Re: Proposal to use JSON for Postgres Parser format

On Tue, Sep 20, 2022 at 4:03 PM Thomas Munro <thomas(dot)munro(at)gmail(dot)com> wrote:
> On Tue, Sep 20, 2022 at 3:58 PM Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> wrote:
> > Thomas Munro <thomas(dot)munro(at)gmail(dot)com> writes:
> > > FWIW, it derives from Lisp s-expressions, but deviates from Lisp's
> > > default reader/printer behaviour in small ways, including being case
> > > sensitive and using {NAME :x 1 ...} instead of #S(NAME :x 1 ...) for
> > > structs for reasons that are lost AFAIK (there's a dark age between
> > > the commit history of the old Berkeley repo and our current repo, and
> > > it looks like plan nodes were still printed as #(NAME ...) at
> > > Berkeley).
> >
> > Wow, where did you find a commit history for Berkeley's code?
> > There's evidence in the tarballs I have that they were using
> > RCS, but I never heard that the repo was made public.
>
> One of the tarballs at https://dsf.berkeley.edu/postgres.html has the
> complete RCS history, but Stas Kelvich imported it to github as Peter
> G has just reported faster than I could.

To explain my earlier guess: reader code for #S(STRUCTNAME ...) can
bee seen here, though it's being lexed as "PLAN_SYM" so perhaps the
author of that C already didn't know that was a general syntax for
Lisp structs. (Example: at a Lisp prompt, if you write (defstruct foo
x y z) then (make-foo :x 1 :y 2 :z 3), the resulting object will be
printed as #S(FOO :x 1 :y 2 :z 3), so I'm guessing that the POSTGRES
Lisp code, which sadly (for me) was ripped out before even that repo
IIUC, must have used defstruct-based plans.)

https://github.com/kelvich/postgres_pre95/blob/master/src/backend/lib/lispread.c#L132

It may still be within the bounds of what a real Lisp could be
convinced to read though, given a reader macro to handle {} and maybe
some other little tweaks here and there.