Re: Active character sequences

[Hans Hagen <pragma@wxs.nl>]

At 10:18 PM 11/24/00 +0100, Giuseppe Bilotta wrote:
>Hello, these are a few things I would like to obtain with ConTeXt now:
>
>1) I would like to have << and >> as synonyms for |<| and |>|;

This is a bad idea, since < [ ( are used for special purposes. Making <
active an active character is not a problem, but it may clash with other
functionality.  

>2) I would like to be able to define in and easy way similar commands, to
>give similar meanings to [[ and ]] (giving hollow opening and closing
>brackets, which I have already assigned to appropriate cs's);

That would brake all [parameters] since from then on "[ the active char"
would be different from "[ the other char' (in tex characters can have 16
different states!). Partial hacks are possible but never 100% safe. 

If your font would have a << as a ligature, it would be ok. 

>3) At the same time, I would like to use [ ... ] pairs as described in the
>cont-new.tex module (\defineshortcuts, which only works with < ... > pairs);

eh, core-new.tex i suppose, unless you have an old version

>is there a way to implement 2) without conflicting with 3)? Or to implement
>1) without conflicting with \defineshortcuts?

For the same reasons, as under (2) we can not use [] here, unless under a
specific regime, like: 

\startshortcuts
no setup commands, only [short] cuts
\stopshortcuts 

but i see more dangers than benefits. 

Anyhow, to prove the concept: 

\unprotect

\def\defineshortcut%
  {\dotripleargument\dodefineshortcut}

\def\dodefineshortcut[#1][#2][#3]%
  {\ifthirdargument
     \doifelsenothing{#1}
       {\dododefineshortcut[<>][#2][#3]}
       {\dododefineshortcut[#1][#2][#3]}%
   \else\ifsecondargument
     \dododefineshortcut[<>][#1][#2]%
   \else
     \dododefineshortcut[<>][][#1]%
   \fi\fi}

\def\dododefineshortcut[#1#2][#3][#4]% #1 is the trigger, #2 the delimiter
  {\doifundefined{\??te\??te\string#2}{\letvalue{\??te\??te\string#2}=#1}%
   \defineactivecharacter #1 {\@EA\doshortcut\string#2} %
   \getparameters
     [\??te\string#2#3]
     [\c!commandos=,\c!commando=,\c!letter=,\c!kleur=,#4]}

\def\doshortcut#1%
  {\ifmmode
     \getvalue{\??te\??te#1}%
   \else
     \bgroup
     \catcode`#1=\@@other
     \def\dodoshortcut##1#1%
       {\def\shorttag{\??te#1}%
        \def\shortcut{##1}%
        \dododoshortcut##1:\end}%
     \@EA\dodoshortcut
   \fi}

\def\dododoshortcut#1:#2\end
  {\doifelsenothing{#2}
     {\doifundefinedelse{\shorttag\c!commandos}
        {\shortcut}
        {\@EA\dodododoshortcut\@EA\shorttag\@EA:\shortcut:\end}}
     {\doifundefinedelse{\shorttag#1\c!commandos}
        {\shortcut}
        {\dodododoshortcut\shorttag#1:#2\end}}%
   \egroup}

\def\dodododoshortcut#1:#2:\end
  {\getvalue{#1\c!commandos}%
   \doattributes{#1}\c!letter\c!kleur{\getvalue{#1\c!commando}{#2}}}

\defineshortcut [<>] [i] [letter=\it]
\defineshortcut [()] [b] [letter=\bf]
\defineshortcut [++] [s] [letter=\sl]
\defineshortcut [//] [u] [letter=\underbars]
\defineshortcut [--] [a] [letter=\overstrike]

it seems <i:to work> well
it seems (b:to work) well
it seems +s:to work+ well
it seems /u:to work/ well
it seems -a:to work- well

But i must admit that i never used it so far, just playing a bit around -) 

Beware, this kind of trickery can spoil utility file loading in certain
cases [catcode clashing].  

Hans
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