aggregate functions and varchar type

I am having trouble with the following aggregate function (in postgres
6.4.2):

create aggregate nlappend ( basetype = varchar, sfunc1 = nl_strappend, stype1 = varchar, initcond1 = ''
);

When I try to define it, I get "parse error at or near varchar".
(nl_strappend is a function of two varchar arguments that returns a
varchar).  Defining an aggregate function on other types works fine.  

Is it possible to define an aggregate function on the varchar type?  If
so, what am I doing wrong?

Please reply via private email; I will summarize replies and followup to
the list.




thanks,
wb

---
Will Benton        | "A black eye never reformed a drunkard; a czar never 
bentonw@stolaf.edu |  stopped a free thought"              --Charles Ives