Greenspun's Tenth Rule states:
Any sufficiently complicated C or Fortran program contains an ad hoc, informally-specified, bug-ridden, slow implementation of half of Common Lisp.
Which is why it brought a smile to my face to see the following while diging through the PostgreSQL sources:
#define NIL ((List *) NULL)
... and later on:
extern List *lcons(void *datum, List *list);
Unfortunately, car, cdr, cadr, caadr, caaadr and their ilk were nowhere to be found.
For those of who are a little confused, cons is used to construct a linked list in the various dialects of Lisp, while nil is generally the value of the next pointer at then end of such a linked list. The inference that can be drawn from the above facts is: whoever designed Postgres's linked list implementation probably modeled it on the linked lists provided in a Lisp environment.