Problem with function invocation

Hello.

When I create next function:

create function pilpot() returns integer as '
declare
foo integer;
begin
foo = insert into aviso(user) values(1);
return foo;
end;
' language 'plpgsql';

And try to invoque with:

# select pilpot();

I get next error:

ERROR: parser: parse error at or near "("

Where is the problem with this?

Thanks a lot.

David