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In LaTeX you define a new command < [[Inside ConTeXt]] | [[Commands with an optional argument with "newcommand":KeyVal arguments]] >
ConTeXtFor a command with two optional arguments, we use:<texcode>\def\MyCommand{\dodoubleempty\doMyCommand}</texcode>
There We then create the "private" macro (<tt>\doMacroName</tt> is perhaps a way to do the same. Otherwisetraditional ConTeXt name for these), with all the key value method is preferred, see [[Commands with KeyVal arguments]]defined as nonoptional. Default values for the arguments need to be handled somewhat more explicitly than with LaTeX; macros such as {{cmd|ifsecondargument}} are used to determine whether the given argument was specified, as follows:
----<texcode> \def\doMyCommand[#1][#2]{#1Hello \ifsecondargument #2% \else World% \fi !}</texcode>
<i>The following Note that this makes both arguments optional -- something that is my understanding of how much more difficult to do this. It's currently untested; someone please test this and integrate it with the above. --in LaTeX ([[Userhttp:Brooks|Brooks]]</i> In ConTeXt, the optional argument processing is handled as a two-step process/www.tex.ac. First, we write the command for the end-user as a wrapper command, which calls <tt>\dodoubleempty<uk/tt> (from <tt>systcgi-gen.tex<bin/tt>texfaq2html?label=twooptarg but can be done]) to handle the arguments properly -- including the optional ones -- and then calls a "private" command . This also means that contains we should reverse the internals order of arguments, since if the macro. Note that this function call does not explicitly refer to user specifies only one argument it will be treated as the arguments at allfirst argument.
\def(Also, note that <tt>\MyCommand{\dodoubleempty</tt> without the second argument ends up gobbling the following spaces, so we need to explicitly include one with "<tt>\doMyCommand}</tt>".)
We then create the "private" macro (<tttexcode>\doMacroName</tt> is the traditional ConTeXt name for these), with all the arguments defined as nonoptional. Default values for the arguments need to be handled somewhat more explicitly than with LaTeX; macros such as <tt>MyCommand[\bf]\ %\MyCommand[\ifsecondargumentsc][Hans]</tttexcode> are used to determine whether the given argument was specified, as follows:
<context>\def\MyCommand{\dodoubleempty\doMyCommand}\def\doMyCommand[#1][#2]{#1Hello
Note that this makes both arguments optional -- something that is much more difficult to do in LaTeX ([http://www.tex.ac.uk/cgi-bin/texfaq2html?label=twooptarg but can be done]). This also means that we should reverse the order of arguments, since if the user specifies only one argument it will be treated as the first argument.
If you don't want any optional argumentsOn a final note, but still want your arguments enclosed for comparative purposes: in <tt>[]</tt> LaTeX, a new command with an optional argument is defined with appropriate handling for spaces (or line breaks) between the square brackets, use <ttcode>\dodoubleargumentsnewcommand</ttcode> instead of . <tttexcode>\newcommand{\dodoubleemptyMyCommand}[2][World]{{#2Hello #1!}}\MyCommand{\bfseries}\MyCommand[Hans]{\scshape}</tttexcode>. 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.
----Reference: http://archive.contextgarden.net/message/20101215.225603.cc903e62.en.html
Also, does someone know how to define \mycommand[.1.[Category:Programming and Databases]][[.2.Category:Tools]]{.3.}? E.g., with curly braces around a non-optional third argument? I think this just involves adding a second, non-delimited argument to <tt>\doMyCommand</tt>, but I'm not sure. Also, can someone test to see if <tt>\dosingleempty</tt> and <tt>\dodoubleargument</tt> can be chained, to get two square-bracketed arguments only one of which is optional?
Commands with optional arguments (view source)
Revision as of 17:04, 8 June 2020
, 17:04, 8 June 2020no edit summary
In ConTeXt, the optional argument processing is handled as a two-step process. \newcommandFirst, we write the command for the end-user as a wrapper command, which calls {\MyCommand{cmd|dosingleempty}}[2][World], {{#2Hello #1!cmd|dodoubleempty}} \MyCommand, {{cmd|dotripleempty}}, ... (from {{\bfseriessrc|syst-aux.mkiv} \MyCommand[Hans]} or {{\scshapesrc|syst-gen.mkii}}) to handle the arguments properly -- including the optional ones -- and then calls a "private" command that contains the internals of the macro. Note that this function call does not explicitly refer to the arguments at all.
\ifsecondargument
#2%
\fi
!}
\MyCommand[\bf]\ %
\MyCommand[\sc][Hans]
</context>
If you ''don't'' want any optional arguments, but still want your arguments enclosed in <tt>[]</tt> with appropriate handling for spaces (or line breaks) between the square brackets, use {{cmd|dodoubleargument}} instead of {{cmd|dodoubleempty}}. 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 {{src|syst-aux.mkiv}} for the exact names.
=== Examples ===
To define <code>\mycommand[#1]{#2}</code> with one optional argument and one mandatory argument, do the following
<context source="yes">
\def\mynewcommand{\dosingleempty\doMyNewCommand}
\def\doMyNewCommand[#1]#2{%
\iffirstargument
There is an optional parameter: {\bf #1}\par%
\else
No optional parameter\par%
\fi
This is the mandatory text: {\em #2}%
}
\starttext
\mynewcommand[opt]{Hello People}
\blank
\mynewcommand{Hello People}
\stoptext
</context>
To define <code>\mycommand[#1][#2]{#3}</code> with two optional arguments and one mandatory argument, do
<texcode>
\def\mycommand{\dodoubleempty\doMycommand}
\def\doMycommand[#1][#2]#3{whatever}
</texcode>
=== Pitfalls ===
Please keep in mind that <code>\iffirstargument</code> will always return true if you put before it a command which itself has an argument. See the following example:
<context source="yes" text="produces">
\def\mynewcommand{\dosingleempty\doMyNewCommand}
\def\doMyNewCommand[#1]#2{%
\startalignment[center]
\iffirstargument
There is an optional parameter: {\bf #1}\par%
\else
No optional parameter\par%
\fi
This is the mandatory text: {\em #2}%
\stopalignment
}
\starttext
\mynewcommand[opt]{Hello People}
\blank
\mynewcommand{Hello People}
\stoptext
</context>
Use <code>\doifsomethingelse</code> instead:
<context source="yes" text="this time is correct:">
\def\mynewcommand{\dosingleempty\doMyNewCommand}
\def\doMyNewCommand[#1]#2{%
\startalignment[center]%
\doifsomethingelse{#1}
{There is an optional parameter: {\bf #1}\par}
{No optional parameter\par}
This is the mandatory text: {\em #2}
\stopalignment%
}
\starttext
\mynewcommand[opt]{Hello People}
\blank
\mynewcommand{Hello People}
\stoptext
</context>
