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Date:         Mon, 20 Jul 2015 04:40:46 +0000
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From: Sean Allred <allred.sean@GMAIL.COM>
Subject: Re: expl3 boolean expressions: lazy evaluation
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Hi all,

If I might add my two cents:

I don't believe it's out of the question to wrap macro-parameters in some
sort of \bool_validate:n (if such a thing doesn't already exist) that would
run the checks and issue appropriate errors on a case-by-case basis. I
believe it's important to assume the programmer knows what he or she is
doing and let them account for this themselves. Otherwise, you introduce
complexity where none is needed for a large portion of folks.

Not to mention that it is just that much more to test and maintain.

-- 
Sean Allred

On Sun, Jul 19, 2015 at 11:30 PM Sean Allred <allred.sean@gmail.com> wrote:

> Hi all,
>
> If I might add my two cents:
>
> I don't believe it's out of the question to wrap macro-parameters in some
> sort of \bool_validate:n that would run the checks and issue appropriate
> errors on an on-demand basis. Assume the programmer knows what he or she is
> doing and let the programmer account for this on a case-by-case basis.
>
> -Sean Allred
>
> On Fri, Jul 17, 2015 at 9:07 AM Joseph Wright <
> joseph.wright@morningstar2.co.uk> wrote:
>
>> On 17/07/2015 15:00, Alexander Grahn wrote:
>> > Joseph,
>> >
>> > On Fri, Jul 17, 2015 at 12:09:27PM +0100, Joseph Wright wrote:
>> >> by
>> >>
>> >>    \bool_if:nTF
>> >>      {
>> >>        !\cs_if_exist:cTF {#1}
>> > really an `!' in front?
>> >
>> >> by
>> >>
>> >>    \bool_if:nT
>> >>      {
>> >>        ! \cs_if_exist:NTF \fxocg@insert@OC
>> > same here.
>> >
>> >> which could be redone as for the first case in media9. However,
>> >> reviewing the code I realise that as you have \use:c here you'll
>> >> actually get away with it (the second part will evaluate even if the
>> >> csname is undefined). If you do want a 'safe' change then
>> >>
>> >>    \bool_if:nTF
>> >>      {
>> >>        ! \cs_if_exist:cTF { OCGpdfobj#3 }
>> > same here.
>> >
>> > Alexander
>>
>> Indeed :-)
>>
>> I've tried to offer a 'minimal change' version of your code. To do that,
>> I've using the fact that \bool_if:nTF works by expansion. So
>>
>>     \bool_if:nTF
>>       {
>>          !\cs_if_exist:cTF {#1}
>>            ...
>>       }
>>
>> will find the "!" then expand what follows looking ultimately for
>> \c_true_bool or \c_false_bool. In the usual set up with something like
>> \cs_if_exist_p:c we have a function that will expand to one of these
>> outcomes. With \cs_if_exist:cTF that's not automatically the case but we
>> can put the logical outcomes into the T/F branches (as I did) to force
>> the same result.
>> --
>> Joseph Wright
>>
>

