GNU bug report logs - #30145
[PATCH] doc: Document undefined?.

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From: help-debbugs <at> gnu.org (GNU bug Tracking System)
To: Arun Isaac <arunisaac <at> systemreboot.net>
Cc: tracker <at> debbugs.gnu.org
Subject: bug#30145: closed ([PATCH] doc: Document undefined?.)
Date: Sun, 21 Jan 2018 18:23:02 +0000

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Your message dated Sun, 21 Jan 2018 23:52:08 +0530
with message-id <cu7po63ysvj.fsf <at> systemreboot.net>
and subject line Re: bug#30145: [PATCH] doc: Document unspecified?.
has caused the debbugs.gnu.org bug report #30145,
regarding [PATCH] doc: Document undefined?.
to be marked as done.

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From: Arun Isaac <arunisaac <at> systemreboot.net>
To: bug-guile <at> gnu.org
Cc: Arun Isaac <arunisaac <at> systemreboot.net>
Subject: [PATCH] doc: Document undefined?.
Date: Wed, 17 Jan 2018 23:22:04 +0530

* doc/ref/data-rep.texi: Document undefined?.
---
 doc/ref/data-rep.texi | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/doc/ref/data-rep.texi b/doc/ref/data-rep.texi
index bb7f74afe..ed3a5a522 100644
--- a/doc/ref/data-rep.texi
+++ b/doc/ref/data-rep.texi
@@ -470,6 +470,9 @@ check to see if @var{x} is @code{SCM_UNBOUND}.  History will not be kind
 to us.
 @end deftypefn
 
+@deffn {Scheme Procedure} undefined? x
+Return @code{#t} if @var{x} is undefined, else @code{#f}.
+@end deffn
 
 @node Non-immediate objects
 @subsubsection Non-immediate objects
-- 
2.15.1

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From: Arun Isaac <arunisaac <at> systemreboot.net>
To: Mark H Weaver <mhw <at> netris.org>
Cc: 30145-done <at> debbugs.gnu.org
Subject: Re: bug#30145: [PATCH] doc: Document unspecified?.
Date: Sun, 21 Jan 2018 23:52:08 +0530

Mark H Weaver <mhw <at> netris.org> writes:

About undefined?: That was a typo. I mentioned that in a later message.

> It's nonsensical to ask whether a given object is "unspecified".  When
> the Scheme standards say that the result of a computation is an
> unspecified value, that means that *any* Scheme object could be
> returned.
>
> In Guile, for historical reasons, we usually return a particular object
> SCM_UNSPECIFIED (a.k.a. *unspecified*) in cases where the specification
> says that the result is unspecified.  However, we make no promises that
> this will remain the case in future versions of Guile.
>
> The number of legitimate uses for 'unspecified?' is extremely small.  In
> fact, I can think of only one: when a REPL prints the result of a user's
> computation, it is nice to avoid printing "*unspecified*" and instead
> print nothing in that case.
>
> In almost every other case, use of 'unspecified?' implies an assumption
> that it's possible to detect when a value is an "unspecified" value,
> when in fact that is fundamentally impossible.
>
> What do you think?

I agree. I didn't put very much thought into the matter before I sent
the patch. I needed unspecified? for a patch to GNU Guix. I found the
info documentation missing for unspecified? and thought I'll write
it. Later, it turned out unspecified? was not necessary for the Guix
patch after all. But, I had already documented unspecified?. So, I sent
it here.

Anyways, I'll close this bug report.

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