How to GRANT SELECT on all tables?

Another noobish question.

I'm looking for the "moral equivalent" of the mythical

  GRANT SELECT ON TABLE * TO PUBLIC

I.e. I'm looking for a way to grant SELECT privileges to PUBLIC on all
the tables, without having to specify all the table names.

Naively, I tried the subquery approach

  GRANT SELECT
    ON TABLE (SELECT tablename FROM pg_tables WHERE schemaname='public')
    TO PUBLIC

but this failed too.

Thanks!

kj