table functions + user defined types

Ladies and Gentlemen,

Please, enlighten me, if you can, in the following matter:

I made a type:

create type my_type as (
a integer,
b integer
);

since I have a table:

create table my_table (
a integer;
);

and I have now a function too:

create or replace function my_func (
integer, -- a
integer, -- b
) returns setof my_type as
'
declare
pa alias for $1;
pb alias for $2;
-- declarations
my_value my_type;
begin
my_value.a := pa;
my_value.b := pb;
return my_value;
end;
' language 'plpgsql';

when I run this darling function I get a parse error pointing to the line after "begin".

What am I doing wrong? I have skimmed through all the manuals, had a look at the postgresql cookbook, no info on this. I just would like to have a function that returns more fields at the same time - add a column to table my_table, where I could occasionally return some value (e.g. error code). How to do this?

Thanks for your advice in advance

Zoltan Bartko