Next word macro inside braces

Question

I have defined a macro that highlights the next word using

\def!##1 {\hkw{##1} }%

where in this scope, ! is an active character. So it works fine to write.

\emph{This is a !good example}

but not

\emph{This example is !good}

where it would complain about ! Argument of ! has an extra }..

Is there a nice way to let ! consider everything up to the next space, but at most everything in the current group, as its argument?

Answer 1

I took Martin’s answer to a related question and simplified it a bit:

With this code

\documentclass{article}


% next word parser, based on https://tex.stackexchange.com/a/11925/15107
\makeatletter
\def\consumenextword#1{%
  \begingroup
  \let\@cmd#1%
  \def\@selectedword{}%
  \consumenextword@
}

\def\consumenextword@{%
  \futurelet\ntoken\consumenextword@@
}

\def\consumenextword@@{%
  \ifcase 0%
    \ifx\ntoken\@sptoken 0\else
    \ifcat a\ntoken 1\else
    \ifcat 0\ntoken 2\fi% test of token is catcode "other"
    \fi\fi
  \relax
    \expandafter\consumenextword@end
  \or
    \expandafter\consumenextword@add
  \else
    \expandafter\consumenextword@checknum
  \fi
}

% Checks if token is a number (ASCII 48-57)
\def\consumenextword@checknum#1{%
  \ifcase 0%
    \ifnum`#1>47
    \ifnum`#1<58 1\fi\fi
  \relax
    \def\next{\consumenextword@end#1}%
  \else
    \def\next{\consumenextword@add{#1}}%
  \fi
  \next
}

\def\consumenextword@add#1{%
  \edef\@selectedword{\@selectedword#1}%
  \consumenextword@
}

\def\consumenextword@end{%
  \@cmd\@selectedword%
  \endgroup%
}
\makeatother

\catcode`!=\active
\def!{\consumenextword{\textbf}}


\begin{document}
This is a !good example, and this !is2. Also works at the end of the !Line

And well well in an \textit{!argument}.
\end{document}

I get this output: