--- Begin Message ---
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Subject: |
[PATCH] doc: Document undefined?. |
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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
address@hidden {Scheme Procedure} undefined? x
+Return @code{#t} if @var{x} is undefined, else @code{#f}.
address@hidden deffn
@node Non-immediate objects
@subsubsection Non-immediate objects
--
2.15.1
--- End Message ---
--- Begin Message ---
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Subject: |
Re: bug#30145: [PATCH] doc: Document unspecified?. |
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Date: |
Sun, 21 Jan 2018 23:52:08 +0530 |
Mark H Weaver <address@hidden> 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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