Re: What does #-3# mean?

[ludo@gnu.org (Ludovic Courtès)]

Hi,

Richard Shann <richard.shann@virgin.net> writes:

> I am displaying a structure that seems to be circular, and it shows
>
> (x_LIST . #-3#)
>
> x_LIST is my own symbol but what is the meaning of the other member of the pair?

Indeed, it means it’s a circular list:

--8<---------------cut here---------------start------------->8---
scheme@(guile-user)> (use-modules (srfi srfi-1))
scheme@(guile-user)> (circular-list 1 2 3)
$1 = (1 2 3 . #-2#)
scheme@(guile-user)> (circular-list 1)
$2 = (1 . #0#)
--8<---------------cut here---------------end--------------->8---

> And how does one track it down this notation in the guile manual? I am
> sure I came across this before, but cannot locate it in the manual
> (again?)

It doesn’t seem to be documented but you get the idea.  ;-)

Note that ‘read’ doesn’t understand it.

Thanks,
Ludo’.