MetaFun: how to check the number of arguments

[Jeong Dal <haksan@me.com>]

Dear all,

In the following sample, it draws squares with label which is given.

I’d like to know how to check the number of elements in the second argument?
If it is 0, then I just draw grids only.

Thank you for reading.
Best regards,

Dalyoung

********
\startbuffer[defs]
def drawGridF (expr nb) (text s) = 
	p := unitsquare scaled wu;
	n:= 0;
	for m = s:
		i:= n mod nb;
		j:= n div nb;
		pic := image (draw p; label(textext(m), center p); );
		draw pic shifted (i*wu, j*wu);
		n:= n+ 1;
	endfor;
enddef;
\stopbuffer

\startbuffer[3x3b]
wu := \MPvar{width};
drawGridF (3)  (1,2,3,0,1, 1,4,5,8);
\stopbuffer

\starttext
\setupMPvariables[width=30pt]
\processMPbuffer[defs,3x3b]
\stoptext

> 2019. 1. 14. 오후 8:00, ntg-context-request@ntg.nl 작성:
> 
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> Today's Topics:
> 
>   1. Re: Manipulating the left blank page when chapter starts on
>      the right page (Wolfgang Schuster)
>   2. Re: Footnotes in float combinations missing in output
>      (Wolfgang Schuster)
>   3. Re: Manipulating the left blank page when chapter starts on
>      the right page (Jan U. Hasecke)
> 
> 
> ----------------------------------------------------------------------
> 
> Message: 1
> Date: Sun, 13 Jan 2019 16:56:40 +0100
> From: Wolfgang Schuster <wolfgang.schuster.lists@gmail.com>
> To: mailing list for ConTeXt users <ntg-context@ntg.nl>, "Jan U.
> 	Hasecke" <juh+ntg-context@mailbox.org>
> Subject: Re: [NTG-context] Manipulating the left blank page when
> 	chapter starts on the right page
> Message-ID: <cad2dcf9-ce2c-203a-88c2-41315bd5f825@gmail.com>
> Content-Type: text/plain; charset=utf-8; format=flowed
> 
> Jan U. Hasecke schrieb am 12.01.19 um 22:08:
>> Hi Aditya,
>> 
>> Am 12.01.19 um 20:11 schrieb Aditya Mahajan:
>>> On Sat, 12 Jan 2019, Jan U. Hasecke wrote:
>>> 
>>>> Hi all,
>>>> 
>>>> in my document \startchapter and \starttitle starts a new chapter on the
>>>> right (odd) page. So sometimes, there is a blank even page just before a
>>>> new chapter.
>>>> 
>>>> I would like to manipulate this blank even page.
>>>> 
>>>> There are several things I would like to do, eg. having no headers and
>>>> footers, setting the background color to a named color, placing an image
>>>> or some graphics on the page.
>>>> 
>>>> Is there a way to define such a page, name it and call it in
>>>> \startchapter so that it is placed on the left side.
>>> See https://tex.stackexchange.com/q/457428/323
>> Thanks a lot, but I wasn't looking for a way to just delete page numbers
>> but to style the empty page in arbitrary ways.
>> 
>> Maybe it is better to do this manually.
>> 
>> I would let chapter open on even pages too and just insert a styled page
>> by hand.
> 
> Here is a example which shows how you can change the background color
> of a empty page before the chapter title.
> 
> \setuppagenumbering
>   [alternative=doublesided]
> 
> \startsetups [chapter:before]
>   \doifoddpageelse
>     {}
>     {\pushbackground[page]
>      \setupbackgrounds[page][background=color,backgroundcolor=black]
>      \page[empty,right]
>      \popbackground}
> \stopsetups
> 
> \setuphead
>   [chapter]
>   [page=yes,
>    before=\directsetup{chapter:before}]
> 
> \starttext
> 
> \startchapter[title={Knuth}]
> \dorecurse{10}{\samplefile{knuth}}
> \stopchapter
> 
> \startchapter[title={Zapf}]
> \dorecurse{10}{\samplefile{zapf}}
> \stopchapter
> 
> \startchapter[title={Ward}]
> \dorecurse{10}{\samplefile{ward}}
