How to check if buffer or block has content

How to check if buffer or block has content

[Benjamin Buchmuller via ntg-context]

Hi,

How can I check if a buffer or block has content (or is empty) before a \useblocks or \getbuffer statement?

I would like to typeset a headline only if the buffer/block has been used in a particular section and want to avoid headlines with empty sections.

Thanks!


Benjamin
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Re: How to check if buffer or block has content

[Aditya Mahajan via ntg-context]

On Mon, 2 Aug 2021, Benjamin Buchmuller via ntg-context wrote:

> Hi,
> 
> How can I check if a buffer or block has content (or is empty) before a \useblocks or \getbuffer statement?
> 
> I would like to typeset a headline only if the buffer/block has been used in a particular section and want to avoid headlines with empty sections.

There may be more efficient ways to do it (since buffers are stored at the lua end), but you can always do \doiftextelse(\getbuffer[...]} to test it buffer creates any output.

Aditya
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Re: How to check if buffer or block has content

[Hans Hagen via ntg-context]

On 8/2/2021 4:43 PM, Aditya Mahajan via ntg-context wrote:
> On Mon, 2 Aug 2021, Benjamin Buchmuller via ntg-context wrote:
> 
>> Hi,
>>
>> How can I check if a buffer or block has content (or is empty) before a \useblocks or \getbuffer statement?
>>
>> I would like to typeset a headline only if the buffer/block has been used in a particular section and want to avoid headlines with empty sections.
> 
> There may be more efficient ways to do it (since buffers are stored at the lua end), but you can always do \doiftextelse(\getbuffer[...]} to test it buffer creates any output.
indeed you know there is a way ...

\starttext

\startbuffer[test]
test
\stopbuffer

\doifelsebuffer{test} {YES} {NOP}

\permanent\protected\def\doifelsebuffercontent#1%
   {\doifelse{\luaexpr{(string.strip(buffers.getcontent("#1")) ~= "" and 
"yes")}}{yes}}

\startbuffer[test]
\stopbuffer

\doifelsebuffercontent{test} {YES} {NOP}

\startbuffer[test]

\stopbuffer

\doifelsebuffercontent{test} {YES} {NOP}

\stoptext

if we can agree on a proper name then i can add a (more efficient) 
\doifelse...

Hans


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                                           Hans Hagen | PRAGMA ADE
               Ridderstraat 27 | 8061 GH Hasselt | The Netherlands
        tel: 038 477 53 69 | www.pragma-ade.nl | www.pragma-pod.nl
-----------------------------------------------------------------
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Re: How to check if buffer or block has content

[Hans van der Meer via ntg-context]

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And in pathological cases where even this does not work (as I encountered a few days ago): 
\setbox\scratchbox=\vboxx{content}\ifdim\wd\scratchbox>\zeropoint .. \else .. \fi
dr. Hans van der Meer


> On 2 Aug 2021, at 17:17, Hans Hagen via ntg-context <ntg-context@ntg.nl> wrote:
> 
> On 8/2/2021 4:43 PM, Aditya Mahajan via ntg-context wrote:
>> On Mon, 2 Aug 2021, Benjamin Buchmuller via ntg-context wrote:
>>> Hi,
>>> 
>>> How can I check if a buffer or block has content (or is empty) before a \useblocks or \getbuffer statement?
>>> 
>>> I would like to typeset a headline only if the buffer/block has been used in a particular section and want to avoid headlines with empty sections.
>> There may be more efficient ways to do it (since buffers are stored at the lua end), but you can always do \doiftextelse(\getbuffer[...]} to test it buffer creates any output.
> indeed you know there is a way ...
> 
> \starttext
> 
> \startbuffer[test]
> test
> \stopbuffer
> 
> \doifelsebuffer{test} {YES} {NOP}
> 
> \permanent\protected\def\doifelsebuffercontent#1%
>  {\doifelse{\luaexpr{(string.strip(buffers.getcontent("#1")) ~= "" and "yes")}}{yes}}
> 
> \startbuffer[test]
> \stopbuffer
> 
> \doifelsebuffercontent{test} {YES} {NOP}
> 
> \startbuffer[test]
> 
> \stopbuffer
> 
> \doifelsebuffercontent{test} {YES} {NOP}
> 
> \stoptext
> 
> if we can agree on a proper name then i can add a (more efficient) \doifelse...
> 
> Hans
> 
> 
> -----------------------------------------------------------------
>                                          Hans Hagen | PRAGMA ADE
>              Ridderstraat 27 | 8061 GH Hasselt | The Netherlands
>       tel: 038 477 53 69 | www.pragma-ade.nl | www.pragma-pod.nl
> -----------------------------------------------------------------
> ___________________________________________________________________________________
> If your question is of interest to others as well, please add an entry to the Wiki!
> 
> maillist : ntg-context@ntg.nl / http://www.ntg.nl/mailman/listinfo/ntg-context
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> wiki     : http://contextgarden.net
> ___________________________________________________________________________________


