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(at)stolaf(dot)edu | stopped a free thought" --Charles Ives