> as remote from one another as Postgres procedures and custom Lisps must be in every other respect.

Just a fun fact: Parts of postgres (before the SQL days, I think) used to be in lisp. To this day we still have some weird function/macro names stemming from those (e.g. lcons).

  * Once upon a time, parts of Postgres were written in Lisp and used real
  * cons-cell lists for major data structures.  When that code was rewritten
  * in C, we initially had a faithful emulation of cons-cell lists, which
  * unsurprisingly was a performance bottleneck.  A couple of major rewrites
  * later, these data structures are actually simple expansible arrays;
  * but the "List" name and a lot of the notation survives.