> \stopchapter
> 
> \stoptext
> 
> Wolfgang
> 
> 
> 
> ------------------------------
> 
> Message: 2
> Date: Sun, 13 Jan 2019 21:06:42 +0100
> From: Wolfgang Schuster <wolfgang.schuster.lists@gmail.com>
> To: mailing list for ConTeXt users <ntg-context@ntg.nl>, Lars
> 	<axteffekt@gmail.com>
> Subject: Re: [NTG-context] Footnotes in float combinations missing in
> 	output
> Message-ID: <e14cd1c5-400e-14bf-d8bf-a47ef28b6550@gmail.com>
> Content-Type: text/plain; charset=utf-8; format=flowed
> 
> Lars schrieb am 09.01.19 um 23:01:
>> Hi there, hi Hans,
>> 
>> I just want to let you know that footnotes insterted in 
>> float-combinations don't get rendered properly, i. e. only the last 
>> footnote is placed in the output. MWE:
>> 
>> \starttext
>>   \startplacefigure[title={OuterCap\footnote{Outer footnote}}]
>> 
>>     \startfloatcombination[nx=3]
>> \placefigure{Fnote1\footnote{Hello}}{\externalfigure[cow][width={.2\textwidth}]}
>> \placefigure{Fnote2\footnote{small}}{\externalfigure[cow][width={.2\textwidth}]}
>> \placefigure{Fnote3\footnote{world}}{\externalfigure[cow][width={.2\textwidth}]}
>>     \stopfloatcombination
>> 
>>   \stopplacefigure
>> \stoptext
> 
> Not very nice but the following works. You would have less problems with 
> local footnotes which are placed in the float block.
> 
> \starttext
> 
> \startpostponingnotes
>   \startplacefigure[title={...}]
>     ...
>   \stopplacefigure
> \stoppostponingnotes
> 
> \stoptext
> 
> Wolfgang
> 
> 
> ------------------------------
> 
> Message: 3
> Date: Mon, 14 Jan 2019 08:39:45 +0100
> From: "Jan U. Hasecke" <juh+ntg-context@mailbox.org>
> To: Wolfgang Schuster <wolfgang.schuster.lists@gmail.com>, mailing
> 	list for ConTeXt users <ntg-context@ntg.nl>
> Subject: Re: [NTG-context] Manipulating the left blank page when
> 	chapter starts on the right page
> Message-ID: <d88401b5-1ada-6f97-ee9b-f0e8fe83cb45@mailbox.org>
> Content-Type: text/plain; charset=utf-8
> 
> 
> Am 13.01.19 um 16:56 schrieb Wolfgang Schuster:
> 
>> Here is a example which shows how you can change the background color
>> of a empty page before the chapter title.
>> 
>> \setuppagenumbering
>>   [alternative=doublesided]
>> 
>> \startsetups [chapter:before]
>>   \doifoddpageelse
>>     {}
>>     {\pushbackground[page]
>>      \setupbackgrounds[page][background=color,backgroundcolor=black]
>>      \page[empty,right]
>>      \popbackground}
>> \stopsetups
>> 
>> \setuphead
>>   [chapter]
>>   [page=yes,
>>    before=\directsetup{chapter:before}]
>> 
>> \starttext
>> 
>> \startchapter[title={Knuth}]
>> \dorecurse{10}{\samplefile{knuth}}
>> \stopchapter
>> 
>> \startchapter[title={Zapf}]
>> \dorecurse{10}{\samplefile{zapf}}
>> \stopchapter
>> 
>> \startchapter[title={Ward}]
>> \dorecurse{10}{\samplefile{ward}}
>> \stopchapter
>> 
>> \stoptext
> 
> Thanks a lot Wolfgang!
> 
> This was just the thing I was looking for. These setups seems to be the
> golden bullet in ConTeXt but I often have difficulties to understand the
> mechanism.
> 
> I'll try to wikify this later this week.
> 
> The push-pop-background pair is mentionend in x-setups-overview together
> with some other push-pop-pairs or push single commands. Are they
> documented somewhere?
> 
> juh
> 
> 
> 
> ------------------------------
> 
> Subject: Digest Footer
> 
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> 
> End of ntg-context Digest, Vol 175, Issue 27
> ********************************************

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