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Re: A value for "nothing"

From: Matt Wette
Subject: Re: A value for "nothing"
Date: Sun, 26 Aug 2018 15:08:07 -0700
User-agent: Mozilla/5.0 (X11; Linux x86_64; rv:52.0) Gecko/20100101 Thunderbird/52.9.1

On 08/26/2018 01:07 PM, Mark H Weaver wrote:

HiPhish <address@hidden> writes:

I am writing an implementation of MessagePack [1] for Guile and a part of the
spec is the presence of a "nil" data type. What would be a good value to
express "nothing" in Guile?

However, I would strongly advise against writing code (or worse, APIs)
that depend on (if #f #f) or *unspecified* returning a particular
distinguished value.

That tells me we should never use `(define x)'.

I would also avoid Guile's #nil.  That is a very special value, for one
purpose relating to Elisp compatibility, and ideally it should not be
used for anything else.

#nil only appears in the manual in association with the elisp extension.
I'm guessing it only intended to only appear in Scheme programs as '(const #nil)
when writing tree-il.

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