I did it too. It is not too hard - there was not a agreement on syntax.
can be nice some like CTE
WITH PROCEDURE x(a int, b int) AS ... $$ SELECT x(10);
I've seen "WITH function...." syntax in Oracle (here's an example: https://oracle-base.com/articles/12c/with-clause-enhancements-12cr1) , but I can see where we'd run into trouble with SELECT statements being atomic, and the PROCEDURE being transactional. If we only allowed a one-line SELECT that problem would go away, but that raises the question of whether SELECT is the right keyword for the job. Is there something in the SQL standard for that?
Either way, we're clearly talking about something to add to postgres, not psql itself, and we should split this conversation to another thread. Sorry for hijacking your thread, Pierre.