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< [[Inside ConTeXt]]| [[Commands with KeyVal arguments]] >

In LaTeX you define ConTeXt, the optional argument processing is handled as a two-step process. First, we write the command for the end-user as a new wrapper command with an , which calls {{cmd|dosingleempty}}, {{cmd|dodoubleempty}}, {{cmd|dotripleempty}}, ... (from {{src|syst-aux.mkiv}} or {{src|syst-gen.mkii}}) to handle the arguments properly -- including the optional argument with ones -- and then calls a "newcommandprivate":command that contains the internals of the macro. Note that this function call does not explicitly refer to the arguments at all.

\newcommand{\MyCommand}[2][World]{{#2Hello #1!}}def\MyCommand{\bfseries}\MyCommand[Hans]{dodoubleempty\scshapedoMyCommand}

In ConTeXt 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:

<i>The following Note that this makes both arguments optional -- something that is my understanding of how much more difficult to do thisin LaTeX ([http://www.tex.ac.uk/cgi-bin/texfaq2html?label=twooptarg but can be done]). It's currently untested; someone please test this and integrate This also means that we should reverse the order of arguments, since if the user specifies only one argument it with will be treated as the abovefirst argument. --[[User:Brooks|Brooks]]</i>

In ConTeXt(Also, the optional argument processing is handled as a two-step process. First, we write the command for the end-user as a wrapper command, which calls note that <cmdtt>dodoubleempty\MyCommand</cmdtt> (from without the second argument ends up gobbling the following spaces, so we need to explicitly include one with "<tt>syst-gen.tex\ </tt>) 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.)

\defMyCommand[\bf]\ %\MyCommand{\dodoubleempty[\doMyCommand}sc][Hans]

We then create the "private" macro (<ttcontext>\def\MyCommand{\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 <cmd>ifsecondargument</cmd> are used to determine whether the given argument was specified, as follows: <texcode>dodoubleempty\doMyCommand} \def\doMyCommand[#1][#2]{#1Hello

\MyCommand[\bf]\ %\MyCommand[\sc][Hans]</texcodecontext> 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 ===

Note that this makes both arguments To define <code>\mycommand[#1]{#2}</code> with one optional -- something that is much more difficult to argument and one mandatory argument, do in LaTeX (the following<context source="yes">\def\mynewcommand{\dosingleempty\doMyNewCommand}\def\doMyNewCommand[http#1]#2{% \iffirstargument There is an optional parameter://www.tex.ac.uk/cgi-bin/texfaq2html?label=twooptarg but can be done]). {\bf #1}\par% \else No optional parameter\par% \fi This also means that we should reverse is the order of arguments, since if the user specifies only one argument it will be treated as the first argument.mandatory text: {\em #2}%}

If you don't want any optional arguments, but still want your arguments enclosed in <tt>\starttext\mynewcommand[opt]{Hello People}\blank\mynewcommand{Hello People}\stoptext</tt> with appropriate handling for spaces (or line breaks) between the square brackets, use <cmd>dodoublearguments</cmd> instead of <cmd>dodoubleempty</cmd>. 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</ttcontext> for the exact names.

To define <ttcode>\mycommand[.#1.][.#2.]{.#3.}</ttcode>, i.e., with curly braces around a non-two optional third arguments and one mandatory argument, you just definedo

----=== 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>  On a final note, for comparative purposes: in LaTeX, a new command with an optional argument is defined with <code>\newcommand</code>. <texcode>\newcommand{\MyCommand}[2][World]{{#2Hello #1!}}\MyCommand{\bfseries}\MyCommand[Hans]{\scshape}</texcode> Reference: http://archive.contextgarden.net/message/20101215.225603.cc903e62.en.html

<i>Can someone test to see if <cmd>dosingleempty</cmd> [[Category:Programming and <cmd>dodoubleargument</cmd> can be chained, to get two square-bracketed arguments only one of which is optional?</i>Databases]][[Category:Tools]]