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>
Subject: bug#30145: closed (Re: bug#30145: [PATCH] doc: Document
 unspecified?.)
Date: Sun, 21 Jan 2018 18:23:02 +0000

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Your bug report

#30145: [PATCH] doc: Document undefined?.

which was filed against the guile package, has been closed.

The explanation is attached below, along with your original report.
If you require more details, please reply to 30145 <at> debbugs.gnu.org.

-- 
30145: http://debbugs.gnu.org/cgi/bugreport.cgi?bug=30145
GNU Bug Tracking System
Contact help-debbugs <at> gnu.org with problems

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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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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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