Getting list of supported types in Postgres

Hi guys,

I am looking for a way to get list of supported types in Postgres
together with information whether type can have optional size (like
varchar for example), whether it can have precision (like decimal for
example), and whether it can come as value of sequence (like all integer
types for example), but I have trouble getting that info from pg_type
table. This is SQL I was using:

select
    pg_catalog.format_type(oid, null),
    *
from
    pg_type
where
    typnamespace = (select oid from pg_namespace where
nspname='pg_catalog') and
    typisdefined and
    typname not like '$_%' escape '$' and
    typname not like 'pg%' and
    typtype = 'b'
order by
    typname

apparently pg_catalog.format_type for some types return quoted name
("char" for example), also I can't find decimal in results (there is
numeric, but I would like to have complete list of supported types, so
decimal should be included too). In documentation it is said that typlen
of -1 or -2 means that type is variable length, but I don't know how to
find out if type can have additional precision?

Regards,
Ivan