard output library for C

This C program was an entry in [a contest organized by LinkedList NYC] (http://www.linkedlistnyc.org/archive/issue_083.html) for the most creative way to print a message.

#ifdef _ 

                      _(A)_(B)     _(C)_(D)  _(E)
                        _(F)     _(G) _(H) _(I)_(J)
                        _(K)      _(L) _(M)   _(N)
                        _(O)       _(P) _(Q)_(R)
                        _(S)         _(T) _(U)
                      _(V)_(W)         _(X)

                  _(Y)      _(Z)_(a) _(b)_(c) _(d)_(e)
                    _(f)      _(g)     _(h)    _(i)
                    _(j)_(k)  _(l)       _(m)_(n) 
                    _(o)  _(p)_(q)         _(r)  
                    _(s)      _(t)         _(u)
                  _(v)_(w)    _(x)       _(y)_(z)

#else
#define _(z)_##z)();typedef _##z(*
#include <stdio.h>
typedef int(*
#include __FILE__
#define __(_,z)_z _(__ y){return fputs(z,stdout),y?y(0):(_z)_0;}
#undef _
__)();__(_0,"")__(nl,"\n")__(_," ")
#define _(_)__(_,#_)
#include __FILE__

int main() {
  (L)(i)(n)(k)(e)(d)(L)(i)(s)(t)(_)(N)(Y)(C)(nl);

  return 0;
}

#endif

This program won the contest, and the organizers delivered the prize (ice cream) to my NYC friends.

You can read the analysis of how the program works.  The analysis is slightly incomplete though: can you determine the maximum length of the message this "library" supports?  (Hint: it is a function of the number of letters in the Latin alphabet.)