How using funmake with strings



Hi,
I would like to bluid a function and call it.
for example:
aa(x):=block([],x*x);
d:funmake(concat("a","a"),[]);
ev(dd); /* gives aa(x) not x^2*/
aa(x); /* gives 4 -> OK */
d(2);
d evaluates to aa(x)
Improper name or value in functional position.
  -- an error.  Quitting.  To debug this try DEBUGMODE(TRUE);

Thank for your help and may be give me the good way  for building the 
name of functions online in my maxima script  in using the string

john