Command/dodoublegroupempty

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\dodoublegroupempty

Syntax

\dodoublegroupempty\commmand

Description

\dodoublegroupempty is used to write commands that can take zero, one, or two arguments in braces: if the user specifies less than two arguments, it adds empty arguments at the end to make up the missing numbers.

So, \dodoublegroupempty\command leads to:

\command{#1}{#2} % or
\command{#1}{}   % or
\command{}{}     %    ,

depending on the generosity of the user. Afterwards one can use the \iffirstargument, \ifsecondargument, ... tests to determine how many arguments were actually passed.

There are variants of this command that will supply anywhere up to seven optional arguments:

  • \dosinglegroupempty
  • \dodoublegroupempty
  • \dotriplegroupempty
  • \doquadruplegroupempty
  • \doquintuplegroupempty

Example

This is the standard pattern for writing a command that takes an optional number of arguments in braces:

% This command accepts two optional arguments
\def\writename%
   {\dodoublegroupempty
    \dowritename}

% This command looks at how many non-empty arguments 
% are supplied, and acts accordingly
\def\dowritename#1#2%
   {\ifsecondargument
       Ms. #2 (first name #1)%
    \else\iffirstargument
       Ms. #1%
    \else
       No name supplied.%
    \fi\fi}

\writename{Snow}{White} \par
\writename{White} \par
\writename

See also

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