How to write unreadable Ceylon (see http://blog.ruslans.com/2014/12/seven-languages-in-seven-hours.html)

unreadable.ceylon

"Finds the (last) longest substring that contains
 at most two unique characters"
String longest2UniqueCharSubstring(String s)
        => let (init = [[0, 0, 0, 0], 0, '\0', '\0'],
                mpos = s.fold(init)((acc,ch)
                     => let ([[mb,me,cb,ce],cb1,ch0,ch1] = acc,
                             ce1 = ce+1,
                             max = (Integer b, Integer e) 
                                 => me-mb > e-b then [mb,me,b,e] 
                                                else [b,e,b,e])
                         if (ch==ch1) then [max(cb,ce1),cb1,ch0,ch1] 
                    else if (ch==ch0) then [max(cb,ce1),ce,ch1,ch]
                                      else [max(cb1,ce1),ce,ch1,ch])[0], 
                pos=mpos[0],
                len=mpos[1]-pos) 
           s[pos:len];