How to specify [ and ] in a macro invocation in ConTeXt

Question

If have the following ConTeXt macros:

\def\tableHeader#1 {%
    \start
    \setupTABLE[frame=on,offset=1mm]
    \setupTABLE[c][1][width=0.25\textwidth]
    \setupTABLE[c][2][width=0.75\textwidth]
    \bTABLE
        \bTR
            \bTH[nc=2] #1 \eTH
        \eTR
}

\def\tableFooter {%
    \eTABLE
    \stop
}

\def\tableItem#1#2 {%
    \bTR
        \bTD #1 \eTD
        \bTD #2 \eTD
    \eTR
}

How do I call this macro with '[\w ]+' as second parameter? That is:

\tableHeader{Example}
\tableItem{Regex}{[\w ]+}
\tableFooter

Answer 1

Here you want to ensure that [ isn't seen as the start of an argument by \bTD. To do that, the easiest way is to insert a \relax. As you are making this part of a macro, I'd do that in the definition not each time you pass an argument

\def\tableItem#1#2 {%
    \bTR
        \bTD\relax #1 \eTD
        \bTD\relax #2 \eTD
    \eTR
}
\starttext
\bTABLE
\tableItem{Regex}{[\string\w\space]+}
\eTABLE
\stoptext

I suspect you want something like

\tableItem{Regex}{\type{[\w ]+}}

which would avoid the need for the \relax in this case as \type will also stop the scanning for a [, but it's likely best to keep the \relax anyway.

---

Working example using edited question: notice that \w has to be made into a string one way or another

\def\tableHeader#1 {%
    \start
    \setupTABLE[frame=on,offset=1mm]
    \setupTABLE[c][1][width=0.25\textwidth]
    \setupTABLE[c][2][width=0.75\textwidth]
    \bTABLE
        \bTR
            \bTH[nc=2] #1 \eTH
        \eTR
}

\def\tableFooter {%
    \eTABLE
    \stop
}

\def\tableItem#1#2 {%
    \bTR
        \bTD\relax #1 \eTD
        \bTD\relax #2 \eTD
    \eTR
}
\starttext
\tableHeader{Example}
\tableItem{Regex}{[\string\w\space]+}
\tableFooter
\stoptext

Answer 2

If you really to simply type [\w ]+, you can change the catcode table so that \ is not a special character.

One way to do this is to use the \tbacatcodes catcode table (defined in catc-ctx.mkiv), that only sets the normal catcodes of { and }; everything else, including \ has catcode other. Note that this means that you cannot use unmatched { and } inside the argument of \tableItem.

While I was at it, I also made a few stylistic changes to your code:

1. Use setups to setup table style
2. Use \define instead of \def. Keep in mind that space is significant in TeX, so \def\tableItem#1#2 { is different from \def\tableItem#1#2{.

The complete code is below

\startsetups regex-table
  \setupTABLE[frame=on,offset=1mm]
  \setupTABLE[c][1][width=0.25\textwidth]
  \setupTABLE[c][2][width=0.75\textwidth]
\stopsetups

\define[1]\tableHeader
  {\bTABLE[setups=regex-table]
    \bTR 
      \bTH[nc=2] #1 \eTH 
    \eTR}

\define\tableFooter{\eTABLE}

\define\tableItem
   {\pushcatcodetable
    \setcatcodetable\tpacatcodes
    \doTableItem}

\define[2]\doTableItem
   {\bTR
        \bTD\relax #1 \eTD
        \bTD\relax #2 \eTD
    \eTR
    \popcatcodetable}

\starttext
\tableHeader{Example}
\tableItem{Regex}{[\w ]+}
\tableFooter
\stoptext