Generating GRANT/REVOKE on functions from catalog

I am attempting to script the generation of grant/revoke statements for
a database, and I'm having some trouble when it comes to functions.

consider the following function:

create function add(a integer, b integer)
returns integer
as $$
select $1 + $2;
$$ language SQL;

The statement I need to generate is:

revoke all on function public.add(integer, integer) from someuser;

I'm attempting to use the pg_proc table in the system catalogs, and I'm
good up to the point where I need the parameter types.  Can anyone give
me a hand with this?

Thanks,

--
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*Doug Gorley* | doug.gorley@gmail.com <mailto:doug.gorley@gmail.com>