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<div dir=3D"ltr">Hi all,<br><br>If I might add my two cents:<br><br>I don&#=
39;t believe it&#39;s out of the question to wrap macro-parameters in some =
sort of \bool_validate:n (if such a thing doesn&#39;t already exist) that w=
ould run the checks and issue appropriate errors on a case-by-case basis. I=
 believe it&#39;s important to assume the programmer knows what he or she i=
s doing and let them account for this themselves. Otherwise, you introduce =
complexity where none is needed for a large portion of folks.<div><br></div=
><div>Not to mention that it is just that much more to test and maintain.</=
div><div><div><br></div><div>--=C2=A0</div><div>Sean Allred</div></div></di=
v><br><div class=3D"gmail_quote"><div dir=3D"ltr">On Sun, Jul 19, 2015 at 1=
1:30 PM Sean Allred &lt;<a href=3D"mailto:allred.sean@gmail.com">allred.sea=
n@gmail.com</a>&gt; wrote:<br></div><blockquote class=3D"gmail_quote" style=
=3D"margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex"><div>Hi =
all,<br><br>If I might add my two cents:<br><br>I don&#39;t believe it&#39;=
s out of the question to wrap macro-parameters in some sort of \bool_valida=
te:n that would run the checks and issue appropriate errors on an on-demand=
 basis. Assume the programmer knows what he or she is doing and let the pro=
grammer account for this on a case-by-case basis. <br></div><div><br>-Sean =
Allred</div><br><div class=3D"gmail_quote"><div dir=3D"ltr">On Fri, Jul 17,=
 2015 at 9:07 AM Joseph Wright &lt;<a href=3D"mailto:joseph.wright@mornings=
tar2.co.uk" target=3D"_blank">joseph.wright@morningstar2.co.uk</a>&gt; wrot=
e:<br></div><blockquote class=3D"gmail_quote" style=3D"margin:0 0 0 .8ex;bo=
rder-left:1px #ccc solid;padding-left:1ex">On 17/07/2015 15:00, Alexander G=
rahn wrote:<br>
&gt; Joseph,<br>
&gt;<br>
&gt; On Fri, Jul 17, 2015 at 12:09:27PM +0100, Joseph Wright wrote:<br>
&gt;&gt; by<br>
&gt;&gt;<br>
&gt;&gt;=C2=A0 =C2=A0 \bool_if:nTF<br>
&gt;&gt;=C2=A0 =C2=A0 =C2=A0 {<br>
&gt;&gt;=C2=A0 =C2=A0 =C2=A0 =C2=A0 !\cs_if_exist:cTF {#1}<br>
&gt; really an `!&#39; in front?<br>
&gt;<br>
&gt;&gt; by<br>
&gt;&gt;<br>
&gt;&gt;=C2=A0 =C2=A0 \bool_if:nT<br>
&gt;&gt;=C2=A0 =C2=A0 =C2=A0 {<br>
&gt;&gt;=C2=A0 =C2=A0 =C2=A0 =C2=A0 ! \cs_if_exist:NTF \fxocg@insert@OC<br>
&gt; same here.<br>
&gt;<br>
&gt;&gt; which could be redone as for the first case in media9. However,<br=
>
&gt;&gt; reviewing the code I realise that as you have \use:c here you&#39;=
ll<br>
&gt;&gt; actually get away with it (the second part will evaluate even if t=
he<br>
&gt;&gt; csname is undefined). If you do want a &#39;safe&#39; change then<=
br>
&gt;&gt;<br>
&gt;&gt;=C2=A0 =C2=A0 \bool_if:nTF<br>
&gt;&gt;=C2=A0 =C2=A0 =C2=A0 {<br>
&gt;&gt;=C2=A0 =C2=A0 =C2=A0 =C2=A0 ! \cs_if_exist:cTF { OCGpdfobj#3 }<br>
&gt; same here.<br>
&gt;<br>
&gt; Alexander<br>
<br>
Indeed :-)<br>
<br>
I&#39;ve tried to offer a &#39;minimal change&#39; version of your code. To=
 do that,<br>
I&#39;ve using the fact that \bool_if:nTF works by expansion. So<br>
<br>
=C2=A0 =C2=A0 \bool_if:nTF<br>
=C2=A0 =C2=A0 =C2=A0 {<br>
=C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0!\cs_if_exist:cTF {#1}<br>
=C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0...<br>
=C2=A0 =C2=A0 =C2=A0 }<br>
<br>
will find the &quot;!&quot; then expand what follows looking ultimately for=
<br>
\c_true_bool or \c_false_bool. In the usual set up with something like<br>
\cs_if_exist_p:c we have a function that will expand to one of these<br>
outcomes. With \cs_if_exist:cTF that&#39;s not automatically the case but w=
e<br>
can put the logical outcomes into the T/F branches (as I did) to force<br>
the same result.<br>
--<br>
Joseph Wright<br>
</blockquote></div></blockquote></div>

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