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Re: What does #-3# mean?

From: Ludovic Courtès
Subject: Re: What does #-3# mean?
Date: Tue, 24 Aug 2010 18:38:02 +0200
User-agent: Gnus/5.13 (Gnus v5.13) Emacs/23.2 (gnu/linux)


Richard Shann <address@hidden> 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.


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