\do(single|double|etc)empty behaviour

\do(single|double|etc)empty behaviour

[Marco Pessotto]

Hello there.

I was writing a small macro to emulate a custom \part command, and I
broke my head against \dosingleempty (but finally I won). 

Why this example is working:

%%%%%%%%% start %%%%%%%%%%%%%%%%%
\definelist[talpart]
\define\talpart{\page[right]%
  \blank[2*big]%
  \startalignment[center]%
    \dosingleempty\doTalPart}
\def\doTalPart[#1]#2{%
    \iffirstargument
    debug: I have the optional arg
    \bfc#1\blank[2*big]
    \writetolist[talpart]{}{{#1. }#2}
    \else
    debug: I don't have any arg
    \blank[2*big]
    \writetolist[talpart]{}{#2}
    \fi
    \bfd#2
    \stopalignment
    \blank[2*big]
}

\starttext
\placelist[talpart]
\talpart[optional]{With optional argument}
\input knuth
\talpart{No argument}
\input ward
\stoptext
%%%%%%%%%%% stop %%%%%%%%%%%%%%%%

While this, the original one, is definitively not working?

%%%%%%%%% start %%%%%%%%%%%%%%%%%
\definelist[talpart]
\define\talpart{\dosingleempty\doTalPart}
\def\doTalPart[#1]#2{%
  \page[right]
  \startalignment[center]
    \blank[force,2*big]
    \iffirstargument
    debug: I have the optional arg
      \noindent{\bfc#1}\blank[2*big]
      \writetolist[talpart]{}{{#1. }#2}
    \else
    debug: I don't have any arg
      \blank[2*big]
      \writetolist[talpart]{}{#2}
    \fi
      {\noindent \bfd#2}
    \stopalignment
    \page[left]
}
\starttext
\placelist[talpart]
\talpart[optional]{With optional argument}
\input knuth
\talpart{No argument}
\input ward
\stoptext
%%%%%%%%%%% stop %%%%%%%%%%%%%%%%

It's unclear to me how the arguments are passed between macros.
Probably it's just a matter of knowledge of TeX macro programming (which
obviously I don't have).

My source of inspiration was:
http://wiki.contextgarden.net/Commands_with_optional_arguments

Bests

-- 
Marco

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___________________________________________________________________________________

Re: \do(single|double|etc)empty behaviour

[Wolfgang Schuster]

Am 15.12.2010 um 19:40 schrieb Marco Pessotto:

> 
> Hello there.
> 
> I was writing a small macro to emulate a custom \part command, and I
> broke my head against \dosingleempty (but finally I won). 
> 
> […]
> 
> It's unclear to me how the arguments are passed between macros.
> Probably it's just a matter of knowledge of TeX macro programming (which
> obviously I don't have).

Your test with \iffirstargument fails because you perform it after \startalignment
which has itself a argument which sets \iffirstargument to true, a better way to
check for content of the optional argument is \doifsomethingelse.

\def\talpart
  {\dosingleempty\dotalpart}

\def\dotalpart[#1]#2%
  {\page[right]
   \blank[force,2*big]
   \startalignment[center]
   \doifsomethingelse{#1}
     {{\bfc#1}\writetolist[talpart]{}{#1. #2}}
     {\writetolist[talpart]{}{#2}}%
   \blank[2*big]
   {\bfd#2}
   \stopalignment
   \page[left]}

Wolfgang

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maillist : ntg-context@ntg.nl / http://www.ntg.nl/mailman/listinfo/ntg-context
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___________________________________________________________________________________

Re: \do(single|double|etc)empty behaviour

[Marco Pessotto]

Wolfgang Schuster <schuster.wolfgang@googlemail.com> writes:

> Am 15.12.2010 um 19:40 schrieb Marco Pessotto:
>
>> 
>> Hello there.
>> 
>> I was writing a small macro to emulate a custom \part command, and I
>> broke my head against \dosingleempty (but finally I won). 
>> 
>> […]
>> 
>> It's unclear to me how the arguments are passed between macros.
>> Probably it's just a matter of knowledge of TeX macro programming
>> (which obviously I don't have).
>
> Your test with \iffirstargument fails because you perform it after
> \startalignment which has itself a argument which sets
> \iffirstargument to true, a better way to check for content of the
> optional argument is \doifsomethingelse.
>
> \def\talpart
>   {\dosingleempty\dotalpart}
>
> \def\dotalpart[#1]#2%
>   {\page[right]
>    \blank[force,2*big]
>    \startalignment[center]
>    \doifsomethingelse{#1}
>      {{\bfc#1}\writetolist[talpart]{}{#1. #2}}
>      {\writetolist[talpart]{}{#2}}%
>    \blank[2*big]
>    {\bfd#2}
>    \stopalignment
>    \page[left]}
>
> Wolfgang
>

Thanks a lot for your explanation. I've added a "pitfalls" section to
http://wiki.contextgarden.net/Commands_with_optional_arguments#Pitfalls
(well, it was a pitfall at least for me)

-- 
Marco

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maillist : ntg-context@ntg.nl / http://www.ntg.nl/mailman/listinfo/ntg-context
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___________________________________________________________________________________