How do I reference named parameters in Postgres sql functions?

Postgres noobie here.

I'm trying to convert a SQL Server stored proc into a Postgres function. Currently cannot figure out how to turn this SQL line into Postgres.

SQL Server:

input: @name = null

SELECT *
FROM table
WHERE name = ISNULL(@name, name)

Postgres:

input: n = null

SELECT *
FROM table
WHERE name = COALESCE(n, name)

I'm getting the error "column n does not exist." How do I reference parameters in select statements in Postgres functions?

UPDATE:

Definition of Postgres function

CREATE OR REPLACE FUNCTION fn_name (n VARCHAR(32) = NULL, name OUT varchar(32), description OUT varchar(64))
RETURNS setof record
AS 
$$
    SELECT u.name
        , u.description
    FROM table_a u
    WHERE u.name = COALESCE(n, u.name);

$$
LANGUAGE sql;