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<small><pre> \newcommand{\MyCommand}[2][World]{{#2Hello #1!}} \MyCommand{\bfseries} \MyCommand[Hans]{\scshape}</pre></small>
Commands with optional arguments (view source)
Revision as of 18:27, 4 August 2004
, 18:27, 4 August 2004Added \dodoubleempty, etc.; this needs testing and editing.
In LaTeX you define a new command with an optional argument with "newcommand":
ConTeXt:
There is perhaps a way to do the same. Otherwise, the key value method is preferred, see [[Define Commands]].
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<i>The following is my understanding of how to do this. It's currently untested; someone please test this and integrate it with the above. --[[User:Brooks|Brooks]]</i>
In ConTeXt, the optional argument processing is handled as a two-step process. First, the internals of the desired command are put in a "private" macro, without optional arguments:
\def\doMyCommand[#1][#2]{{#2Hello #1!}}
Then, this is wrapped in the main command, which calls <tt>\dodoubleempty</tt> (from <tt>syst-gen.tex</tt>) to handle the arguments -- including the optional ones. Note that this function call does not explicitly refer to the arguments at all.
\def\MyCommand{\dodoubleempty \doMyCommand}
This does not, however, provide a way of directly supplying default values; instead, any values not specified by the user are given as empty. Macros such as <tt>\iffirstargument</tt> are used to determine whether the given argument was specified. Thus, we could handle those in <tt>\doMyCommand</tt>:
\def\doMyCommand[#1][#2]{#2Hello
\iffirstargument
#1%
\else
World%
\fi
!}
Note that this makes both arguments optional -- something that is much more difficult to do in LaTeX.
If you don't want any optional arguments, but want your arguments enclosed in <tt>[]</tt> with appropriate handling for spaces (or line breaks) between the square brackets, use <tt>\dodoublearguments</tt> instead of <tt>\dodoubleempty</tt>. There are of course versions for other numbers of arguments, found by replacing <tt>double</tt> with <tt>single</tt> through <tt>seventuple</tt>; see <tt>syst-gen.tex</tt> for the exact names.
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Also, does someone know how to define \mycommand[.1.][.2.]{.3.}? E.g., with curly braces around a non-optional third argument?