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Re: How to check if buffer or block has content

[Wolfgang Schuster via ntg-context]

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Hans van der Meer via ntg-context schrieb am 02.08.2021 um 18:21:
> And in pathological cases where even this does not work (as I 
> encountered a few days ago):
> \setbox\scratchbox=\vboxx{content}\ifdim\wd\scratchbox>\zeropoint .. 
> \else .. \fi

This is how \doiftext works but it uses a \hbox.

Wolfgang


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Re: How to check if buffer or block has content

[Wolfgang Schuster via ntg-context]

Hans Hagen via ntg-context schrieb am 02.08.2021 um 17:17:
> On 8/2/2021 4:43 PM, Aditya Mahajan via ntg-context wrote:
>> On Mon, 2 Aug 2021, Benjamin Buchmuller via ntg-context wrote:
>>
>>> Hi,
>>>
>>> How can I check if a buffer or block has content (or is empty) 
>>> before a \useblocks or \getbuffer statement?
>>>
>>> I would like to typeset a headline only if the buffer/block has been 
>>> used in a particular section and want to avoid headlines with empty 
>>> sections.
>>
>> There may be more efficient ways to do it (since buffers are stored 
>> at the lua end), but you can always do \doiftextelse(\getbuffer[...]} 
>> to test it buffer creates any output.
> indeed you know there is a way ...
>
> \starttext
>
> \startbuffer[test]
> test
> \stopbuffer
>
> \doifelsebuffer{test} {YES} {NOP}
>
> \permanent\protected\def\doifelsebuffercontent#1%
>   {\doifelse{\luaexpr{(string.strip(buffers.getcontent("#1")) ~= "" 
> and "yes")}}{yes}}
>
> \startbuffer[test]
> \stopbuffer
>
> \doifelsebuffercontent{test} {YES} {NOP}
>
> \startbuffer[test]
>
> \stopbuffer
>
> \doifelsebuffercontent{test} {YES} {NOP}
>
> \stoptext
>
> if we can agree on a proper name then i can add a (more efficient) 
> \doifelse...

To follow the existing commands we can use

\doifelsebufferempty
\doifelsebuffersomething
\doifelsebuffernothing

or (we already have \xmldoif... and \btxdoif...)

\bufferdoifelseempty
\bufferdoifelsesomething
\bufferdoifelsenothing

Wolfgang

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Re: How to check if buffer or block has content

[Hans Hagen via ntg-context]

On 8/2/2021 6:31 PM, Wolfgang Schuster via ntg-context wrote:

> \doifelsebufferempty

i go for that one (mkiv and lmtx0 ; btw, \doifelsebuffer is expandable 
but the empty test not)

Hans

-----------------------------------------------------------------
                                           Hans Hagen | PRAGMA ADE
               Ridderstraat 27 | 8061 GH Hasselt | The Netherlands
        tel: 038 477 53 69 | www.pragma-ade.nl | www.pragma-pod.nl
-----------------------------------------------------------------
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Re: How to check if buffer or block has content

[Benjamin Buchmuller via ntg-context]

Wow, that's powerful!

I'll add the wiki entries later tonight. 

Thanks a lot!

