[Tex/LaTex] the right way to redefine macros defined by babel

babelmacrosnamingpatching

If I want to use the babel package and redefine a macro such as \contentsname, what is the right way to go about this? Just putting \renewcommand in the preamble doesn't work.

This sort of works

\documentclass{article}
\usepackage[english]{babel}
\AtBeginDocument{%
        \renewcommand\contentsname{Foo}%
}
\begin{document}
% \selectlanguage{english}
\tableofcontents
\end{document}

but if you uncomment the \selectlanguage{english}, the definition is undone.

The best I could come up with is to use the following.

\usepackage{etoolbox}
\patchcmd\captionsenglish{Contents}{Foo}{}{}

Best Answer

Use \addto\captionsenglish.

\documentclass{article}
\usepackage[english]{babel}
\addto\captionsenglish{%
  \renewcommand\contentsname{Foo}%
}
\begin{document}
\selectlanguage{english}% For testing purposes
\tableofcontents
\end{document}

EDIT: See e.g p. 78 of the babel documentation, where the definitions are changed for the Esperanto language (\addto\captionsesperanto).

Related Solutions

[Tex/LaTex] babel shorthand “| doesn’t work in macros

It works if you switch the shorthand on before defining the command, or if you define the command after \begin{document} when shorthands are active.

As Joseph commented, it's recommendable to switch it off immediately afterwards, so that the active shorthand doesn't affect other commands.

\documentclass{article}
\usepackage[ngerman]{babel}
\shorthandon{"}
\newcommand{\foo}{"|}
\shorthandoff{"}
\begin{document}
ff

f"|f

f\foo f
\end{document}

example output

Alternatively, you could switch it on locally within the macro definition, similar as written here by egreg, and made robust, so it can be used within moving arguments, such as \chapter and \section headings and captions.

\DeclareRobustCommand{\foo}{\shorthandon{"}\scantokens{"|\endinput}}

However, it might be useful to have a part in the preamble where shorthands are active, as in the first solution, so you can use them in your commands such as in text arguments to macros.

[Tex/LaTex] How to redefine or patch the ‘\newcommand’ command

Tackling the problem as posed is tricky due to the way \newcommand works. Heiko's approach is probably more elegant, but one possible method is to use xparse to deal with the syntax of \newcommand, and letltxmacro to deal with the way \newcommand is set up

\documentclass{article}
\usepackage{letltxmacro,xparse}
\makeatletter
\LetLtxMacro{\saved@newcommand}{\newcommand}
\DeclareDocumentCommand{\newcommand}{s+mo+o+m}{%
  \begingroup
  \edef\x{%
    \endgroup
    \ifdefined#2%
      \unexpanded{%
          \renewcommand{#2}%
            {%
              \PackageError{lazyfail}
                {Expanding ambiguous command \protect #2}%
                \@ehc
            }%
        }
    \else
      \noexpand\saved@newcommand
        \IfBooleanT{#1}{*}%
        {\noexpand#2}%
        \IfNoValueF{#3}{[#3]}%
        \IfNoValueF{#4}{[\unexpanded{#4}]}%
        {\unexpanded{#5}}
    \fi
  }%
  \x
}
\makeatother
\begin{document}
\newcommand{\cmd}{FIRST}   %
\cmd                       % outputs FIRST
\newcommand{\cmd}{SECOND}  % no problem yet
\cmd                       % error: expanding ambiguous command
\renewcommand{\cmd}{THIRD} %
\cmd                       % outputs THIRD
\end{document}

The approach here is to grab all of the arguments to the redefined \newcommand in one go, then work out whether they are to be 'recycled' or not.

Of course, you could set all of this up without xparse, but it would be a pain in the next: lots of \@ifstar and \@ifnextchar ( or slightly better \@testopt) stuff and several auxiliaries.

Best Answer

Related Solutions

[Tex/LaTex] babel shorthand “| doesn’t work in macros

[Tex/LaTex] How to redefine or patch the ‘\newcommand’ command

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