Why does ConTeXt use \NC..\NR instead of &..\cr?

Question

When Knuth came up with the catcode table, he dedicated the character & to catcode 4, the alignment tab. It happens rarely that people change these default catcodes and I guess most users have accustomed themselves to typesetting tabulated material by denoting the alignment points with &. Plain TeX users type

\halign{\hfil#\hfil&\hfil#\hfil\cr
  A & B \cr
  C & D \cr
}
\bye

and LaTeX users enjoy the simplified `tabular interface

\documentclass{article}
\begin{document}
\begin{tabular}{cc}
  A & B \\
  C & D \\
\end{tabular}
\end{document}

but in ConTeXt MkIV one has

\starttext
\starttabulate[|c|c|]
  \NC A \NC B \NR
  \NC C \NC D \NR
\stoptabulate
\stoptext

I wonder why, because \NC..\NR are more tokens to type than &..\cr, especially with that redundant \NC in the beginning of the line and it makes, in my opinion, the source less readable. I also noticed that & has catcode 12 (other) in a ConTeXt document.

But, everything is there for a reason, so the question is: Why does ConTeXt choose to use \NC..\NR instead of &..\cr and why is the catcode of & 12?

Answer 1

I don't know what was the original reason why Hans Hagen used \NC instead of &. In the original table macros, there was also \VL for vertical rule \HC for "hook" column, etc. So, perhaps it was introduced to have a consistent syntax.

But, I find it most useful because it allow for a very clean separation between content and style. And, I don't mind typing a few extra keys, because after a while it just becomes muscle memory: Shift \ n c <release Shift>. Let me illustrate what I mean by separation of content and style by a few examples:

1. Spanning rows and column. How do you create the following table?

   

   In LaTeX, you would create a multi-column and then a multi-row inside. Contrast that with the ConTeXt code:

   \starttext
     \startTABLE
       \NC[nx=2,ny=2] A big cell \NC A \NC B \NC \NR
                                 \NC C \NC D \NC \NR
       \NC E     \NC   F         \NC G \NC H \NC \NR
     \stopTABLE
   \stoptext
   

   Because \NC is a macro (and not a primitive), it is straight forward for it to take an optional argument.

2. Separation of content and presentation. Suppose I want a table with rules before and after the first row, a rule after the last row, and the content of the first row in bold (this is a common table format).

   

   In LaTeX, you'll need to manually add the \toprule and \midrule and add \textbf around each element of the first row. In ConTeXt, you can do the following:

   \startsetups standard
     \setupTABLE[frame=off]
     \setupTABLE[row][first][style=bold]
     \setupTABLE[row][first][topframe=on, rulethickness=2pt]
     \setupTABLE[row][2][topframe=on, rulethickness=1pt]
     \setupTABLE[row][last][bottomframe=on, rulethickness=1.5pt]
   \stopsetups
   
   \starttext
     \startTABLE[setups={standard}]
       \NC 1st header \NC 2nd header \NC 3rd header \NC \NR
       \NC value      \NC value      \NC value      \NC \NR
       \NC value      \NC value      \NC value      \NC \NR
       \NC value      \NC value      \NC value      \NC \NR
       \NC value      \NC value      \NC value      \NC \NR
     \stopTABLE
   \stoptext
   

   Now suppose, your boss says that he wants fancy tables like Word.

   

   Well, you just need a new setups, and you have go it:

   \definecolor[blue][b=0.8]
   \startsetups uglytable
     \setupTABLE[frame=off, framecolor=blue]
     \setupTABLE[row][first][style=bold, color=white, background=color, backgroundcolor=blue]
     \setupTABLE[column][first][leftframe=on]
     \setupTABLE[column][last][rightframe=on]
     \setupTABLE[row][last][bottomframe=on]
   \stopsetups
   

   Again, behind the scenes, this mechanism relies on the fact that \NC is a macro and not a primitive.

Sure, it is possible to do so without introducing any new macros: tikz tables does something similar and it keeps & as the column separator. But, IIRC, inside tikz matrix & is an active character which then maps to a macro; this brings all the usual trouble with active characters. In ConTeXt, one tends to avoid active characters as far as possible.