> On Aug 3, 2021, at 17:02, Hans Hagen <j.hagen@xs4all.nl> wrote:
> 
> On 8/2/2021 8:54 PM, Benjamin Buchmuller via ntg-context wrote:
>> That's great, I wikified a Note for testing if a buffer exists or has content (using the \getbuffer[…] approach for the moment).
>> If I was asked, I'd opt for \doifelseemptybuffer (doifemptyelse?) since one could think of similar commands that test for empty "objects".
>> Is there an option for testing blocks? (I actually use blocks quite frequently …)
>> I just realized they are probably handled very differently during the typesetting. Basically I would just need to test if during the first run any of \beginBLOCK … \endBLOCK was invoked (but if one gets a test for some content in-between that's even better).
>> As an alternative solution, is there a way to add content to buffers? Unfortunately, I can't use \getbuffer[first,second], but \startbuffer[first][add=yes] … \stopbuffer would be nice.
> just for fun I made this:
> 
> \starttext
> 
> \startbuffer[test]
>    test
> \stopbuffer
> 
> \startbuffer[oeps]
>    oeps
> \stopbuffer
> 
> \typebuffer[test] \getbuffer[test]
> 
> \startbuffer[test = * + test]
>    prepend
> \stopbuffer
> 
> \typebuffer[test] \getbuffer[test]
> 
> \startbuffer[test = test + *]
>    append
> \stopbuffer
> 
> \typebuffer[test] \getbuffer[test]
> 
> \startbuffer[test = * +++ test]
>    before
> \stopbuffer
> 
> \typebuffer[test] \getbuffer[test]
> 
> \startbuffer[test = test +++ *]
>    after
> \stopbuffer
> 
> \typebuffer[test] \getbuffer[test]
> 
> \startbuffer[test = * + oeps + test + oeps + * ]
>    DONE
> \stopbuffer
> 
> \typebuffer[test] \getbuffer[test]
> 
> \stoptext
> 
> which results in
> 
> test
> test
> prependtest
> prependtest
> prependtestappend
> prependtestappend
> before
> prependtestappend
> before
> prependtestappend
> before
> prependtestappend
> after
> before
> prependtestappend
> after
> DONEoepsbefore
> prependtestappend
> afteroepsDONE
> DONEoepsbefore
> prependtestappend
> afteroepsDONE
> 
> so basically one can combine buffers any way
> 
> +   : nothing in between
> ++  : space in between
> +++ : empty line in between
> 
> 
> -----------------------------------------------------------------
>                                          Hans Hagen | PRAGMA ADE
>              Ridderstraat 27 | 8061 GH Hasselt | The Netherlands
>       tel: 038 477 53 69 | www.pragma-ade.nl | www.pragma-pod.nl
> -----------------------------------------------------------------

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Re: How to check if buffer or block has content

[Hans Hagen via ntg-context]

On 8/2/2021 8:54 PM, Benjamin Buchmuller via ntg-context wrote:
> That's great, I wikified a Note for testing if a buffer exists or has content (using the \getbuffer[…] approach for the moment).
> 
> If I was asked, I'd opt for \doifelseemptybuffer (doifemptyelse?) since one could think of similar commands that test for empty "objects".
> 
> Is there an option for testing blocks? (I actually use blocks quite frequently …)
> 
> I just realized they are probably handled very differently during the typesetting. Basically I would just need to test if during the first run any of \beginBLOCK … \endBLOCK was invoked (but if one gets a test for some content in-between that's even better).
> 
> As an alternative solution, is there a way to add content to buffers? Unfortunately, I can't use \getbuffer[first,second], but \startbuffer[first][add=yes] … \stopbuffer would be nice.
just for fun I made this:

\starttext

\startbuffer[test]
     test
\stopbuffer

\startbuffer[oeps]
     oeps
\stopbuffer

\typebuffer[test] \getbuffer[test]

\startbuffer[test = * + test]
     prepend
\stopbuffer

\typebuffer[test] \getbuffer[test]

\startbuffer[test = test + *]
     append
\stopbuffer

\typebuffer[test] \getbuffer[test]

