How to make @id or $id as parameter name in plpgsql, is it available?

Hello, pgsql-hackers

Can I change postgresql's source to make the following plpgsql works ?
If could, would you please tell me where can i change the source?
I want to try it.

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CREATE FUNCTION users_select_by_id(@id int4)
RETURNS SETOF users_set
AS '

declare rec record;

begin
for rec in    select * from users where id = @idloop    return next rec;end loop;return;

end; 'LANGUAGE plpgsql;
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Thanks & Regards

Arnold.Zhu
2000-11-23