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Date:         Mon, 29 Apr 2013 11:50:10 -0700
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From: scott heard <scott.heard@GMAIL.COM>
Subject: Re: Behaviour of \SplitArgument with missing input
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Hello, forgive (and correct) me if I misunderstand how this command should
be used:

  \DeclareDocumentCommand { \foo }
    { > { \SplitArgument { 2 } { ; } } m }
    { \my_command:nnn #1 }

As the output of '\SplitArgument' is some number of brace groups lumped
together into a '#1', it seems like a test for '-NoValue' would need to be
moved into '\my_command:nnn', i.e. from the xparse interface, into
"programmer code".  As `\IfNoValueTF' is an xparse command, that doesn't
feel correct.  If this is a reasonable interpretation/usage, then my
personal opinion would be that empty brace groups (or something else) would
be preferable to -NoValue-'s.
scott


On Mon, Apr 29, 2013 at 1:54 AM, Joseph Wright <
joseph.wright@morningstar2.co.uk> wrote:

> Hello all,
>
> I've had a couple of reports recently of an inconsistency in the way
> \SplitArgument is documented compared to how it is implemented. In the
> current CTAN release, something like
>
>   \DeclareDocumentCommand { \foo }
>     { > { \SplitArgument { 2 } { ; } } m }
>     { \showtokens {#1} }
>   ...
>   \foo{bar}
>
> gives
>
>     > {bar}{-NoValue-}{-NoValue-}.
>     \foo code #1->\showtokens {#1}
>
> i.e. inserts the '-NoValue-' marker, but the documentation says you
> should get
>
>     > {bar}{}{}.
>     \foo code #1->\showtokens {#1}
>
> i.e. empty groups.
>
> In the SVN, I have altered the behaviour to do what the docs say.
> However, this breaks some packages and more importantly may not be the
> 'best' approach. In particular, returning '-NoValue-' allows
> differentiation of
>
>    \foo{bar;;} and \foo{bar}
>
> which is not possible if an empty group is returned.
>
> Conceptually, '-NoValue-' was introduced for flagging omitted optional
> arguments. Using it in \SplitArgument is therefore something of an
> extension, but at the same time the way this function works makes the
> splitting 'optional'. Thus it is quite arguable that the use of the
> special marker is entirely correct here.
>
> What do people feel is the best approach?
>
> (Note: There are some other issues related to '-NoValue-' that this
> raises, which I'll cover in a separate message.)
> --
> Joseph Wright
>

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<div dir=3D"ltr">Hello, forgive (and correct) me if I misunderstand how thi=
s command should be used:<div><br></div><div><span style=3D"font-family:ari=
al,sans-serif;font-size:13px">=A0 \DeclareDocumentCommand { \foo }</span><b=
r style=3D"font-family:arial,sans-serif;font-size:13px">
<span style=3D"font-family:arial,sans-serif;font-size:13px">=A0 =A0 { &gt; =
{ \SplitArgument { 2 } { ; } } m }</span><br style=3D"font-family:arial,san=
s-serif;font-size:13px"><span style=3D"font-family:arial,sans-serif;font-si=
ze:13px">=A0 =A0 { \my_command:nnn #1 }</span></div>
<div><font face=3D"arial, sans-serif"><br></font></div><div><font face=3D"a=
rial, sans-serif">As the output of &#39;\SplitArgument&#39; is some number =
of brace groups lumped together into a &#39;#1&#39;, it seems like a test f=
or &#39;-NoValue&#39; would need to be moved into &#39;\my_command:nnn&#39;=
, i.e. from the xparse interface, into &quot;programmer code&quot;. =A0As `=
\IfNoValueTF&#39; is an xparse command, that doesn&#39;t feel correct. =A0I=
f this is a reasonable interpretation/usage, then my personal opinion would=
 be that empty brace groups (or something else) would be preferable to -NoV=
alue-&#39;s.</font></div>
<div><font face=3D"arial, sans-serif">scott<br></font><div><br></div><div><=
br></div></div></div><div class=3D"gmail_extra"><br><br><div class=3D"gmail=
_quote">On Mon, Apr 29, 2013 at 1:54 AM, Joseph Wright <span dir=3D"ltr">&l=
t;<a href=3D"mailto:joseph.wright@morningstar2.co.uk" target=3D"_blank">jos=
eph.wright@morningstar2.co.uk</a>&gt;</span> wrote:<br>
<blockquote class=3D"gmail_quote" style=3D"margin:0 0 0 .8ex;border-left:1p=
x #ccc solid;padding-left:1ex">Hello all,<br>
<br>
I&#39;ve had a couple of reports recently of an inconsistency in the way<br=
>
\SplitArgument is documented compared to how it is implemented. In the<br>
current CTAN release, something like<br>
<br>
=A0 \DeclareDocumentCommand { \foo }<br>
=A0 =A0 { &gt; { \SplitArgument { 2 } { ; } } m }<br>
=A0 =A0 { \showtokens {#1} }<br>
=A0 ...<br>
=A0 \foo{bar}<br>
<br>
gives<br>
<br>
=A0 =A0 &gt; {bar}{-NoValue-}{-NoValue-}.<br>
=A0 =A0 \foo code #1-&gt;\showtokens {#1}<br>
<br>
i.e. inserts the &#39;-NoValue-&#39; marker, but the documentation says you=
<br>
should get<br>
<br>
=A0 =A0 &gt; {bar}{}{}.<br>
=A0 =A0 \foo code #1-&gt;\showtokens {#1}<br>
<br>
i.e. empty groups.<br>
<br>
In the SVN, I have altered the behaviour to do what the docs say.<br>
However, this breaks some packages and more importantly may not be the<br>
&#39;best&#39; approach. In particular, returning &#39;-NoValue-&#39; allow=
s<br>
differentiation of<br>
<br>
=A0 =A0\foo{bar;;} and \foo{bar}<br>
<br>
which is not possible if an empty group is returned.<br>
<br>
Conceptually, &#39;-NoValue-&#39; was introduced for flagging omitted optio=
nal<br>
arguments. Using it in \SplitArgument is therefore something of an<br>
extension, but at the same time the way this function works makes the<br>
splitting &#39;optional&#39;. Thus it is quite arguable that the use of the=
<br>
special marker is entirely correct here.<br>
<br>
What do people feel is the best approach?<br>
<br>
(Note: There are some other issues related to &#39;-NoValue-&#39; that this=
<br>
raises, which I&#39;ll cover in a separate message.)<br>
--<br>
Joseph Wright<br>
</blockquote></div><br></div>

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