\startbuffer[test = * +++ test]
     before
\stopbuffer

\typebuffer[test] \getbuffer[test]

\startbuffer[test = test +++ *]
     after
\stopbuffer

\typebuffer[test] \getbuffer[test]

\startbuffer[test = * + oeps + test + oeps + * ]
     DONE
\stopbuffer

\typebuffer[test] \getbuffer[test]

\stoptext

which results in

test
test
prependtest
prependtest
prependtestappend
prependtestappend
before
prependtestappend
before
prependtestappend
before
prependtestappend
after
before
prependtestappend
after
DONEoepsbefore
prependtestappend
afteroepsDONE
DONEoepsbefore
prependtestappend
afteroepsDONE

so basically one can combine buffers any way

+   : nothing in between
++  : space in between
+++ : empty line in between


-----------------------------------------------------------------
                                           Hans Hagen | PRAGMA ADE
               Ridderstraat 27 | 8061 GH Hasselt | The Netherlands
        tel: 038 477 53 69 | www.pragma-ade.nl | www.pragma-pod.nl
-----------------------------------------------------------------
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Re: How to check if buffer or block has content

[Hans Hagen via ntg-context]

On 8/2/2021 8:54 PM, Benjamin Buchmuller via ntg-context wrote:
> That's great, I wikified a Note for testing if a buffer exists or has content (using the \getbuffer[…] approach for the moment).
> 
> If I was asked, I'd opt for \doifelseemptybuffer (doifemptyelse?) since one could think of similar commands that test for empty "objects".
> 
> Is there an option for testing blocks? (I actually use blocks quite frequently …)
> 
> I just realized they are probably handled very differently during the typesetting. Basically I would just need to test if during the first run any of \beginBLOCK … \endBLOCK was invoked (but if one gets a test for some content in-between that's even better)

indeed, multiple axis ... so then we need three arguments instead of one 
for the test

\defineblock[testa]
\defineblock[testb]

\starttext

\begintesta
     oeps
\endtesta

\doifelseblocksempty {testa}{}{} {YES} {NOP} % {name}{tag}{criterium}
\doifelseblocksempty {testb}{}{} {YES} {NOP} % {name}{tag}{criterium}

\stoptext

but you have to wikify it

Hans


-----------------------------------------------------------------
                                           Hans Hagen | PRAGMA ADE
               Ridderstraat 27 | 8061 GH Hasselt | The Netherlands
        tel: 038 477 53 69 | www.pragma-ade.nl | www.pragma-pod.nl
-----------------------------------------------------------------
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___________________________________________________________________________________

Re: How to check if buffer or block has content

[Benjamin Buchmuller via ntg-context]

That's great, I wikified a Note for testing if a buffer exists or has content (using the \getbuffer[…] approach for the moment). 

If I was asked, I'd opt for \doifelseemptybuffer (doifemptyelse?) since one could think of similar commands that test for empty "objects".

Is there an option for testing blocks? (I actually use blocks quite frequently …) 

I just realized they are probably handled very differently during the typesetting. Basically I would just need to test if during the first run any of \beginBLOCK … \endBLOCK was invoked (but if one gets a test for some content in-between that's even better).

As an alternative solution, is there a way to add content to buffers? Unfortunately, I can't use \getbuffer[first,second], but \startbuffer[first][add=yes] … \stopbuffer would be nice.

Thanks!


Benjamin

> On Aug 2, 2021, at 17:17, ntg-context-request@ntg.nl wrote:
> 
> \starttext
> 
> \startbuffer[test]
> test
> \stopbuffer
> 
> \doifelsebuffer{test} {YES} {NOP}
> 
> \permanent\protected\def\doifelsebuffercontent#1%
>  {\doifelse{\luaexpr{(string.strip(buffers.getcontent("#1")) ~= "" and "yes")}}{yes}}
> 
> \startbuffer[test]
> \stopbuffer
> 
> \doifelsebuffercontent{test} {YES} {NOP}
> 
> \startbuffer[test]
> 
> \stopbuffer
> 
> \doifelsebuffercontent{test} {YES} {NOP}
> 
> \stoptext

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