Changes

In LaTeX you define a new command with an optional argument with "newcommand": <texcode>\newcommand{\MyCommand}[2][World]{{#2Hello #1!}}\MyCommand{\bfseries}\MyCommand[Hans]{\scshape}</texcode> <context>{\bf Hello World!}{\sc Hello Hans!}</context> In ConTeXt, 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 <{{cmd|dosingleempty}}, {{cmd>|dodoubleempty</}}, {{cmd> |dotripleempty}}, ... (from [http://source.contextgarden.net/tex/context/base/{{src|syst-genaux.tex mkiv}} or {{src|syst-gen.tex]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.

We then create the "private" macro (<tt>\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:

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</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 [http://source.contextgarden.net/tex/context/base/syst-gen.mkii {{src|syst-genaux.tex] mkiv}} for the exact names.

To define <ttcode>\mycommand[.#1.][.2.]{.3.}</tt>, i.e., with curly braces around a non-optional third argument, you just define <texcode>\def\mycommand{\dodoubleempty\doMycommand}\def\doMycommand[#1][#2]#3{whatever}</texcode>    To define <code>\mycommand[with one optional]{text}</code>argument and one mandatory argument, do the following <texcodecontext source="yes"> 

There is an optional parameter: {\bf #1}\par%

No optional parameter\par%

This is the mandatory text: {\em #2}%

</texcodecontext>

To define <code>\def\mynewcommand{\dosingleempty\doMyNewCommand}\def\doMyNewCommandmycommand[#1][#2]{% \iffirstargument There is an optional parameter: {\bf #13}\par \else No </code> with two optional parameter\par \fi This is the arguments and one mandatory text: {\em #2}}argument, do

<texcode>\starttextdef\mynewcommand[opt]mycommand{Hello People\dodoubleempty\doMycommand}\blankdef\mynewcommanddoMycommand[#1][#2]#3{Hello Peoplewhatever}\stoptext</contexttexcode>

Please keep ==== Passing preceding command's argument ==== 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:

There is an optional parameter: {\bf #1}\par%

No optional parameter\par%

This is the mandatory text: {\em #2}%

<context source="yes" text="This time this time is correct:">

\startalignment[center]%

\stopalignment%

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